The Claim
In trained individuals, 21 days of daily resistance training at 70% one-repetition maximum results in a mean increase of 0.28 cm in muscle thickness of the elbow flexors, while the contralateral untrained arm shows no significant change, demonstrating that muscle growth requires mechanical overload.
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.
After 21 days of daily weight training at 70% of maximum strength, the muscles in the trained arm grow thicker by 0.28 cm on average, while the untrained arm shows no change, indicating that muscle growth occurs only when muscles are subjected to mechanical stress.
See the scientific wording
In trained individuals, 21 days of daily resistance training with 70% 1RM leads to a mean increase of 0.28 cm in muscle thickness of the elbow flexors, while the untrained arm shows no significant change, indicating that muscle growth requires mechanical overload.
When muscles are stretched and pulled under heavy load, the force damages tiny structures inside muscle cells, which turns on a molecular switch that tells the cell to build more muscle proteins. This causes the muscle fibers to grow thicker over time. Without this heavy pulling, the switch stays off and the muscle does not grow, even if the person gets stronger from better nerve signals.
What the research says
1 studyWhen people lift weights every day for three weeks, their muscles get bigger — but just testing their strength without lifting doesn't make muscles grow. This study proves that actual lifting is needed for muscle growth.
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.