Heavy vs Light Weights
A 9-week trial shows low-load training produce nearly identical muscle growth when both are taken to failure.
A new study out of Mississippi State University tracked 17 recreationally trained young men over nine weeks of resistance training and found that lifting heavy or light produced nearly identical muscle growth. The only edge heavy training had was strength gains. Hormones? Barely moved either way.
Aim
Researchers wanted to know whether training load changes how much muscle you build and how your hormones respond. Specifically, they compared lifting at 85% of your one-rep max (1RM) against lifting at just 30% 1RM, both taken to failure, over nine weeks of full-body training.
Methods
Seventeen recreationally trained males with an average age of 20 years were split into two groups: a high-load group (85% 1RM, n = 8) and a low-load group (30% 1RM, n = 9). Both groups trained three days per week for nine weeks, performing three working sets per exercise to failure. The program included back squat, deadlift, bench press, T-row, bicep curls, and skullcrushers.
Muscle thickness was measured via ultrasound at the biceps, triceps, chest, hamstrings, and quads at baseline and every three weeks. Salivary testosterone and cortisol were collected first thing in the morning and immediately after training sessions. Predicted 1RM was tested at the start and end of the program.
Results
Both groups got bigger. Muscle thickness increased significantly over time across nearly every site measured, with no meaningful difference between groups. The one exception was the triceps, where the high-load group showed earlier and more consistent growth, with significant increases from week three onward compared to no clear change in the low-load group.
For strength, the high-load group came out ahead. Relative strength improvements in the squat, deadlift, and bicep curl were significantly greater in the heavy group, even after accounting for baseline differences.
On the hormone side, neither testosterone nor cortisol changed in a statistically meaningful way over the nine weeks, either at rest or in response to training sessions. Both groups showed a modest drop in testosterone immediately after exercise, though this did not reach significance. The authors noted this pattern could reflect androgen receptor uptake rather than a true decline, since the study measured free testosterone via saliva and resistance training is known to increase receptor activity.
Key Takeaways
Training to failure matters more than the weight on the bar when it comes to muscle growth
Heavy loading (85% 1RM) produced greater relative strength gains in the squat, deadlift, and bicep curl
The triceps showed a notable advantage for the heavy group, growing faster and more consistently
Cortisol and testosterone stayed stable across both groups, suggesting both training approaches were similarly manageable from a recovery standpoint
The drop in post-exercise testosterone seen in both groups may reflect androgen receptor binding rather than a hormonal problem
Results apply to recreationally trained males only; women and elite athletes may respond differently
The study was small, which limits how confidently you can apply the findings. A larger sample and longer monitoring window, particularly for hormonal tracking, would strengthen the conclusions. Still, this adds to a growing body of evidence that for building muscle, effort and consistency are the key variables, not whether you are grinding heavy singles or doing high-rep sets.
Reference
Bello, M.L.; Arent, S.M.; Gillen, Z.M.; Smith, J.W. Muscle Hypertrophy, Strength, and Salivary Hormone Changes Following 9 Weeks of High- or Low-Load Resistance Training. J. Funct. Morphol. Kinesiol. 2026, 11, 17. https://doi.org/10.3390/jfmk11010017
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