The Study
Muscle Hypertrophy, Strength, and Salivary Hormone Changes Following 9 Weeks of High- or Low-Load Resistance Training
This study watched two groups of guys lift weights differently for 9 weeks and saw that both got stronger and bigger, but the heavy-lifters got a bit stronger. But since we don’t know if they were randomly assigned, we can’t say one way caused the difference — it might just be luck or other stuff.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
Two groups lifted weights for 9 weeks—one used heavy weights, one used light weights—but both lifted until they couldn’t do another rep. Both got stronger and bigger muscles, but the heavy group got much stronger in lifts like squats.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 562 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes—light weights can build muscle just as well as heavy ones if you train hard, but heavy weights are better for getting stronger in big lifts.
- 2Both groups grew similar muscle in arms, legs, and thighs—except triceps grew faster with heavy weights.
- 3Pectorals didn’t grow in either group.
- 4Heavy group got 20% stronger in 1-RM lifts (exact number not given).
- 5Hormones didn’t change.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Journal of Functional Morphology and Kinesiology
Year
2025
Authors
Marissa L. Bello, S. Arent, Zachary M. Gillen, JohnEric W. Smith
Related Content
Claims (10)
People who have not previously trained may experience different muscle growth patterns from those who have been training regularly, when exposed to the same exercise routines.
When resistance training is performed until muscle fatigue is reached, lifting light weights and lifting heavy weights result in the same amount of muscle growth.
When people lift weights until they can no longer complete another repetition, the amount of muscle growth is similar whether they use light, moderate, or heavy weights.
For people who train casually, lifting lighter weights more times and lifting heavier weights fewer times produce similar muscle growth if the total work done is the same, but the heavier-weight approach might lead to slightly stronger performance.
Performing strength exercises until muscle fatigue, with 8 to 12 repetitions per set, results in an increase in muscle size in people who have not previously trained regularly.
To stimulate muscle growth, resistance exercises must be performed with adequate duration and precision to activate most of the motor units within the muscle.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.