Lifting heavy weights makes your legs much stronger than lifting light weights, but for your arms, both heavy and light weights make you about equally stronger.

Scientific Claim

Higher-load resistance training (80–90% 1RM) leads to greater increases in leg strength than lower-load training (30–50% 1RM) in untrained young women, but no significant difference in upper-body strength gains between loads.

Original Statement

“Strength increased more in the HL compared to LL leg (P < 0.01), but similar increases in strength were observed between upper body conditions (P = 0.46).”

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 causal inference, but small sample and unknown blinding limit confidence. 'Leads to' is appropriate but should be probabilistic per EBM guidelines.

More Accurate Statement

“Higher-load resistance training (80–90% 1RM) is likely to lead to greater increases in leg strength than lower-load training (30–50% 1RM) in untrained young women, but no significant difference in upper-body strength gains is observed between loads.”

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 heavy weights made women’s legs stronger than lifting light weights, but for the arms, both heavy and light weights worked just as well — 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

Similar Assertions

If you lift heavy weights, you get better at doing more reps with heavy weights; if you lift light weights, you get better at doing more reps with light weights — your muscles adapt specifically to the weight you use.

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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.

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When lifting weights with your arms, whether you use heavy or light weights, you get about the same improvement in how many reps you can do with both heavy and light weights.

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Lifting heavier weights (fewer reps) leads to bigger strength gains than lifting lighter weights (more reps), even if both are done until exhaustion.

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To get stronger, it matters more how heavy the weight is than whether you push to your absolute limit—lifting heavier weights makes you stronger, no matter if you stop short of failure.

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