Whether you train both legs together or one at a time, your thigh muscles grow about the same amount after 12 weeks of heavy lifting.

Scientific Claim

Twelve weeks of progressive heavy resistance training is associated with a 14% increase in quadriceps muscle cross-sectional area (CSA) in bilateral-trained individuals and an 11% increase in unilateral-trained individuals, with no statistically significant difference between the two training methods.

Original Statement

“The relative increases of 14±12% (P<0.001) and 11±6% (P<0.001) recorded for the CSA in all BIL and UNIL trained subjects did not differ significantly from each others.”

From study:Neuromuscular adaptations during bilateral versus unilateral strength training in middle-aged and elderly men and women.

Evidence Quality Assessment

Claim Status

overstated

Study Design Support

Design cannot support claim

Appropriate Language Strength

association

Can only show association/correlation

Assessment Explanation

The study uses 'leads to' and 'produce' in the abstract, but without confirmed randomization, causal language is inappropriate. Only associations are supported.

Evidence from Studies

Supporting (1)

Neuromuscular adaptations during bilateral versus unilateral strength training in middle-aged and elderly men and women.

Randomized Controlled Trial

Human

1996 Sep

Both ways of lifting weights—using both legs together or one leg at a time—made people’s thigh muscles grow by about the same amount after 12 weeks, even though they got stronger in different ways.

Contradicting (0)

No contradicting evidence found

Source Study

Neuromuscular adaptations during bilateral versus unilateral strength training in middle-aged and elderly men and women.

Score: 46

DOI: 10.1046/j.1365-201x.1996.523293000.x

Similar Assertions

When people train one leg at a time, that leg gets much stronger than the other leg, even if the other leg didn’t do any training.

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Doing leg exercises with both legs at the same time for 12 weeks makes you stronger at lifting with both legs together, while doing them one leg at a time makes you stronger at lifting with each leg separately.

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Even though the guys doing the most workouts looked like they might have grown a little more, the difference wasn’t big enough to say for sure that more sets = more muscle.

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Doing a lot more leg workouts—over 50 sets a week—doesn’t make your thigh muscles grow bigger than doing 20–40 sets a week, even if you train for 12 weeks.

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Whether you use light or heavy weights, your muscles can grow about the same amount if you train hard enough—both methods work for building muscle size.

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