Doing leg extensions (kicking your leg out while sitting) makes the front thigh muscle right above your knee grow more than doing leg presses (pushing a heavy platform with both legs).

Scientific Claim

Single-joint leg extension exercises are likely to produce greater hypertrophy in the rectus femoris muscle compared to multi-joint leg press exercises in trained young adults after 8 weeks of training, due to greater isolated activation of this bi-articular muscle.

Original Statement

“Point estimates for the rectus femoris outcomes favored the single-joint exercise intervention with posterior probabilities ranging from 0.910 ≤ P ≤ 0.990.”

From study:Exercise Selection Differentially Influences Lower Body Regional Muscle Development

Evidence Quality Assessment

Claim Status

appropriately stated

Study Design Support

Design supports claim

Appropriate Language Strength

probability

Can suggest probability/likelihood

Assessment Explanation

The study design (RCT) supports causal inference, but the authors used probabilistic Bayesian posterior probabilities (not p-values), so 'likely' is appropriate. The claim correctly limits scope to rectus femoris in trained young adults.

Evidence from Studies

Supporting (1)

Exercise Selection Differentially Influences Lower Body Regional Muscle Development

Randomized Controlled Trial

Human

The study found that doing leg extensions (kicking out just your knee) made the front thigh muscle called rectus femoris grow more than doing leg presses (pushing with both knee and hip), because leg extensions focus only on the knee.

Contradicting (0)

No contradicting evidence found

Source Study

Exercise Selection Differentially Influences Lower Body Regional Muscle Development

Score: 61

DOI: 10.1007/s42978-024-00299-4

Similar Assertions

Doing leg extensions makes the front thigh muscle grow more evenly along its length than doing squats, which don’t stimulate that muscle as much.

84%

Pushing a heavy leg press machine makes the outer part of your thigh muscle grow more than doing leg extensions, because it puts more overall stress on that part of the muscle.

81%

Doing leg extensions with drop sets (going to failure, then lowering the weight and going again) makes the front part of your thigh muscle grow more than doing regular sets, but only in the upper and middle parts—not the bottom or the side muscles.

78%

Doing leg extensions with your hip bent at 40 degrees instead of 90 degrees probably makes the front thigh muscle (rectus femoris) grow more in guys who haven’t lifted weights before.

77%

If you’re already experienced with weightlifting and train your legs twice a week for 8 weeks with hard sets, your muscles will grow whether you take short breaks between reps or not.

77%