Doing exercises where you push the weight up (concentric) makes more muscle repair cells grow than doing exercises where you lower the weight slowly (eccentric), at least in young men training for 12 weeks.
Scientific Claim
Concentric resistance training is associated with greater increases in satellite cell content in both type I and type II muscle fibers compared to eccentric resistance training in young men after 12 weeks of unilateral knee extension training, suggesting contraction mode differentially influences muscle stem cell activation during hypertrophy.
Original Statement
“Conc training elicited increases in type I fiber SCs of 132 ± 21% and 78 ± 30% (P < 0.001) in the Whey and Placebo group, respectively. This was greater than with Ecc training (P < 0.05), where tendencies (P = 0.08) toward increases were observed... For SCs associated with type II fibers, Conc training increased the SC content by 78 ± 26% and 81 ± 43% (P < 0.01)... which was greater than Ecc training (P < 0.05), which did not evoke any changes.”
Evidence Quality Assessment
Claim Status
overstated
Study Design Support
Design supports claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The study uses causal language ('constitutes a stronger driver') in the abstract and conclusion, but randomization status is unknown, preventing causal inference. Only associative language is justified.
Evidence from Studies
Supporting (1)
Influence of exercise contraction mode and protein supplementation on human skeletal muscle satellite cell content and muscle fiber growth.
This study found that lifting weights by pushing up (concentric) made more muscle stem cells grow in both slow and fast muscle fibers than lowering weights slowly (eccentric), which means pushing up is better at turning on muscle repair and growth signals.