Leg Press vs Leg Extension: They Don’t Build the Same Quad

Twenty-eight trained lifters each trained one leg with leg press, the other with leg extension. Same person. Same effort. Same eight weeks. The front of the quad — the muscle that gives your leg that straight-on pop — grew 8.9% with extensions but only 4.7% with leg press.

The outer quad — the sweep you see from the side — went the other direction. 8.7% growth with leg press, but only 2.9% with extensions.

Neither exercise skipped a region: the leg-press leg still added 4.7% at the front, the extension leg 2.9% at the side. But each exercise grew a different region of the same muscle more. Not different people responding differently. The same person's quad grew most in different places depending on which exercise that leg performed.

The question "which is better?" has no answer. Because the question is wrong. To fully develop the quad, the authors conclude, it would seem both are needed. Each builds a different part of it more.

What It Costs to Pick Just One

That paradox has a price you can calculate right now.

If leg press is the only quad exercise in the program — and for many lifters trained on the "just squat" advice, it is — the front quad grew about 53% as much as it did on the extension leg (4.7% against 8.9%). Roughly half, for the muscle that makes your quads look developed from the front.

The advice that enabled this gap is the most repeated line in every gym, every forum, every training video. "Compounds cover everything." Burke's data puts a number on what that belief costs, for the one compound it tested. The leg press built the outer quad well. At the front, it grew about half as much as the extension.

And the exercise that fills the gap? The one many lifters skip every single leg day.

The Exercise You Were Told to Avoid

Leg extensions have been called "bad for your knees" for at least two decades. The advice has been so persistent that an entire generation of lifters walks past the extension machine without a second thought.

Burke's data found that the exercise most lifters avoid grew the front quad nearly twice as fast as leg press. The region the leg press grew least responds most to exactly the exercise the gym has been telling people to skip.

And the knee concern? Physiotherapy clinics use leg extensions for knee rehabilitation. The exercise avoided for safety in the gym is prescribed for recovery in the clinic.

Two ironies. The exercise avoided for safety is the one the front quad needs. The exercise lifters fear is the one clinicians trust. But quads are only half the story Burke's study tells.

Your Calves Might Not Be Genetic

Burke's team didn't just compare quad exercises. They compared calf exercises too. And the finding hits a different nerve entirely.

Seated calf raises (bent knee) versus a straight-leg toe press, done on a leg press machine with the knee straight. The main calf muscle — the one that gives your calf its visible shape — grew more with the straight-leg exercise. How likely is it, by the study's statistical model, that the straight leg really grew it more? 99.1%.

For that muscle, the seated calf raise machine bolted to the floor of nearly every gym was the weaker choice.

For anyone who has been doing seated calf raises for years and blaming genetics for calves that won't grow, Burke's data offers a different explanation. Maybe the genetic ceiling hasn't been reached. Maybe the exercise just never tested it.

That reframe changes the calf conversation. The question shifts from "are calves genetic?" to "have I actually trained them with the right exercise?" If this pattern holds for quads and calves within one study, does it hold for other muscles too?

Four Research Teams, One Principle

Four independent research teams answered yes.

Hip thrusts, squats, and deadlifts each grow different parts of the glute — the same split Burke found in the quad. That finding held across 12 studies and 318 participants [1].

The chest told the same story. Flat bench favored the lower portion. Incline favored the upper [2]. Twenty-three studies, same pattern.

And the effect is exercise-driven, not simply a function of which part of the muscle stretches more — confirmed across another 12 studies [3].

Which exercise you pick reshapes the growth map. But how deep you go on each rep? A review of 24 studies on range of motion found the measured advantage for full reps was 2.8% — a difference no mirror or tape measure would catch.

Quads, calves, glutes, chest. Four muscle groups, four independent research teams, convergent findings. Exercise selection can shift where a muscle grows. But is the pattern as airtight as it looks?

Where the Evidence Gets Messy

Earp and colleagues published a 2023 study that found the opposite pattern for the front quad — but in untrained participants. Their multi-joint movement actually favored front quad growth. Burke used trained lifters. Earp used beginners.

That matters — the split-quad effect may depend on training experience, or on the exercise: Earp's multi-joint movement was a one-leg Smith machine squat, which Burke's team suggests may have changed how the muscles were recruited. For someone just starting out, the regional difference might not apply yet. Burke's finding comes from lifters who already have a training base; the authors see no logical reason it would differ in other groups, but this study did not test them.

One of Burke's own calf findings didn't hold up. The smaller calf muscle initially appeared to favor straight-leg raises, but when the researchers re-ran the analysis on only the legs that did leg extensions, that advantage disappeared. That specific finding is genuinely uncertain.

The chest evidence carries a caveat too — it measured muscle activation during exercise, not actual growth over time. A strong signal in one session doesn't guarantee what happens after eight weeks of training.

Burke's quad and main calf findings measure real thickness changes over eight weeks. The satellite evidence is convergent but not identical in quality. The strong evidence feels stronger when the weaker evidence is visible beside it.

A Map for Every Muscle

Burke's study started as a comparison between two leg exercises. It ends as a lens for the entire program.

The principle that emerged, for the quad: to fully develop it, the authors conclude, it would seem a combination of exercises is needed. Burke's data showed the front quad responded more to extensions than to press. The outer quad responded more to press than to extensions. The main calf muscle responded more to straight-leg work than to seated. For the calves, the authors drew the opposite lesson: the straight-leg exercise seemingly developed all three calf muscles, and whether the seated raise adds anything is unclear.

The broader application: if this pattern holds for quads, glutes, and chest — and the converging evidence suggests it does — then a single exercise per muscle, no matter how heavy, may grow some parts of that muscle less than a different exercise would.

Burke's team studied 28 trained adults, averaging 20.7 years old, over eight weeks at two sessions per week. Each participant trained one leg with leg press and the other with leg extension, each leg also doing one of the two calf exercises — a design that controls for genetic and lifestyle differences between people. The technician who measured muscle thickness and the statistician who analyzed the data were both blinded to which leg received which exercise.

The data says what it says. Exercise selection changes where muscle grows. The lifter who was looking for a winner between leg press and leg extension found something more useful.

For the full quad, both exercises appear to be needed. The remaining question isn't about legs — it's about every muscle group in the program.