The Exercise You're Doing Isn't the One You Think

Two people run identical programmes on paper and get different results. The usual explanations are genetics, effort, or recovery. Often it's something more boring: they weren't training the same muscles.

#Resistance profiles

Every exercise has a resistance profile — how the external moment arm changes through the range of motion, which determines where the movement is hardest.

A barbell curl is hardest at 90° of elbow flexion, where the forearm is horizontal and the moment arm is longest. It's nearly free at the top and bottom. A cable curl with the right setup is roughly constant. A preacher curl is hardest near full extension.

Meanwhile every muscle has an active length-tension relationship — a length at which it produces peak force, with force falling off either side as actin-myosin overlap becomes sub-optimal.

Where the resistance profile overlaps the length-tension relationship determines which region of the muscle gets loaded hardest. That's the mechanistic basis of regional hypertrophy, and it's why "just pick a movement and take it to failure" is incomplete advice.

#Three exercises that don't do what they're assigned

The squat and rectus femoris. The quadriceps has four heads. Three are pure knee extensors. The fourth, rectus femoris, also crosses the hip — it's a hip flexor. During a squat the hip flexes, which shortens rectus femoris at one end while the knee lengthens it at the other. The net length change is small, so it's poorly loaded. You can squat heavy for years with an underdeveloped rectus femoris, and the fix is a leg extension performed leaning back, which extends the hip and lengthens it properly.

Pushdowns and the triceps long head. The long head crosses the shoulder joint. With the arm at your side it's already partly shortened, so a pushdown trains the lateral and medial heads well and the long head — the largest of the three — poorly. It's only genuinely stretched overhead. If your triceps development has stalled and you only do pushdowns, that's the reason.

Dumbbell laterals at the bottom. With the arm hanging at your side, the moment arm on the medial deltoid is essentially zero — the weight is directly below the joint. The first third of the movement is nearly unloaded. A cable set up so the line of pull crosses behind the body loads the stretched position, which is exactly where the mechanical tension does most.

#The stretched position is the free variable

At long muscle lengths, sarcomeres sit past optimal overlap and the force deficit is carried by passive tension in titin. Titin isn't just an elastic element — strain-dependent unfolding of its immunoglobulin domains exposes binding sites for signalling proteins, making it a genuine mechanosensor. Training at long lengths also biases adaptation toward adding sarcomeres in series.

The applied finding, from meta-analysis by Wolf, Androulakis-Korakakis and colleagues: lengthened partials match or beat full range of motion for hypertrophy, and with one exception every study comparing muscle lengths found longer produced more growth.

So the selection rule becomes simple. For each muscle, pick one movement that loads it hard in the stretched position, and one that loads a different part of the curve:

• Overhead extension over pushdown
• Incline curl over standing curl
• Seated leg curl over lying (hip flexed = longer hamstring)
• Deep dumbbell press or fly over flat barbell
• Cable lateral behind the body over dumbbell

#Machines aren't the inferior option

The free-weight-supremacy position is mostly cultural. For hypertrophy specifically, machines and cables are often superior, because they let you load the stretched position without stability being the thing that ends the set.

Free weights win on transfer to sport, on loading the whole body efficiently, and on strength expression. Those are real advantages — they're just not hypertrophy advantages.

#Two per muscle

More exercises is variety, and variety costs you the ability to track progression. If you rotate through six chest movements you'll never know whether any of them is improving.

One stretch-loaded primary, one covering a different part of the curve, tracked for months. That's the whole thing.

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This is one piece of a larger system. The full protocol — every mechanism, every dose, every source tier, and an append-only record of everything it has gotten wrong — is at /protocol. The training system this comes from is at /protocol/hypertrophy, and the free tracking spreadsheet is here.