Heavy or Light, Your Muscles Still Grow (If You Go All Out) - Turns Out, Your Gains Are All About You!

Overview

Paper Summary › Explain Like I'm Five › Conflicts of Interest › Identified Limitations › Rating Explanation › Good to know › Topic Hierarchy › File Information ›

Paper Summary

Paperzilla title

In healthy young men, this study found that muscle growth from resistance training is largely consistent within each person and unaffected by whether they lift heavy or light weights, as long as they train to muscle fatigue. While muscle protein synthesis rates were similar between loads, they decreased over the 10-week training period despite increasing training intensity. This suggests individual biological factors, not just the load, dictate how much muscle someone gains.

Explain Like I'm Five

When you lift weights until you're super tired, it doesn't matter much if the weights are heavy or light your muscles grow about the same. It's like your body has its own personal muscle-growing plan that largely stays the same for all your body parts.

Possible Conflicts of Interest

The corresponding author (S. M. Phillips) reported receiving grants, research contracts, and personal fees from various organizations, including the US National Dairy Council, Dairy Farmers of Canada, Roquette Freres, Nestle Health Sciences, and Myos, all of which have commercial interests related to nutrition and muscle health. The study also acknowledged a donation of whey protein isolate by Leprino Foods. This suggests potential conflicts of interest, especially given the context of a muscle hypertrophy study often linked to protein intake.

Identified Limitations

Limited Generalizability

The study involved only healthy young males (n=20), which limits the generalizability of the findings to other populations, such as females, older adults, or individuals with different health statuses.

Reduced Sample Size for MyoPS

Data for myofibrillar protein synthesis (MyoPS), a key mechanistic outcome, was only available for 11 out of the 20 participants, which reduces the statistical power and confidence in these specific findings.

Unilateral Design and Cross-Limb Effects

Although a strength for within-subject comparisons, the unilateral training design could involve a 'cross-education effect' where training one limb might influence the strength (and potentially hypertrophy) of the contralateral limb, possibly masking some load-specific differences.

Limited Biopsy Location

Muscle biopsies for detailed fibre-specific analysis were exclusively taken from the vastus lateralis (leg), preventing direct fibre-level comparisons of training adaptations between the upper and lower limbs.

Fibre Circularity Exclusion

The analytical exclusion of irregularly shaped muscle fibres (circularity cut-off >0.80) may omit important morphological adaptations that occur with resistance training, potentially underestimating certain aspects of hypertrophy.

Rating Explanation

The study is well-designed with a strong within-subject methodology and multiple, robust measures of hypertrophy. Its key finding, that load doesn't determine hypertrophy when training to fatigue, is significant for exercise science. While limited to healthy young males and having a reduced sample size for MyoPS, the limitations are acknowledged, and the declared conflicts of interest are noted.

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Topic Hierarchy

Domain: Health Sciences

Field: Health Professions

Subfield: Physical Therapy, Sports Therapy and Rehabilitation

File Information

Original Title: Resistance training load does not determine resistance training-induced hypertrophy across upper and lower limbs in healthy young males

Uploaded: January 14, 2026 at 11:44 AM

Privacy: Public