Influence of muscle hypertrophy on the moment arm of the triceps brachii muscle.

Although the moment arm of the triceps brachii muscle has been shown to be associated with the muscle's anatomical cross-sectional area, whether training-induced muscle hypertrophy alters the moment arm of the muscle remains unexplored. Therefore, the current study aimed to examine this. Eleven men underwent a 12-week resistance training program for the triceps brachii muscle. The maximum muscle anatomical cross-sectional area (ACSAmax), the moment arm of the triceps brachii muscle, and the anterior-posterior dimension of the olecranon were measured using a magnetic resonance imaging system before and after intervention. The ACSAmax (33.6 ± 11.9%, P < .001) and moment arm (5.5 ± 4.0%, P = .001) significantly increased after training, whereas the anterior-posterior dimension of the olecranon did not change (P > .05). The change in moment arm was smaller than that expected from the relationship between the ACSAmax and the moment arm before the intervention. The present results indicate that training-induced triceps brachii muscle hypertrophy could increase the muscle moment arm, but its impact can be small or negligible.