Heavy or Light Weights: Which Builds Muscle Better?
Muscle Hypertrophy, Strength, and Salivary Hormone Changes Following 9 Weeks of High- or Low-Load Resistance Training
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
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.
Surprising Findings
The pectoralis major showed no significant hypertrophy despite other muscles growing.
Most people assume chest exercises like bench press automatically build chest muscle—this study says otherwise, even with training to failure.
Practical Takeaways
Use light weights (30% 1-RM) for muscle growth if you’re injured, traveling, or hate heavy lifting—just train to failure and match volume.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
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.
Surprising Findings
The pectoralis major showed no significant hypertrophy despite other muscles growing.
Most people assume chest exercises like bench press automatically build chest muscle—this study says otherwise, even with training to failure.
Practical Takeaways
Use light weights (30% 1-RM) for muscle growth if you’re injured, traveling, or hate heavy lifting—just train to failure and match volume.
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 (6)
If you lift light weights for more reps or heavy weights for fewer reps—but do the same total amount of work—you’ll grow your muscles just as much either way.
If you lift weights until you can’t do another rep—whether you use heavy weights or light ones—you’ll end up with about the same muscle growth after nine weeks, as long as you’re putting in the same effort and number of reps.
When guys who work out a little bit lift heavy weights (85% of their max), their triceps muscles grow faster and more reliably than when they lift light weights (30% of their max)—so how heavy you lift might change when your muscles start getting bigger.
If you lift heavy weights (85% of your max) instead of light ones (30% of your max) for nine weeks, you’ll get stronger on exercises like squats and deadlifts—even if your muscles don’t grow any bigger than if you’d lifted light weights.
Doing weight training either heavy or light until you can't do another rep for nine weeks doesn't change your hormone levels in your saliva, and that's okay—your muscles can still get stronger and bigger even if your hormones don't budge.