Effect of maturation on the relationship between muscle size and force production

Although it is well accepted that an increase in muscle size is linked to an increase in muscle force, the relationship between muscle size and maximal strength during maturation is still discussed. In the present study we aimed at determining whether maturation affects the relationship between muscle size and maximal strength, and we investigated the reasons accounting for the discrepancies among previous studies.

Maximal isometric handgrip force (Fmax) and forearm muscle size were measured in 14 prepubertal boys (11.3 +/- 0.8 yr old), 16 adolescents (13.3 +/- 1.4 yr old), and 16 men (35.4 +/- 6.4 yr old). Anatomic maximal cross-sectional area (MCSA) and muscle volume (VM) were measured using MRI, and these results were compared with muscle volume (VL) obtained from anthropometric measurements.

Fmax was linearly correlated with VM (r2 = 0.90), VL (r2 = 0.85), and MCSA (r2 = 0.87), while VM was strongly correlated with VL (r2 = 0.90). The Fmax/VM ratio did not differ among groups, whereas Fmax/VL and Fmax/MCSA ratios were significantly higher in adults than in children and adolescents. These results demonstrated that, when compared with MRI, anthropometric measurements led to a systematic overestimation of muscle volume. In addition, this overestimation was significantly larger in children (43.1%) and adolescents (38.5%) as compared with adults (20.5%) (P < 0.05).

Our results showed that the maximal isometric strength exerted by the forearm muscles in humans is proportional to their size whatever the age, and that VM is the best index of muscle size during growth. The previously reported increased ability to produce maximal strength from childhood to adulthood could be explained by systematic bias introduced by the method used to characterize muscle size instead of physiological or neural changes.