The Claim
Eight weeks of resistance training produces significant hypertrophy of type IIa and IIx muscle fibers in young untrained men, with no significant changes in type I fiber size or overall fiber type distribution.
What the research says
Supports is higher
Support is ahead, but a single strong opposing study can change this.
These are independent scores, not a percentage. Higher-grade studies count more, so a single strong opposing study can outweigh several weaker ones.
When young men who don't normally exercise do eight weeks of weight training, their fast-twitch muscle fibers get bigger, but their slow-twitch fibers stay the same size and the overall mix of muscle types doesn't change.
See the scientific wording
Eight weeks of resistance training produces significant hypertrophy of type IIa and IIx muscle fibers in young untrained men, with no significant changes in type I fiber size or overall fiber type distribution.
What the research says
1 studyStudy: Fasted‐state skeletal muscle protein synthesis after resistance exercise is altered with training
The study did the same type of exercise training as the claim and found exactly what the claim said: fast-twitch muscle fibers grew bigger after 8 weeks, while slow-twitch fibers didn't change.
Score breakdown, mechanism chain, raw evidence, ideal studies needed & 1 supporting studies
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.