Arnold Schwarzenegger, who had arguably the best biceps peak in the history of bodybuilding, would frequently comment on how important it was to squeeze at the top to get a peak (concentric) contraction when training biceps. Squeezing the muscle concentrically is key to stimulating growth.
PROSECUTION
Compared with concentric contractions, eccentric contractions are potentially more effective because more weight can be lowered eccentrically than can be lifted concentrically.
EVIDENCE
During an eccentric contraction, fewer fibers are actively contracting, placing higher force demands per fiber than during concentric contractions.
Eccentric contractions produce more muscle damage than concentric contractions.
A recent meta-analysis reviewing the results of 15 independent studies revealed that although concentric contractions are able to elicit gains in muscle mass comparable to eccentric contractions, on average eccentric contractions are more effective for mass gains.
VERDICT
On average, eccentric training produces greater gains in muscle mass compared with concentric training (10% versus 6.8%, respectively).
SENTENCING
It must be acknowledged that one of the primary reasons eccentric work is more effective than concentric work is that greater loads can be used eccentrically, producing a more potent growth stimulus. With greater weight loads come greater potential risk of injury. That being said, emphasis should always be placed on good eccentric contractions during any exercise that is being performed. Any additional eccentric-specific work should be done prudently, with appropriate spotters and with a volume of work that is still within your ability to recover between training sessions.
