Deficiency or Adaptation

How to read this sheet

Nine terms carry the whole document.

Front foot lands

labs call it: foot contact / FC

The frame where the stride foot first touches the mound. Most measurements get taken here because it's the last stable moment before everything explodes.

Peak layback

labs call it: maximum external rotation / MER

The frame where the forearm is turned back the farthest — palm facing roughly toward second base. This is the instant the elbow and shoulder take their biggest hit.

Release

labs call it: ball release / BR

The frame the ball leaves the fingers. The three frames — foot lands, peak layback, release — are the only ones worth freezing.

Elbow load

labs call it: elbow varus torque

The twisting force trying to pry the inside of the elbow open at peak layback. This is the number that tracks with UCL trouble. An average pitcher runs about 100 Nm — roughly the twist of hanging a 75-pound weight off the end of a one-foot bar.

Size-adjusted

labs call it: normalized (%BW×H)

The same load divided by the pitcher's body weight and height, so a 5'10"/170 and a 6'5"/240 can be compared fairly. Reported as a percentage — 6% or higher is the group researchers flag as high-risk.

The sequence

labs call it: kinematic sequence

Hips turn, then chest, then arm, then hand — each one peaking later and faster than the one before. It's a whip, not a shove. When the order breaks, the arm pays.

Stress per mph

labs call it: efficiency

How much velocity he's getting for the load he's paying. This — not raw load — is the number that decides whether a pattern is a problem. High load with high output is expected. High load with low output is the red flag.

Arm level with the shoulders

labs call it: 90° shoulder abduction

Upper arm at a right angle to the torso, elbow at about shoulder height. Nearly every arm-health finding in the research points back to being close to this at both foot landing and release.

Degrees, quickly

for the angle numbers below

90° is a right angle (an "L"). 45° is halfway to that. 180° is a straight line. When you see "45 ± 9°," that means the average is 45° and most pitchers land between 36° and 54°.

Four gates before you change anything

Every source that actually publishes data lands in the same place: most things that look wrong are either downstream of a physical limit, or they are the price of something the pitcher is getting paid for. Run these in order.

Gate 1

Can he physically get there?

Check his range of motion and strength before you cue a position. Driveline's stated order is soft tissue → get the range back → get strong in that new range → then refine mechanics. Drilling a position an athlete has no range for just teaches him to fake it somewhere else.

Classic example: a pitcher with low hip-to-shoulder separation is often tight because his hips are weak and his body is protecting itself — not because he doesn't know how to move.

Gate 2

What is it actually costing?

A pattern is only a problem if it bills you in one of three currencies: velocity, command, or arm stress. If it bills none of the three, it's a signature, not a flaw.

Get the number before the opinion — mph, how far he misses by, and size-adjusted elbow load.

Gate 3

Cause or symptom?

The far end of the chain pays for debts at the near end. A foot that lands open is usually a lead hip that can't rotate. A pushing arm is usually a chest that opened early. Fix the lowest link that's genuinely broken and re-film before you touch anything above it.

Gate 4

Is the trade already good?

In a study of 523 elite pitchers, the high-load group was carrying 28% more elbow load for 1% more velocity. That's the bad trade. The reverse — a "flaw" that costs a tick and buys movement, deception, or health — is a good one. Price it, don't judge it.

The numbers you're comparing against

These are population averages with real spread — use them to locate a pitcher, not to grade him. Where a number is abstract, the plain-English equivalent is in the same cell.

Reference values, in plain English
What it is	When to look	Normal range	Why it matters	Source
How far he stridesstride length	The instant the front foot touches down	About 83% of his height, give or take 4%. A 6'0" pitcher strides roughly 5 feet — call it 57 to 63 inches.	The most reliable lower-body velocity predictor there is. Every extra 1% of his height in stride is worth about 0.7 mph, and stride length alone explained roughly a quarter of why one pitcher throws harder than another.	ASMI · SportRxiv
How bent his front knee is when he landslead knee flexion at contact	The instant the front foot touches down	Bent about 45° — halfway between straight and an "L." Most pitchers land between 36° and 54°.	Here's the surprise: the angle at landing had no measurable effect on velocity. Stop coaching the landing angle. What matters is what the knee does after it lands.	ASMI · SportRxiv
How fast the front knee straightenslead knee extension velocity	From foot landing to release	About 350 degrees per second — it should sweep through a right angle in about a quarter of a second. Under 242°/s reads as a soft front leg.	This is the real measure of the front-leg block. Braking the hips is what makes the chest spin fast. A knee that keeps folding absorbs the energy instead of bouncing it up the chain.	Driveline
Where the throwing arm sits relative to the shouldersshoulder abduction	The instant the front foot touches down	Upper arm roughly level with the shoulders — a right angle to the torso 93 ± 11°. Most land between 82° and 104°.	Drifting away from level in either direction cuts how much layback he can get, raises elbow load, and makes the shoulder joint less stable under load.	ASMI
Where the arm sits at releaseshoulder abduction at release	The instant the ball leaves the hand	Still about level with the shoulders ~90°	More arm elevation at release is linked to less elbow load. This is one of the cleaner levers you can actually pull.	Fleisig
How bent the throwing elbow is when he landselbow flexion at contact	The instant the front foot touches down	Bent to about a right angle 90 ± 15°. Most land between 75° and 105°.	A more folded elbow at landing is linked to more elbow load — the layback event gets compressed into a shorter, sharper arc.	ASMI · Fleisig
How far the elbow sits behind the shoulder lineshoulder horizontal abduction — the "scap load"	The instant the front foot touches down	ASMI says about 20°; Driveline's own data averages closer to 40°, peaking near 57°. Under 5° means he's barely loading the shoulder blade at all.	Pulling the elbow behind the shoulder line stretches the chest and gives the arm runway to accelerate. Without it, the elbow has to supply the speed itself.	ASMI · Driveline
How turned-back the forearm already is when he landsshoulder external rotation at contact	The instant the front foot touches down	Roughly halfway to full layback ~45°	Arriving already turned over is linked to less elbow load. Arriving still packed means the layback happens as a violent snap instead of a long sweep.	ASMI · Fleisig
How much the hips outrun the shouldership–shoulder separation	The instant the front foot touches down	Hips open 40 to 50° more than the shoulders. Driveline calls 48° elite.	Treat this as a means, not a scoreboard. One study found no direct link to velocity at all. Another found that more separation at landing came with more elbow load. Chase it only when the chest genuinely isn't turning fast.	Driveline · Wake Forest
How closed his chest still is when he landstrunk orientation at contact	The instant the front foot touches down	Chest still turned about 10° away from the plate	Staying stacked and closed at landing is linked to less elbow load. Flying open with the chest is one of the more expensive habits on this list.	Driveline · Fleisig
How far he leans away from his throwing armlateral / contralateral trunk tilt	The instant the ball leaves the hand	Over-the-top guys lean about 34°; sidearmers about 24°. Past 48° is a stress flag.	This is how a shorter pitcher manufactures a high release point — and it costs him. More sideways lean at release is linked to more elbow load.	Fleisig · Driveline
How far he bends forward over the front legforward trunk tilt	The instant the ball leaves the hand	No clean target — measure his and track it	Of every position Driveline measured, this one tracked with velocity the most — it accounted for about 20% of the velocity difference between pitchers, and it's where extension toward the plate comes from. It also raises elbow load. Straight velocity-for-stress trade.	Driveline
Elbow loadelbow varus torque	Right around peak layback	About 100 Nm — the twist of hanging a 75-lb weight off a one-foot bar. Published range runs 60 to 120 Nm. Size-adjusted, 6% or higher is the high-risk group.	Lab tests put UCL failure in roughly this same range — which means the forearm muscles are covering the gap on every single pitch. That's why fatigue matters so much.	Driveline · Wake Forest
Pull trying to yank the arm out of the socketshoulder distraction force	Release and the arm slowing down	Over 225 pounds >1000 N	Roughly his own bodyweight pulling the arm bone away from the shoulder socket, every pitch. The back of the rotator cuff is what stops it — which is why deceleration training isn't optional.	Driveline · ASMI
Twist and forward shear on the shouldershoulder internal rotation torque / anterior shear	Just before peak layback	About 50 ft-lb of twist 67 Nm, plus about 70 lb of forward shear 310 N	The front of the shoulder capsule is being pushed forward at the same moment the elbow is being pried open. This is the single most dangerous instant in the delivery.	Fleisig
The order things fire inkinematic sequence	Across the whole delivery	Hips → chest → arm → hand. The hand's internal rotation tops out near 7,000°/s — about 19 full turns per second, the fastest motion the human body produces.	Each segment should peak later and faster than the one before, then slow down to hand its speed forward. When the order breaks, the arm is generating what it should have been given.	ABBS · ASMI

Red stripe — costs arm health Amber stripe — costs velocity or command Slate stripe — commonly mislabeled: check before you touch it

Motor preference: why two clean deliveries look nothing alike

Before you call something a flaw, check whether it's a preference. The ActionTypes framework sorts athletes by how they naturally organize movement — and the profiles predict several of the exact things coaches most often try to standardize.

The four axes, and what each one predicts on the mound
The axis	One type	The other type	What it changes in his delivery
How he loads the groundterrestrial / aerial	Ground-loader — weight sits toward his heels, slow low leg lift, back knee bends right away, can pause at the top without losing anything, drives from the hips, lands heel-first. His lower body starts the movement and the upper body follows.	Springer — weight sits toward the balls of his feet, fast high leg lift with no pause, back leg barely bends, shoulders start the movement. He rebounds off the ground rather than pushing off it.	Leg-lift height and tempo, how deep he sits into the back leg, whether "get more load in the back leg" helps him or wrecks him, and whether a controlled fall forward is a fault or the whole engine.
How much he twistsassociated / dissociated	One-piece turner — smaller chest rotation, closes his hips more to make up for having less twist available.	Spiral turner — bigger gap between hips and shoulders, less hip closing needed.	Directly predicts his natural separation number. A one-piece turner chasing a spiral turner's separation is chasing range he isn't built to organize.
Which side of his body he lives onanterior / posterior chain	Front-side — quads, hip flexors, chest. He pushes.	Back-side — glutes, hamstrings, lats. He pulls.	Which cues land ("claw the rubber back toward second" is a back-side cue), and which lifts he actually expresses power in.
Which way his hand naturally turnspronator / supinator	Palm-down bias at release.	Palm-up bias at release.	Arm slot and release point get treated as expressions of preference rather than choices — and it predicts which second pitch will come easy (changeup and sinker vs. slider and sweeper).

Use this honestly. Motor preference is a coaching framework, not settled science — nothing like the evidence behind elbow load or stride length. Use it as a reason to ask a question: when a pitcher fights a change that should obviously help him, preference is a plausible explanation for why. Don't use it as a diagnosis, and don't let it override a measured arm-health flag. The framework's own core claim is the useful part: coaching a guy against how he's built is where avoidable oblique strains and arm injuries come from.

The chain, ground up

Each link opens with the anatomy — which muscles are working, whether they're shortening, lengthening, or holding, what to test, and what to load. Then the diagnostic rows: what you see on film, why it happens, what changes it, and the case for leaving it alone.

Shortening = the muscle is producing the movement. Lengthening = it's braking a movement while being stretched (this is where most injuries happen). Holding = it's not moving, just keeping a position stable.

Link 01 · Drive side

Back foot & ankle

The only thing touching the ground while his body is speeding up. Everything the delivery gets, it gets here first — and force is only half of it. How long he can keep applying that force is the other half.

Muscles & what they're doing

Calf (soleus and gastrocnemius) — lengthening as the shin travels forward over the foot, then shortening to push. The deep calf does most of it because the knee is bent.

Deep arch muscle (tibialis posterior) — holding. This is the anti-collapse muscle.

Outside of the shin (peroneals) — holding, keeps the big-toe side of the foot pressed down.

Front of the shin (tibialis anterior) — lengthening, controls how fast the shin travels. Small foot muscles hold the arch up under load.

Test it

Knee-to-wall ankle test, both sides — you want 4 to 5 inches
Single-leg heel raises to failure (calf endurance)
Does the arch flatten when he stands on one leg?
Big-toe extension range — he needs it to finish the push

Load it

Heavy calf raises, straight-leg and bent-knee, 3–4 seconds lowering
Seated calf raise, heavy, 8–12 reps
Tibialis raises for the front of the shin
Short-foot and toe-splay work for the small foot muscles
Heavy sled marches and lateral sled drags — long ground contact, force going sideways and forward
Ankle mobility work before the loading, not instead of it

See

Heel pops off the rubber early; the foot rolls in and the arch collapses; he's off the rubber well before the front foot lands.

Why

He can only push the ground while the foot is still loaded. Coming off early cuts the time he has to apply force, so even the same push produces less speed. Think of it as a shorter runway, not a weaker engine.

Usually a stiff ankle or a calf that can't hold a stretched position under load.

Fix

Get the ankle range back, then load it: heavy slow-lowering calf work and split-squat holds. Banded lateral drives and skater bounds to teach sideways force.

Cue him sideways, not upward — Tread's version is "claw or pull the rubber back toward second," which gets the glutes and hamstrings involved instead of the quads.

Or leave it

Coming off the rubber early raises his tempo, and tempo steals timing from hitters. It's also just how a springer-type athlete is built. If the velocity and command are there, a longer drive phase buys you nothing you can measure.

See

No toe drag at all, or a drag line that hooks toward his arm side instead of running toward the plate.

Why

The drag line is a readout of when his hips turned, not a cause of anything. A hooked drag means the hips opened before the front foot landed and dragged the foot around with them.

Fix

Don't drill the drag. Go upstream to back-hip rotation and hip timing (links 03–04). The drag line fixes itself when the hips wait.

Or leave it

Guys with a lot of back-hip range naturally hook the drag while still holding their separation. If the separation number at landing is fine, the line on the mound is cosmetic.

Link 02 · Drive side

Back knee

The knee decides which direction his push points. A knee that straightens early sends him up. A knee that stays bent while the hip drives sends him out toward the plate.

Muscles & what they're doing

Quads (front of the thigh) — lengthening into the load, shortening out of it. Over-relying on these is the fault, not the muscle itself.

Hamstrings (back of the thigh) — working alongside the glutes to extend the hip while the knee stays bent. This pairing is what points him at the plate instead of at the sky.

Big inner thigh muscle (adductor magnus) — a major and under-credited hip extender in the drive. Main butt muscle (gluteus maximus) is the primary engine.

Test it

Rear-foot-elevated split squat — depth and control
Single-leg broad jump: distance versus height tells you which way he pushes
Lateral bound distance, back leg versus front leg
Can he hinge at the hip and load the hamstring without using his low back?

Load it

Trap-bar deadlift and Romanian deadlift — build the hinge before the push
Rear-foot-elevated split squat, heavy
Skater bounds and lateral bounds for sideways springiness
Lateral sled drag and band-resisted lateral drives
Step-back roll-ins, rocker drill, step-back windups — set up the drill so the pattern happens on its own instead of cueing it

See

He rises up at the top of leg lift; there's a visible float or jump; the back knee straightens before his hips have moved toward the plate.

Why

Quad-driven knee extension sends him up. Force that goes up doesn't become ball speed — it becomes hang time. Tread names this as the most common lower-half fault: it turns a rotational athlete into a linear pusher.

Fix

Reverse the pattern with drill setups rather than cues: step-back roll-ins, step-back windups, a properly run rocker drill. In the weight room: hinge strength, lateral sled drives, skater bounds.

Tread's own check — if he can hit the low 80s in warmups feeling like his lower half is throwing the ball, the timing is right.

Or leave it

A controlled rise-then-drop raises his release point and steepens the angle the ball comes in on. If his identity is a downhill sinker or a curveball he lives on, that rise is buying him pitch shape. Judge it on ball flight, not on the silhouette.

See

Back knee caves inward at peak load; the hip drops on that side; the stride ends up short or closed because of it.

Why

The side-hip muscles aren't holding. Once the pelvis tips, the chest has to counter-lean and the arm inherits the correction. In high school pitchers, better balance and pelvic control standing on the back leg came with less load on the shoulder r = .30.

Fix

Banded hip abduction, Copenhagen planks, lateral lunge with a reach, single-leg balance work when he's tired. Then re-test: the average pitcher's pelvis wobbles about 6° during a single-leg lift test.

Or leave it

Rarely. This is the version of a lower-half fault that shows up on the shoulder's bill, not just the radar gun.

Link 03 · Drive side

Back hip

To rotate around a loaded leg he needs the hip to turn inward on that side. To hold his counter-rotation while he strides he needs it to turn outward and hold. Missing either one and the hips open early, because they have nowhere else to go.

Muscles & what they're doing

Main butt muscle (gluteus maximus) — the primary engine for extending and rotating the hip; shortening through the drive.

Side of the hip (gluteus medius and minimus) — holding, keeps the pelvis level. Measured at 20 to 40%+ of a max effort through acceleration and deceleration, and it tracks with how well the shoulder blade is controlled.

Deep hip rotators (piriformis and friends) — holding the ball of the hip centered in the socket while the pelvis turns on it.

Inner thigh (adductors) — lengthening as the stride opens, then shortening to help extend the hip.

Test it

Hip rotation both directions, both sides — flag a 5°+ difference in inward rotation
Total rotation per hip (inward + outward), not just inward
Hip airplane — can he control rotation over a loaded leg?
Copenhagen plank hold time for the inner thigh

Load it

90/90 hip switches, then loaded; hip rotation stretches held under tension
Banded hip airplane; banded hip abduction (Driveline's named side-hip prescription)
Wall press dead bug and bear crawl — hip rotation plus front-side core
Copenhagen plank; adductor slides
Single-leg Romanian deadlift; hip thrust; cable hip rotations
Step-back med-ball shotput to reload the back hip

See

He loses the hinge and sits back in the bucket; his belt buckle points at the plate before the front foot lands; the separation number comes in low.

Why

Without back-hip range, the pelvis can't turn around the leg — so it turns the whole leg instead. That spends the separation window before the chest has anything to separate from. Less stretch across the side abs and the lat, less snap back.

Fix

Get the rotation back, then load it. Driveline's published case paired hip-rotation work (wall press dead bug, bear crawl, banded hip abduction) with step-back med-ball shotput and lateral lunge with reach.

Or leave it

Early hips are only a problem if the chest goes with them. Some pitchers open the hips early and generate all their separation through the mid-back instead. Measure the separation, not the hip timing by itself.

See

His back hip turns inward about 5° less than his front hip does.

Why

A 5° difference in inward hip rotation predicted back and abdominal injuries across 258 professional player-seasons — not shoulder or elbow, but core. Tight hips also raise the load on the shoulder, because the rotation has to come from somewhere.

Fix

Restore it, then load it. Mobility alone slides back within a week. Range he can't control is range he won't use. Track total rotation per hip.

Or leave it

No. This is one of the few screen findings with a direct published injury link.

Link 04 · Base of the chain

Hips & pelvis

First segment to peak in the sequence. Its job is to peak early and get out of the way so the chest can be accelerated against it.

Muscles & what they're doing

Back-side butt muscle — shortening to extend and rotate; this is what drives hip turning speed.

Side abs, working diagonally (internal oblique on the throwing side, external oblique on the glove side) — shortening to turn the hips underneath a chest that's staying put.

Deep corset muscle and diaphragm (transverse abdominis) — holding, creating pressure in the trunk. Without it the diagonal sling has nothing to pull against.

Deep low back and spine stabilizers (quadratus lumborum, multifidus) — holding, side to side and in rotation.

Test it

When his hips peak, as a share of the delivery — earlier is better
Seated trunk rotation test (isolates hips from chest)
Pallof press hold quality — can he resist rotation before he produces it?
Rotational med-ball throw speed, both directions

Load it

Pallof press and half-kneeling anti-rotation holds
Landmine rotations; cable chops and lifts
Rotational and shotput med-ball throws — 3 to 6 reps, full rest
Hip thrusts and glute bridges for the back-side extender
Step-back and rocker patterns to move hip initiation earlier

See

His hips peak late in the delivery; hips and chest turn together as one block.

Why

The later his hips peak, the more elbow load he carries. A late hip turn means nothing gets handed off — the arm has to supply its own speed, and the elbow absorbs the difference.

Fix

Start the rotation from the ground earlier: step-back and rocker patterns, med-ball throws timed off the front foot. Back-hip range (link 03) is usually the prerequisite.

Or leave it

Rarely — this is one of the cleaner arm-health levers in the research.

See

Low hip-to-shoulder separation on the report, and someone has already declared it the reason he throws 84.

Why

Two findings complicate the usual story. One study found no link at all between separation and fastball velocity at any point in the delivery. A Wake Forest study of 298 pitchers found that more separation at landing came with more elbow load.

Separation is a way of loading the chest, not a scoreboard. And a one-piece turner is simply built to run less of it.

Fix

Chase it only when his chest genuinely isn't turning fast. Then treat the input — back hip rotation, mid-back rotation, front-side core — not the number itself.

Or leave it

Very often, yes. If he throws hard with modest separation, he's finding his rotation speed somewhere else. Adding separation to a pitcher who doesn't need it can raise his arm bill for nothing.

Link 05 · Lead side

Front hip

After the foot lands, the front hip stops being a leg and becomes an axle. All that speed he built moving forward has to become spin around that point — which only works if the point stays put.

Muscles & what they're doing

Front-side butt muscle — lengthening on landing, then holding to be the axle. This is a braking muscle here, not a pushing one.

Side of the front hip — holding; this is the reason the hip doesn't drift forward.

Inner thigh — lengthening to decelerate the stride, then stabilizing.

Hamstrings — lengthening to control the hip as his chest tips forward over the leg.

Deep rotators — supply the inward turn his body rotates over.

Test it

Front-hip inward rotation, seated and lying face-down
Single-leg Romanian deadlift — control and depth
Drop-and-stick landing quality
Split-squat hold time at depth

Load it

Split-squat holds at depth, 20 to 45 seconds
Single-leg Romanian deadlift; Romanian deadlift with a 2-second pause at the bottom
Lateral lunge with reach; Copenhagen plank
Hurdle hops with a stuck landing; box drop and hold
Band-resisted inward hip rotation; pigeon-to-half-kneeling for range
Half-kneeling med-ball scoop toss — rotation over a stable front leg

See

The front hip keeps sliding toward the plate after the foot lands, instead of parking and letting the body rotate around it.

Why

Driveline defines a good block as the hip staying basically in place from landing to release while the body turns around it. If the hip drifts, his speed stays linear and never becomes chest rotation.

Fix

Front-leg braking strength first — split-squat holds, single-leg Romanian deadlifts, hurdle-hop stick landings, box drop and hold. Then re-measure how fast the knee straightens.

Or leave it

Sliding forward buys extension — releasing the ball closer to the plate makes the pitch play faster than the gun says and flattens the angle. Some pitchers ride out six-plus inches of extension on purpose. The bill shows up in elbow load; check it before you decide.

See

Limited inward rotation in the front hip on the screen; the front side stalls; his chest turns but the front leg doesn't roll over with it.

Why

To rotate over a hip, that hip has to turn inward. When it can't, the low back tries to supply the rotation instead — and the low back only has about 13° of rotation in total. That's exactly why this shows up as oblique and low-back strains. It also forces the chest to turn early, which rushes the arm.

Fix

Get the front-hip inward rotation back (90/90 work, pigeon-to-half-kneeling), then get strong in it — Romanian deadlift with a 2-second pause, half-kneeling med-ball scoop toss.

Or leave it

No. This is the single most common upstream cause of a fault that ends up getting coached at the foot or the arm.

Link 06 · Lead side

Front knee

The block is a collision. Stopping the hips is what makes the chest spin fast — same reason a car stops and the passenger keeps going. A soft knee absorbs the collision instead of bouncing it back up the chain.

Muscles & what they're doing

Quads — all three jobs in one landing: lengthening on impact, holding at the transition, then shortening to snap the knee straight. How fast that last part happens is the output you measure.

Hamstrings — working alongside to protect the knee and control the hip while the quad straightens it. Their ability to brake while lengthening is what makes a violent block survivable.

Calf — helps control the knee at the far end of extension.

Test it

How fast the front knee straightens from landing to release — target ~350°/s, flag under 242°/s
Drop-jump: how fast he leaves the ground after landing
Nordic hamstring curl — where does he break?
Box drop and stick — does he hold, or does he sink?

Load it

Box drops with a stuck landing; drop jumps; landings from height
Nordic hamstring curls and reverse Nordics (lengthening-focused)
Heavy split-squat holds at his actual landing angle
Band-resisted knee lockouts
Run it in blocks: braking work first, then holding work, then explosive work

See

The knee keeps bending through release; he sinks and then pushes. Knee straightening speed under about 242°/s.

Why

Driveline's target is around 350°/s, and they want continuous straightening after the foot lands — not sink-then-push. Fair warning: a fast-straightening knee is also linked to more elbow load. A good block genuinely does raise the arm bill, and buys velocity for it.

Fix

Landing and braking capacity first: box drops with a stick, landings from height, band-resisted lockouts. Then drills that punish a soft front side.

Or leave it

A softer block is a legitimate low-stress strategy for a pitcher whose value is command and movement rather than velocity. It's also the right call for someone whose low back or knee won't tolerate a violent stop.

See

He lands with what looks like too much (or too little) knee bend, and someone wants to standardize it.

Why

The knee angle at the moment he lands showed no effect on velocity. The normal range is wide — anywhere from 36° to 54° of bend is ordinary. What predicts velocity is what happens between landing and release, not the frame you froze.

Fix

Stop coaching the landing angle. Measure how fast the knee straightens instead.

Or leave it

Yes — one of the most-coached, least-supported cues in the delivery.

See

The knee snaps into full lockout, violently, right at release.

Why

That's what a maximal block looks like. Very fast knee straightening, very fast chest rotation, and real load through the hamstring, the knee tendon, and the low back.

Fix

Nothing mechanical. Build the tissue that has to survive it — Nordics, heavy lengthening hamstring work, back-side strength — and keep an eye on the low back.

Or leave it

Leave it. The best blockers in the game do exactly this. Softening it to make the delivery look calmer is a direct subtraction from his velocity.

Link 07 · Lead side

Front foot & landing

Where and how the front foot lands sets his stride length, how much his hips are allowed to turn, and where the ball comes out — all at once. It's also the position most often blamed for something that isn't its fault.

Muscles & what they're doing

Front of the shin — lengthening, controlling the foot from heel contact down to the forefoot.

Calf — lengthening to absorb the hit, then holding so the leg becomes a rigid post for the block.

Outside shin and deep arch muscle — holding. These decide whether the foot becomes a stable base or a collapsing one.

Side-hip muscles — holding. Landing control actually starts above the foot, not at it.

Test it

Stride length as a share of his height (normal is about 83%)
Where the foot lands relative to a line to the plate
Ankle range — usually the thing capping stride length
Inner-thigh length and braking strength
Single-leg landing control off a box

Load it

Landing progressions — two feet, then one foot, then sideways
Heavy calf and shin work for absorption capacity
Adductor slides and Copenhagens so a longer stride is tolerable
Broad jumps and lateral bounds for forward power
Tape or a marker on the mound as the constraint — let him find it instead of telling him

See

Stride noticeably short — under about 78% of his height.

Why

Stride length is the best-supported lower-body velocity predictor there is: every extra 1% of his height is worth about 0.7 mph, and it explained roughly a quarter of the velocity difference between pitchers. Normal is about 83% of height. A short stride also raises his release point and shortens his extension toward the plate.

Fix

Find the actual limiter before you add distance — back-leg power, ankle range, inner-thigh length, or fear of landing. Then use a tape marker so he organizes into it himself.

Or leave it

A short stride raises the release point and steepens the angle the ball comes in on — genuinely useful if he lives on a downhill sinker or a big curveball, and it shortens the time his arm spends under load. But if he lives at the top of the zone with a four-seam, the short stride is costing him.

See

Lands closed — foot planted well across the line to the plate. Crossfire.

Why

A closed landing restricts how much his hips can turn, so the chest has to rotate over a partly locked pelvis. That raises the demand on the low back and side abs, and it can shorten his effective stride.

Fix

Only if it's costing him. Address back-hip range and stride direction with a lane constraint on the mound.

Or leave it

Crossfire is deception. It changes where the hitter expects the ball to appear, and it's a real weapon for a lefty against lefties or for anyone throwing from a lower slot. If separation, health, and command all hold, this is an identity, not a fault.

See

Front foot flies open at landing; the toe points toward the on-deck circle.

Why

Usually not a foot problem at all. He's pre-turning the foot to buy rotation his front hip can't give him. It lets the hips leak open early and drains the separation window.

Fix

Restore front-hip inward rotation first (link 05), then re-film. If the foot still opens once the hip has range, then constrain the landing.

Or leave it

An open landing with intact separation and a firm block is just a rotational preference. Check the separation number before you touch it.

See

Heel-first, stiff, audible landing with no roll onto the forefoot.

Why

No absorption at the ankle sends the impact spike straight up the chain into the low back, and forces the knee to do the entire job of the block by itself.

Fix

Ankle range plus calf braking strength; teach heel-to-forefoot landing with landing progressions.

Or leave it

Heel-first landing is normal for a ground-loader type, and some hard-throwing blockers land nearly flat on purpose. If the ankle range is normal and the low back is quiet, it's a strategy.

Link 08 · Trunk

Low back & front-side core

The low back has roughly 13° of rotation available, total. It's a transmitter, not a generator. Every degree of rotation the hips and mid-back fail to supply gets demanded here — and it can't pay.

Muscles & what they're doing

Side abs, working diagonally (obliques) — stretched at peak separation, then shortening hard through the turn. They hit peak activity right when his chest is turning fastest, alongside the glutes.

Front abs (rectus abdominis) — shortening to tip him forward over the front leg at release.

Deep corset muscle and diaphragm — holding, creating pressure. This is the platform the diagonal sling pulls against.

Long back muscles and deep spine stabilizers — lengthening and holding. They pay for whatever the hips and mid-back don't supply. This is where oblique and low-back strains come from.

Test it

Do his ribs flare and his pelvis tip forward, at rest and in the delivery?
Single-leg lift test on the back leg — average pelvis wobble is about 6°
Side-plank hold time, both sides
Can he exhale all the way out and keep his ribs down under load?

Load it

Wall press dead bug with a full exhale; 90/90 breathing
Bear crawl and bear-position holds
Ab wheel rollouts, side planks, Pallof presses
Suitcase carries and offset-load carries
Half-kneeling med-ball scoop toss; landmine rotation
Order matters: pressure and anti-rotation work before rotational power work

See

Ribs flared up, pelvis tipped forward, big visible arch in the low back through the delivery — the "arch and layback" look.

Why

Flared ribs disconnect the rib cage from the pelvis, so the side abs never actually get stretched — the separation you see on film doesn't turn into stored energy. It also stacks an arched low back on top of a rotating low back, which is the exact combination that produces oblique and back injuries.

Fix

Front-side core work with a full exhale to get the rib cage back over the pelvis, then anti-arch loading, then rotational loading. Don't start with rotational med-ball work.

Or leave it

Some of the biggest layback in the sport is just spine and rib flexibility in a guy who tolerates it. If it's painless, the separation is real, and the arm bill is normal, it's a signature.

See

His pelvis wobbles front-to-back during a single-leg lift test on the back leg.

Why

In 54 high school pitchers, better pelvic control on the back leg came with less load on the shoulder. Average wobble was about 6°. The link was weaker than in college and pro athletes, so treat it as a direction, not a diagnosis.

Fix

Balance and pelvic-control work standing on the back leg — that's the specific recommendation the authors made.

Or leave it

Worth knowing: it showed no relationship with elbow load or with how hard he pushes the ground. Don't sell it as an elbow intervention.

Link 09 · Trunk

Mid-back & rib cage

The mid-back supplies most of the rotation his chest actually has. Driveline's framing: mid-back rotation is what lets the hips open while the chest stays back. Stiff here, and his separation has to be manufactured at the shoulder or the low back instead.

Muscles & what they're doing

Small spine rotators (rotatores, multifidus) — segment-by-segment rotation. Small muscles, big consequences.

Big back muscle under the armpit (latissimus dorsi) — it runs from the low back all the way to the upper arm bone, so it is the literal mechanical link between trunk and arm. Stretched at peak layback, shortening through acceleration.

Ribs-under-the-armpit muscle (serratus anterior) — anchors the shoulder blade to the rib cage. Working at over 40% of a max effort through acceleration and deceleration.

Rib muscles and diaphragm — rib mobility is mid-back mobility. A locked rib cage can't rotate no matter what the spine can do.

Test it

Seated mid-back rotation, both directions
Rotation on all fours or side-lying with the pelvis locked down
How far he leans away from his arm at release (flag past 48°)
How far he tips forward over his front leg at release
Rib position on a full exhale — mobility screens lie when the ribs are flared

Load it

Side-lying windmill with a full exhale (Driveline's named drill)
Open books; thread-the-needle; all-fours rotation
Landmine rotation; cable chops and lifts
Rotational med-ball throws to load the new range at speed
Lat and chest soft-tissue work first if the restriction is tissue, not joint

See

Chest and hips turn as one unit; measured mid-back rotation is limited.

Why

Without mid-back rotation, the chest starts turning the instant the hips do. The arm gets dragged instead of whipped, and the elbow absorbs the acceleration the chest failed to deliver.

Fix

Mobilize, then load the new range with rotational med-ball work so it sticks under speed. Mobility without loading is gone inside a week.

Or leave it

Stiff-chested throwers who generate velocity through a violent block and fast arm speed absolutely exist — and a one-piece turner is built that way. If the mph is there and the arm bill is normal, you're solving a picture, not a problem.

See

Heavy sideways lean away from the throwing arm at release — the "spine tilt" high slot. Flag past about 48°.

Why

More sideways lean at release comes with more elbow load. Typical is about 34° for over-the-top guys and 24° for sidearmers. The lean is how a shorter pitcher manufactures a high release point.

Fix

Reduce it only if the arm bill is high and he isn't getting paid for the release height. Usually the real fix is a better block, so he doesn't have to lean to clear his front side.

Or leave it

This is how a 6'0" pitcher gets a 6'4" release point and the ride that comes with it. If his four-seam plays at the top of the zone because of that lean, taking it away removes the pitch.

See

He finishes upright — very little forward bend over the front leg.

Why

Of every position Driveline measured, forward tilt at release tracked with velocity the most — roughly 20% of the velocity difference between pitchers — and it's where extension toward the plate comes from. It also raises elbow load, so it's an explicit velocity-for-stress trade.

And you can't tip forward over a leg that's collapsing, so this is frequently a front-knee problem in a chest costume.

Fix

Fix the block first (link 06), then hinge and hamstring strength so he can get over the front side without losing his head line to the target.

Or leave it

Finishing upright protects the arm and often the command. For a pitcher whose margin comes from location rather than velocity, staying tall is a defensible choice.

Link 10 · Arm

Shoulder blade

The platform the arm bone moves on. Where the shoulder blade sits decides how much real layback is available and how long the arm's runway is.

Muscles & what they're doing

Ribs-under-the-armpit muscle (serratus anterior) — pulls the blade forward and rotates it upward; keeps it flat on the rib cage. Working at over 40% of a max effort through acceleration and deceleration. The single most important shoulder-blade muscle for a thrower.

Mid-back between the blades (lower and middle trapezius) — rotate the blade up and pull it back; holding through cocking, then braking through the finish.

Between the blades, deeper (rhomboids) — pull the blade back; braking hard during deceleration.

Small chest muscle under the pec (pectoralis minor) — pulls the blade forward and tips it down. Chronically short in throwers, and usually the thing blocking real retraction.

Neck-to-blade muscles (upper trap, levator) — often over-recruited as a substitute for the two muscles above.

Test it

How far the elbow sits behind the shoulder line at landing (flag under 5–10°)
Does the blade rotate upward smoothly as he raises his arm? Any winging on a wall slide?
Small chest muscle length — lying face-up, does the shoulder sit off the table?
Prone Y and T strength endurance
Side-hip strength — it tracks with shoulder blade control

Load it

Wall slides and bear-position reaches; serratus punches
Prone Y / T / W raises; low-trap raises; face pulls
Landmine press (upward rotation under load)
Release the small chest muscle before you try to strengthen anything
Pivot pickoff (Driveline's primary drill) and scap-retraction throws, cueing the elbow back, not up
Thrower's Ten as the year-round base — the evidence supports blade stability, range of motion, cuff strength and endurance gains

See

Barely any shoulder blade load — the elbow sits at or under 5° behind the shoulder line at landing, or visibly in front of it.

Why

Pulling the blade back stretches the chest and gives the arm room to travel. Driveline's own pitchers average about 40° at landing with a peak near 57°; ASMI puts it around 20°. Below the floor, the arm has no runway and the elbow supplies the speed instead.

Fix

Driveline's stated prescription: pivot pickoff first, scap-retraction throws second, with the cue pointing the elbow backward. Back it up with mid-back and serratus work.

Or leave it

Short, compact arm actions with minimal blade load are a real deception strategy — less time for the hitter to see the ball. If he throws hard with a compact action, adding load may just add elbow stress.

See

The shoulder blade wings off the rib cage, or doesn't rotate upward as the arm goes up.

Why

If the blade doesn't rotate up, the shoulder joint itself has to make up the difference — which pinches the space under the shoulder and cuts how much real layback he can get. Research shows a poorly positioned blade at cocking directly raises the load on the elbow.

Fix

Serratus work (wall slides, bear-position reaches) and mid-back trap work; mid-back mobility upstream, since a rounded upper back physically prevents the blade from rotating up. Add side-hip work too — the link between hip control and blade control is published.

Or leave it

No — this one shows up on both the shoulder's bill and the elbow's.

See

The "inverted W" — both elbows above the shoulder line at landing.

Why

The shape itself has never been shown to be an independent injury risk. What is in the data: the arm being roughly level with the shoulders at landing, and the timing of peak layback relative to when the chest turns. Randy Johnson carried an enormous blade load with his elbows below the shoulder line — the load and the shape are separate things.

Fix

Don't chase the silhouette. Chase arm level with the shoulders and arm timing. Driveline's example of a real problem was an arm at 103° at landing climbing to 135° — that's the elbow climbing, which is a different finding than an inverted W.

Or leave it

Frequently. If his arm is roughly level at landing and on time when the chest turns, the shape of the arm path is his.

See

Both shoulder blades stay locked together — the glove side freezes in place instead of separating from the throwing side.

Why

Driveline's position: blocking with the glove and a firm front side kills shoulder rotation speed — the biggest single contributor to a 90+ fastball — and pulls the neck off the target line. Elite arms show the two shoulder blades clearly disconnecting from each other.

Fix

Coach the glove arm to keep moving and decelerate, not to hold a position. See link 15.

Or leave it

Never worth adding on purpose — but know that "firm front side" is still taught widely enough that you may be undoing someone else's cue.

Link 11 · Arm

Shoulder joint

The arm rotates here at nearly 19 full turns per second — the fastest motion the human body produces. Then over 225 pounds of pull tries to yank the arm bone out of the socket while it slows down. Every pitch.

Muscles & what they're doing

Cocking → Back of the rotator cuff (infraspinatus, teres minor) peaks, shortening to turn the arm back. At the same instant the front of the rotator cuff (subscapularis) is lengthening to brake that turn and protect the front of the joint. The chest, lat, and front shoulder stretch under load — this is the rubber band that pays for acceleration.

Acceleration → Front of the cuff, chest, lat, and the muscle beside the lat (teres major) all shorten to whip the arm forward. Serratus and triceps heavily involved. Pros show noticeably more activation here than amateurs.

Deceleration → Teres minor hits its peak while lengthening, fighting the arm bone being pulled forward and inward — higher than the muscle next to it, which is exactly why post-outing soreness shows up at that spot and not the other. Back shoulder, rhomboids, traps all braking.

Test it

Is the arm level with the shoulders at landing and at release?
Rotation both ways, and total rotation, comparing throwing side to the other side
Peak layback — is it real, or is he faking it by bending the elbow forward?
Prone horizontal abduction and external rotation strength
Sort out whether tightness is capsule, soft tissue, or just how the bone is shaped — before you treat it

Load it

External and internal rotation at 90°, band and cable
Slow-lowering external rotation for the back of the cuff
Prone horizontal abduction; prone external rotation at 90°
Rhythmic stabilization and bottoms-up kettlebell carries for reflexive stability
Reverse-throw plyo work for braking capacity
Soft tissue first when he's tissue-limited: chest, small chest muscle, upper trap, lat, long head of the triceps (Tread's list)
Thrower's Ten as the year-round base

See

The elbow climbs — arm well above level at landing and rising further into cocking. Driveline's real example: 103° at landing climbing to 135°.

Why

Drifting away from level cuts how much layback he can get, raises elbow load, and makes the joint less stable. Here's the nuance that matters: arm elevation at landing is linked to more load, while arm elevation at release is linked to less. The goal isn't "high" or "low" — it's level at both frames.

Fix

Pivot pickoff and scap-retraction throws, cued "elbow back," not "elbow down." Driveline pairs these specifically for the climbing-arm-plus-low-blade-load profile.

Or leave it

Only if his elbow load and his stress-per-mph are both fine. Arm elevation is one of the more reliably fixable things on the report.

See

Not much layback — or "fake layback," where it looks like 180° from the side but turns out to be a forced elbow bend rather than the arm actually turning back.

Why

More real layback is linked to less elbow load, not more. Longer arc to reverse the arm means a lower peak force for the same job. Fake layback gets the look without the arc — so he pays the load and doesn't collect the velocity.

Tread's root causes: balls heavier than 1 lb, standing too close on plyo wall work, over-cueing strikes, an upper half that flies open, guarding after an injury, and tightness in the chest, small chest muscle, upper trap, lat, and long head of the triceps.

Fix

Release the tissue first — that's Tread's explicit order — then throw. Long toss to re-teach a rotational finish. Cap the ball weights: be selective above 1 lb for high school and college, and avoid 2 lb entirely for youth.

Do not drill the position. Layback is an outcome, not an action.

Or leave it

Genuinely limited layback in a guy who tolerates it is a viable, lower-stress build. It's also very often a protective response after an injury — the nervous system limiting range around tissue it doesn't trust yet. Forcing range on that athlete is how you get the next injury.

See

His throwing shoulder turns inward noticeably less than his other shoulder.

Why

The whole body reorganizes around it — this pattern has been linked to changes in how the chest compensates and even to changes in knee mechanics during the pitch. The shoulder isn't the only thing that adjusts.

Fix

Figure out why before you stretch anything — capsule, soft tissue, or the shape of the arm bone itself. Track total rotation side-to-side, not just inward rotation. Then add cuff strength through whatever range you got back.

Or leave it

Some loss on the throwing side is normal adaptation, including bone shape you cannot and should not try to stretch out. Only the soft-tissue portion is a target.

See

The arm arrives at landing still packed and facing down — not turned back at all yet.

Why

Arriving already partly turned over is linked to less elbow load. Arriving packed means the layback happens as a violent snap instead of a long sweep.

Fix

This is arm timing, not shoulder flexibility. Move the arm path earlier relative to the lower half — it usually resolves once the hips stop being late.

Or leave it

A genuinely late arm can be deceptive — the hitter picks the ball up later. Weigh it against the elbow load number, which is where it shows up.

Link 12 · Arm

Elbow

At peak layback the elbow takes a twisting force reported between 60 and 120 Nm — roughly the twist of hanging 45 to 90 pounds off the end of a one-foot bar. Lab tests put UCL failure in that same range, which means the forearm muscles are covering the gap on every single pitch. Fatigue isn't an abstraction.

Muscles & what they're doing

The meat on the inside of the forearm (flexor-pronator mass) — holding and braking against the elbow being pried open at peak layback. This is the tissue standing between the load and the ligament.

Back of the upper arm (triceps) — shortening to straighten the elbow through acceleration. Over-relying on this is the "pushing" pattern.

Front of the upper arm (biceps, brachialis) — lengthening to brake the elbow after release. A common late-outing soreness spot.

Test it

Elbow bend at landing (normal is about a right angle, 75–105°)
Size-adjusted elbow load — 6% or higher is the high-risk group — and stress per mph
Grip strength fresh versus late in an outing
Forearm palm-down strength and endurance

Load it

Dumbbell wrist curls and palm-down rotations; hammer rotations
Heavy grip work — towel hangs, plate pinches, thick-grip carries
Slow-lowering biceps work for braking capacity
Rice bucket or high-rep endurance work late in the week
Thrower's Ten forearm block
Understand what this is: armor. It raises how long he can hold up. It does not lower the load itself.

See

Elbow noticeably more bent than a right angle when the front foot lands.

Why

A more folded elbow at landing is linked to more elbow load — the layback event compresses into a shorter, sharper arc.

A markerless-camera study found four things together — how much layback he gets, elbow bend at peak load, elbow bend at release, and when peak elbow bend happens — predicted about 60% of the elbow load.

Fix

Shoulder blade retraction so the elbow travels back instead of folding; arm timing work. Forearm strength as armor, not as a mechanics fix.

Or leave it

Short-arm actions run a more folded elbow by design and are a legitimate deception and repeatability strategy — especially out of the bullpen. Price the load and decide.

See

The elbow snaps straight very fast; a triceps-driven push finish; the ball cuts and finishes flat.

Why

Faster elbow straightening is linked to more elbow load. Pushing means the chest failed to deliver rotation, so the arm is extending its way to the plate instead of being carried there.

Fix

Work Tread's seven causes in order: cap the ball weights; back him off the plyo wall and rotate the back shoulder through the target line (tape a target so it forces rotation); stop over-cueing strikes; keep the upper half closed at landing; respect post-injury guarding; release the chest, lat and triceps; and stop chasing fake layback.

Long toss is the fastest re-teach — pushing visibly loses distance, so the feedback is instant.

Or leave it

If the cut is the pitch — an actual cutter he lives on — you're looking at his weapon, not his flaw. Confirm on ball-flight data before you take it away.

See

High size-adjusted elbow load, or poor stress per mph. The high-risk cut used in the research is 6% or higher.

Why

The Wake Forest study of 298 pitchers found the high-risk group was spinning the chest fast without the positions to spend it through — less forward tilt at release and a lower arm at cocking.

For reference: about 100 Nm of elbow load and over 225 lb of shoulder pull is typical. Driveline reports lefties carry lower loads and better efficiency (16.1 versus 13.2 mph per unit of stress).

Fix

Pull several small levers instead of making one big change. Wake Forest's own conclusion was that small improvements across the whole delivery beat any single mechanical fix — their best prediction model only explained about 10% of the variance, so there is no formula. The published levers:

Arm more level with the shoulders at release
More real layback
Chest more stacked and closed at landing
Arm more turned over at landing
Hips peak earlier
Less sideways lean at release
More forward tilt at release

Or leave it

Load scales with velocity — a high-90s arm should read high. Stress per mph is the number that matters. Consider the counterexample: Dominican pre-pro pitchers carried 7.5% size-adjusted load with slower hands than US pitchers at 5.9%. High load with low output is the actual red flag.

See

A "safe" throwing program built on reduced effort — 60%, 70%, 80% intent days.

Why

What he feels and what his elbow takes are not the same thing. Throwing at 75–80% effort still produced 80 to 95% of full-effort elbow load. High school pitchers told to throw at 50% still produced 86% of their velocity and 75% of their max elbow load. Perceived effort drops a lot faster than actual effort does.

Fix

Manage his workload by throw count and total accumulated load, not by asking for a percentage. "Take something off" is a feeling, not a recovery plan.

Or leave it

Reduced effort still has a place for skill and command work. Just stop counting it as rest.

Link 13 · Arm

Forearm & wrist

The last place he has real control over how the ball spins — and the muscle group standing between the elbow load and the ligament.

Muscles & what they're doing

Palm-down turners (pronator teres, pronator quadratus) — shortening through release. The bigger one also doubles as an elbow protector.

Palm-up turners (supinator, biceps) — lengthening to control how fast the palm turns down. The balance between these two sets the spin axis.

Wrist flexors (inside forearm) — snap the wrist into release, plus they support the inside of the elbow.

Wrist extensors (outside forearm) — lengthening to control the wrist; the counterbalance.

Thumb-side forearm (brachioradialis) — bends the elbow and neutralizes rotation.

Test it

How far his wrist can tilt toward the thumb — this gates any arm-slot change
Palm-up and palm-down range and strength
Wrist flexion and extension strength, both sides
Grip endurance when he's tired

Load it

Wrist roller, both directions
Hammer rotations palm-up and palm-down; hammer tilts side to side
Band palm-down rotations at speed, for quickness not just strength
Plate pinches and towel hangs for grip
Wrist mobility work before attempting a slot change, not after it fails

See

Limited wrist tilt toward the thumb — and someone has suggested dropping his arm slot.

Why

Driveline's analysis of the league-wide move to lower slots is explicit: dropping the slot changes where the fingers sit on the ball at release, and it takes wrist tilt toward the thumb to keep the spin working through that new position. Without the wrist range, the slot change subtracts the pitch instead of reshaping it.

Fix

Build the wrist range and forearm strength first — or don't lower the slot. This is a prerequisite check, not an afterthought.

Or leave it

Not everyone should go low. Their stated profile for a good candidate: lots of wrist tilt available, average-or-below natural ride on the fastball, and command already in place.

See

He turns the hand over early, cuts the fastball, or gets under it at release.

Why

How the hand is turning at release sets the spin axis, which sets the angle the ball comes in on — so it moves both the shape and the location, not just the break. And which way the hand naturally wants to turn is treated as a built-in preference, not a technique choice.

Fix

Tread's cutting fix is environmental, not verbal: move him farther from the plyo wall, tape a target that forces the back shoulder to rotate through the target line, and let the arm find its own slot. Pair it with grip and seam work on a ball-flight unit.

Or leave it

Cut is a pitch. A natural cutting action is where a lot of cutters and sweepers come from. Take it to pitch design before you take it to the fix list.

See

Weak or quickly-fatiguing forearm; grip strength drops late in outings.

Why

Those muscles are the main active protection against the elbow being pried open. When they fatigue, the ligament takes a bigger share of a load that's already near its limit. This is why late-inning and late-season mechanics changes matter more than they look.

Fix

Direct forearm and wrist work plus honest workload management. It raises how long he can hold up; it does not lower the load.

Or leave it

No.

Link 14 · Last segment

Hand & fingers

Everything upstream exists to deliver this. How high he releases, how far off to the side, how far out toward the plate, and how the ball is spinning — those four things are what the hitter actually swings at.

Muscles & what they're doing

Finger flexors (running from the forearm into the fingers) — the last thing to touch the ball. Finger pressure at release sets how efficiently the ball spins.

Small hand muscles (lumbricals, interossei) — fine control of where the fingers sit on the seams.

Thumb muscles — thumb pressure quietly sets the ball's axis on most grips.

Finger extensors — lengthening to time the release. A rushed pattern here is one source of inconsistent spin.

Test it

Spin efficiency on each pitch, on a ball-flight unit
Release height, side, and extension — how consistent are they?
Grip strength and finger endurance
Hand size versus his grip choice — a real constraint, not a preference

Load it

Grip trainers, towel hangs, thick-bar carries
Finger extension bands to balance out all that gripping
Ball spin drills and seam-orientation work with immediate feedback
This is the one link where measurement beats coaching eyes by the widest margin

See

Low spin efficiency on a pitch that's supposed to ride or sweep; inconsistent finger pressure at release.

Why

Spin efficiency is a release-geometry problem, not an effort problem. The same delivery with different finger pressure produces a materially different pitch.

Fix

Ball-flight-driven pitch design — grips, seam orientation, seam-shifted wake work.

Or leave it

A spin-inefficient "dead" fastball is a bad four-seam and a promising cutter or slider. Change the label before you change the athlete.

See

Release point that moves around pitch to pitch.

Why

Some of that is on purpose. Driveline's command work found that variability in the arm near peak layback and in how the hand turns at release actually came with better command — elite arms adjust late to fix what happened earlier.

Fix

Chase consistency at foot landing, not at release. Their model is a funnel: varied entries converging on a consistent firing position at foot landing, then diverging again through late adjustments.

Or leave it

Yes — late adjustability is a skill. Drilling it out in pursuit of a "repeatable release" removes the mechanism that saves a pitch that started wrong.

Link 15 · Off the chain

Glove arm

The most over-coached limb in pitching. Two of the oldest cues in the sport — "equal and opposite" and "firm front side" — are both actively argued against by the labs, and there's published data on what the glove arm should do instead.

Muscles & what they're doing

Back of the glove shoulder and between the blades (posterior deltoid, rhomboids, mid trap) — shortening to open the glove arm out during cocking, then braking. An extended, opened-out glove arm at peak layback is what the data supports.

Glove-side lat and serratus — control the shoulder-blade disconnection that lets the throwing shoulder accelerate.

Glove-side side abs — link the front arm to chest rotation. This is where a glove "pull" either helps him turn or turns into linear drag.

Test it

How bent the glove elbow is at peak layback (more bent = worse, per the data)
How far the glove arm is opened out at peak layback
How consistent the glove shoulder is at foot landing, pitch to pitch
Does his head stay on line through release?

Load it

Prone horizontal abduction and face pulls — on the glove side too, not just the throwing side
Band-resisted glove-arm braking patterns
Rotational med-ball throws that finish with the glove side rotating, not stopping
Fix the back leg first — glove pulling is very often compensation for missing back-leg power

See

Glove yanks hard to the glove side; the head gets pulled off the target line with it.

Why

Pulling the glove often over-compensates for weak back-leg drive, and it makes the chest move forward in a line instead of rotating. Driveline's case against glove-blocking: it kills shoulder rotation speed — the biggest single contributor to a 90+ fastball — and drags the neck off line, which hurts consistency.

Fix

Fix the back leg first (links 02–03). Then teach the glove-side shoulder blade to disconnect from the throwing-side blade and let the glove decelerate over the front hip instead of stopping cold.

Or leave it

Some pullers throw hard and command it. If shoulder rotation speed is high and the head stays on line, the glove is doing its job in an unfamiliar-looking way.

See

Dead, passive glove arm; glove elbow tucked in tight and heavily bent at peak layback.

Why

Published data: a more bent glove elbow comes with more force on the throwing elbow, more force on the front of the throwing shoulder, and slower hips. The reverse is also true — a more opened-out glove arm at peak layback comes with faster chest rotation and a faster arm. An unused glove arm literally restricts how much the chest can turn.

Fix

Target a straighter, more opened-out glove arm at peak layback — then let it decelerate. Not "equal and opposite," which contradicts the whole principle that each segment slows down before the next one speeds up.

Or leave it

No — this is the rare glove-arm finding with real consequences on the throwing arm.

See

Glove shoulder height and chest lean vary pitch to pitch at the moment the foot lands.

Why

Driveline's command analysis found that consistency in the glove shoulder and chest lean at foot landing tracked with how far he misses by. Foot landing is the firing point — the last stable frame before everything spins.

Fix

Build repeatability into the foot-landing frame specifically, not the finish.

Or leave it

Weigh it against velocity: their framing is that velocity buys margin for error on command. A high-velocity arm can carry average command; a soft-tossing arm needs elite command. Spend your training time on whichever one he's short on.

Link 16 · Off the chain

Head, neck & eyes

The head is the reference point the whole delivery is aimed from. It's almost never the cause of anything — but it's a very good indicator.

Muscles & what they're doing

Deep front-of-neck muscles — holding; they keep the head on line against the rotational forces.

Sides of the neck (sternocleidomastoid, scalenes) — lengthening to control head rotation; over-recruited when the deep ones are weak.

Top of the shoulder into the neck (upper trap, levator) — often substituting for shoulder-blade muscles, which is what drags the neck into the delivery.

Test it

Chin-tuck hold time (deep neck endurance)
Head position at foot landing versus at release, on video
When he actually finds the target, relative to leg lift
Neck rotation range, both directions

Load it

Chin-tuck and deep neck holds
Multi-direction neck isometrics, or harness / Iron Neck work
Calm the upper trap down by strengthening serratus and mid-back instead
Target-acquisition timing drills

See

Head whips violently off line at release or in the follow-through.

Why

Usually just the cost of slowing down a fast-rotating chest — hard throwers' heads move. But when it happens early, the usual cause is glove-blocking pulling the neck around, which wrecks his visual reference.

Fix

Fix the glove arm (link 15), not the head. Cueing a still head in a high-velocity delivery adds tension without changing the cause.

Or leave it

A violent head finish after release does nothing. Distinguish "head moves while he's accelerating" from "head moves after the ball is gone" — the second one is free.

See

He finds the glove late — eyes get to the target well after the front foot has started down.

Why

The aiming solution is built during the stride. Finding the target late compresses the window in which he can still steer the delivery toward it.

Fix

Target-acquisition timing drills; often resolves once his head stops getting yanked by the glove.

Or leave it

Some deliberately "blind" deliveries — head down or turned late — are deception. If he commands it, it works.

Link 17 · The whole thing

Timing & the sequence

Not a body part — the relationship between all of them. Hips, then chest, then arm, then hand, each peaking later and faster than the one before, each slowing down to hand its speed forward. This is the whip, and it's where most "arm problems" actually live.

Muscles & what they're doing

The whole chain alternates between producing and braking. The glutes fire, the side abs fire, the lat fires, the cuff fires — but every one of them is also stopping the segment behind it. A pitcher who can produce but can't absorb will show a broken sequence no matter how strong he is.

That's why braking and holding work matters more for a thrower than raw pushing strength: the sequence is limited by his weakest brake, not his strongest engine.

Test it

The order and timing of peak speeds on the report
Med-ball throw speed versus vertical jump — production versus transfer
Drop-jump quality (how well he absorbs and returns)
Variability at foot landing versus at release — they should not be the same

Load it

Set up drills so the pattern happens on its own: step-back roll-ins, rocker drill, plyo wall work, tempo drills
Cue outward ("drive through the ground," "throw through the catcher's glove"), not inward ("load your back leg")
Train braking and holding, not just pushing
Med-ball throws in the actual sequence — low reps, full rest

See

Sequence out of order — chest peaks before hips, or the arm peaks before the chest.

Why

The whip only works if each segment slows down before the next one speeds up. Out of order means the arm is generating its own speed — which is exactly the profile that reads as high elbow load with unremarkable velocity.

Fix

Change the environment instead of adding cues. Driveline's stance is that weighted implements act as their own pitching coach, and that outward-focused cues beat body-part cues for full-body movements.

Or leave it

Rarely — sequence order is one of the few things close to a genuine universal.

See

The delivery doesn't look identical pitch to pitch, and the plan is to make it repeatable.

Why

Research found that skilled pitching is not less variability — it's better-organized variability. The chest and hips settle down before the foot lands; the shoulder doesn't settle down until peak layback. The base stays very repeatable while the arm carries the adjustments. Higher-velocity pitchers were better coordinated at release, not more frozen.

Fix

Train it in the right places: repeatability from the ground through foot landing, adjustability in the arm. Perfect repeatability isn't achievable and isn't the goal.

Or leave it

Yes — variability in the arm is a feature. It's the mechanism by which he saves a pitch that started wrong.

See

A hard thrower whose mechanics score poorly on efficiency.

Why

Driveline's own finding from 182 captures: pitchers above 87 mph looked less efficient than slower throwers. The harder you throw, the messier the mechanics tend to score. Efficiency and output aren't the same axis.

Fix

Judge on stress per mph, not on efficiency by itself.

Or leave it

Frequently. "Inefficient" at 96 is a completely different problem than "inefficient" at 84 — and only one of them is worth risking.

The programming layer

Which lift, for which quality, at which point in the year. Throwing lives at the very fast, very light end of the spectrum — which is exactly why you can't only train there.

Heavy-and-slow to light-and-fast, mapped to the delivery
Zone	How heavy, how many	Lifts	What it buys the delivery
Pure strengthmax strength	85–100% of the most he could lift once 1–5 reps · 3–5 sets · 3–5 min rest	Trap-bar deadlift, squat, rear-foot-elevated split squat, weighted chin-up, heavy hip thrust	Raises the ceiling everything else is a percentage of. Most under-built pitchers belong here, not in the med-ball room.
Heavy but faststrength-speed	55–80% of his max 3–5 reps, moved with intent	Trap-bar jump, clean pull or hang clean, heavy med-ball shotput, sled push	Back-leg force against a real load — the ground phase of the delivery.
Light and fastspeed-strength	30–55% of his max 3–6 reps · full rest	Jump squat, rotational and scoop med-ball throws, band-resisted rotation	Hip and chest rotation speed. This is the closest thing in the weight room to the delivery itself.
Bodyweight, maximum speedmax velocity	Bodyweight or lighter low volume · every rep high quality	Bounds, skaters, depth jumps, plyo ball work, long toss, weighted and underweight balls	How fast he can produce force — the block, the arm, and the whip.
Brakingeccentric / absorption	Heavy on the lowering, or very slow tempo	Nordics, reverse Nordics, box drops with a stick, landings from height, slow-lowering cuff work	The front-leg block and the arm's deceleration. The most commonly skipped zone, and the one that shows up as injury.

Train all three phases, because throwing uses all three

Every lift has a lowering phase, a turnaround, and a lifting phase — and the delivery uses all three in different places. Program them as emphasis blocks: braking first, then holding, then explosive, with load climbing and volume dropping across the blocks.

Map it: the front-leg block is braking into holding. The back leg is explosive. The arm's deceleration is pure braking. A pitcher who only trains the lifting phase has trained a third of his delivery.

Build it in the right order across the year

Off-season: build tissue and restore range → build pure strength → convert it to speed and throwing intent. In-season: cut the volume hard, keep the intensity — two full-body sessions a week is enough to hold what he built.

The common mistake is running a velocity block on a guy who never built the strength to express it. The other one is running a strength block in-season and wondering why his arm feels slow.

Arm care is a separate ledger

The Thrower's Ten has consistent evidence behind it: better shoulder blade stability, more range of motion, stronger and more durable rotator cuff, and better on-field performance. Run it year-round — high reps, light load, plus real slow-lowering work for the back of the cuff.

Understand what it is: armor, not mechanics. It raises how much he can tolerate. It does not lower the load his delivery produces — only the mechanical levers in the elbow section do that.

Med ball: the transfer tool

Rotational and scoop throws are the closest thing in the gym to the sequence itself. The drop-step side toss and the scoop side toss are the two highest-value variations. Program them like sprints: 3 to 6 reps, full rest, quality over volume.

Put them after the front-side core is competent. Med ball on top of a flared rib cage and an uncontrolled low back is exactly how oblique strains happen.

Train the athlete you have

A back-side, ground-loading athlete will express power in hinges, sled work, and lateral drives. A front-side, springy athlete will express it in squats, jumps, and reactive work. Both belong in the program — but the ratio should follow the athlete.

If a lift never clicks for someone who is otherwise strong and coachable, that's information about how he's built, not a character flaw.

Weighted balls, with the guardrails on

Driveline's position is that heavier and lighter balls are effective teachers — "their own pitching coach." Tread's guardrail is the other half: be very selective above 1 lb for high school and college, and avoid 2 lb entirely for youth, because at heavy weights the athlete tenses up protectively and produces the exact triceps-driven pushing pattern you're trying to remove.

Both are true. Use them as teaching tools, not as a velocity program.

The adaptation ledger

Seven situations where the compensation is the answer. If a pattern fits one of these, the right move is usually to build capacity around it rather than remove it.

Case 01

It's downstream of a physical limit

The compensation is his best available solution given the range and strength he has right now. Take it away without removing the limit and he just finds a worse one — usually further down the chain, usually in the arm. Fix the limit and the compensation dissolves on its own.

Case 02

It's how he's built, not a fault

Leg-lift height, back-leg depth, separation, arm slot, and which way his hand turns all track with how he naturally organizes movement. Coaching a pitcher across his own wiring is the mechanism the framework blames for avoidable oblique strains and arm injuries — and it's the most common reason a "correct" change never sticks.

Case 03

It buys pitch shape

Dropping the arm slot cost pitchers about 0.15 mph on average — and gained about 18 rpm on the four-seam, flattened the angle it comes in on, and cut elbow load about 4%. A "flaw" that trades a tick for deception and health is a good trade. Price it in results, not mph.

Case 04

It buys deception

Crossfire landings, quick tempo, short-arm actions, late target acquisition, unusual release windows. None of these show up on a biomechanics report as an asset, and every one of them shows up in the hitter's swing decisions. A delivery that looks clean and is easy to pick up is worse than one that isn't.

Case 05

It buys command

Velocity buys margin for error on command; below-average velocity demands elite command. If a compensation is what makes him repeatable at foot landing, it's paying for the thing that keeps him employed. Training time is finite — know which axis you're spending on.

Case 06

The stress per mph is already fine

Load scales with velocity, so a big number on a hard thrower is expected. Efficiency is the real diagnostic. The published bad trade is 28% more load for 1% more velocity. The published worst profile is high load with low output — Dominican pre-pros at 7.5% size-adjusted load with slower hands than US pitchers at 5.9%.

Case 07

He isn't the guy in the study

Arm slot data splits by level. Pros with lower slots showed lower elbow and shoulder load. High schoolers with lower slots showed higher elbow load. Same change, opposite bill. Don't transplant a big leaguer's compensation onto a sixteen-year-old and expect the same invoice.

The physics you're actually arguing with

Six ideas that explain most of what a report is telling you. No math required.

Force times time builds the delivery

How hard he pushes × how long he pushes = how fast he's movingJ = F · Δt = Δp

Speed comes from force applied over time against the ground. This is why coming off the rubber early and pushing straight up both cost velocity: one shortens the time, the other points the force the wrong way.

Stop the bottom, the top speeds up

Braking the hips against a firm front leg makes the chest spin fasterconservation of angular momentum

Same reason a car stops and the passenger keeps going. That's why how fast the front knee straightens predicts how fast the chest turns — and why a soft front side eats the energy instead of bouncing it up.

Twist is force times how far out it acts

The same arm speed costs more when the arm is in a worse positionτ = F × r

This is why position matters more than effort at the elbow. An arm off level, too much sideways lean, and a folded elbow at landing all lengthen or misalign the lever — so the same arm speed writes a bigger check.

Longer runway, lower peak

Slow the arm down over a longer arc and the peak force dropsaverage force = momentum change ÷ time

This is exactly why more real layback comes with less elbow load. Fake layback shortens the arc while keeping the look — so he pays the peak force and doesn't collect the velocity.

The chain is a handoff, not a pile-on

Hips → chest → arm → hand, each one slowing down to pass it forwardproximal-to-distal sequencing

Every segment has to slow down to hand its speed to the next one. That's why "equal and opposite" fails as a cue, and why a broken sequence shows up as elbow load: the arm is generating what it should have been handed.

The hand is where you get paid

Release height + release side + extension + spin axis = what the hitter seesapproach angle

Everything upstream exists to serve four numbers at the hand. A mechanical "flaw" that improves any of them isn't a flaw — it's pitch design that happened by accident.

Sources

Coaching sources are cited for their published frameworks and thresholds; peer-reviewed work is cited for the numbers.

Driveline — How We Interpret Biomechanics Reports
Driveline — Biomechanics Rewind: A Look at the Numbers
Driveline — Pitching Assessments and Changing Mechanics
Driveline — Making Movement Changes in the Weight Room
Driveline — A Different Model for Cueing Pitching Mechanics
Driveline — Why We Don't Teach Equal and Opposite (or Firm Front Side)
Driveline — The Interaction of Biomechanics and Command
Driveline — Pitchers Are Going Low — And For Good Reason
Tread Athletics — How to Fix a Pushing Arm Action: 7 Causes and Solutions
Tread Athletics — Problem Solving Your Lower Half Pitching Mechanics
Baseball Performance Center — Remote pitching assessment framework (arm action, drive-leg efficiency, lead-leg block)
Wake Forest Pitching Lab — Research index (Nicholson, Bullock, Waterman et al.)
Wake Forest — Association between pitching velocity and elbow varus torque, Braz J Phys Ther (298 pitchers)
Wake Forest — Differences in Pitching Kinetics and Kinematics During Various Effort Level Pitching, Wolf, Kinney, Waterman, Bullock, Nicholson (2025)
Markerless capture — Predicting elbow valgus torque from upper extremity kinematics
Bullock, Nicholson et al. — Baseball pitching biomechanics in relation to pain, injury, and surgery: a systematic review
Frontiers — Kinematic and kinetic comparison: Dominican Republic vs. United States pre-professional pitchers
American Baseball Biomechanics Society — About / standardization mission (founded 2020; Fleisig, Nakamura, Stewart, Shapiro, Plummer, Solomito, Slowik, Oliver et al.)
ASMI / Diffendaffer, Bagwell, Fleisig et al. — The Clinician's Guide to Baseball Pitching Biomechanics, Sports Health
Fleisig et al. — Kinematic Parameters Associated With Elbow Varus Torque in Elite Adult Baseball Pitchers (523 pitchers)
Pitching Biomechanics Normative Values and Kinetic Differences by Competition Level
Kinematic and Kinetic Comparisons of Arm Slot Position Between High School and Professional Pitchers
The Effect of Trunk and Lower Body Mechanics on Fastball Velocity, SportRxiv
Skilled pitching is not less joint variability but better-structured joint variability, SportRxiv
Lumbopelvic-hip Control, Upper Extremity Joint Moments, and Drive Leg Ground Reaction Force in Adolescent Pitchers, IJSPT
Decreased Hip Internal Rotation Increases the Risk of Back and Abdominal Muscle Injuries in Professional Baseball Players (258 player-seasons)
Relationship of Glove Arm Kinematics With Established Pitching Kinematic and Kinetic Variables
Gluteus Medius and Scapula Muscle Activations in Youth Baseball Pitchers, J Strength Cond Res
Jobe, Moynes, Tibone, Perry — An EMG analysis of the shoulder in pitching
Comparison of teres minor and infraspinatus muscle activation (deceleration-phase roles)
Effect of Increased Scapular Internal Rotation on Glenohumeral External Rotation and Elbow Valgus Load
Rehabilitative and Preventive Effects of the Thrower's Ten Program in Overhead Athletes: A Systematic Review
NSCA — CSCS program-design framework; force–velocity and periodization principles
ActionTypes / motor preferences — Aerial vs. Terrestrial pitchers and Cracking the code of motor preferences (Hippolyte & Théraulaz)
The Contribution of Lower-Body Kinematics to Pitching and Hitting Performance (OpenBiomechanics Project)