Using light weights for arm exercises can make your arms slightly more muscular, but using light or heavy weights for leg exercises doesn’t change leg muscle size in young women who haven’t trained before.

Scientific Claim

Lower-load resistance training (30–50% 1RM) increases fat-and-bone-free mass in the upper limbs of untrained young women, while no change in leg muscle mass was observed with either load.

Original Statement

“Dual-energy X-ray absorptiometry showed no change in leg fat-and-bone-free mass (FBFM) for either condition, and an increase in only LL arm FBFM.”

From study:Higher- and lower-load resistance exercise training induce load-specific local muscle endurance changes in young women: a randomised trial.

Evidence Quality Assessment

Claim Status

appropriately stated

Study Design Support

Design supports claim

Appropriate Language Strength

probability

Can suggest probability/likelihood

Assessment Explanation

RCT design supports causation, but small sample and lack of full methodological detail warrant cautious language. 'Increases' is acceptable but should be probabilistic.

More Accurate Statement

“Lower-load resistance training (30–50% 1RM) is likely to increase fat-and-bone-free mass in the upper limbs of untrained young women, while no change in leg muscle mass is observed with either load.”

Evidence from Studies

Supporting (1)

Higher- and lower-load resistance exercise training induce load-specific local muscle endurance changes in young women: a randomised trial.

Randomized Controlled Trial

Human

2022 Dec 1

This study found that lifting light weights for the arms made the arm muscles bigger in young women, but lifting light or heavy weights for the legs didn’t change leg muscle size — exactly what the claim says.

Contradicting (0)

No contradicting evidence found

Source Study

Higher- and lower-load resistance exercise training induce load-specific local muscle endurance changes in young women: a randomised trial.

Score: 52

DOI: 10.1139/apnm-2022-0263

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