Even though muscles got bigger, the actual muscle fibers didn’t get thicker or change type—so the growth might be due to other factors like fluid or connective tissue.

Scientific Claim

Neither low-load nor high-load resistance training is associated with changes in muscle fiber cross-sectional area or fiber type composition in resistance-trained adults after 9 weeks of training.

Original Statement

“However, this was not accompanied by changes at the myocellular level, with no observed differences in fCSA and fiber type composition.”

From study:Divergent Strength Gains but Similar Hypertrophy After Low-Load and High-Load Resistance Exercise Training in Trained Individuals: Many Roads Lead to Rome.

Evidence Quality Assessment

Claim Status

overstated

Study Design Support

Design cannot support claim

Appropriate Language Strength

association

Can only show association/correlation

Assessment Explanation

The abstract reports no changes, but without full methodological details (e.g., biopsy sampling protocol, statistical power), the claim cannot be confirmed as definitive.

Evidence from Studies

Supporting (1)

Divergent Strength Gains but Similar Hypertrophy After Low-Load and High-Load Resistance Exercise Training in Trained Individuals: Many Roads Lead to Rome.

Randomized Controlled Trial

Human

2025 Sep 1

Contradicting (0)

No contradicting evidence found

Source Study

Divergent Strength Gains but Similar Hypertrophy After Low-Load and High-Load Resistance Exercise Training in Trained Individuals: Many Roads Lead to Rome.

Score: 25

DOI: 10.1152/japplphysiol.00353.2025

Similar Assertions

Even though muscles get bigger after 10 weeks of weightlifting, the individual muscle fibers don’t necessarily get thicker — the growth might come from how the fibers are arranged, not from each one swelling up.

82%

There are only a few small, short studies on this topic, and many didn’t even track whether people stuck to their workout plans — so we can’t trust the results very much.

82%

Whether you use light or heavy weights, your muscles can grow about the same amount if you train hard enough—both methods work for building muscle size.

79%

We just don’t know yet if light or heavy weights make muscles grow better — the results could swing either way in future studies, so we need more research.

79%

Doing light weightlifting with a band that restricts blood flow for six weeks can make both slow and fast muscle fibers in older people grow bigger by about 20%, even without heavy lifting.

78%