Submitted on June 29, 2007
Accepted on December 10, 2007
Gastrocnemius muscle specific force in boys and men
Christopher I. Morse1, Keith Tolfrey1, Jeanette M. Thom2, Vasilios Vassilopoulos3, Constantinos Nicolaos Maganaris1, and Marco Vincenzo Narici1*
1 Department of Exercise and Sport Science, Manchester Metropolitan University, Alsager, United Kingdom
2 School of Sport, Health and Exercise Sciences, University of Wales Bangor, United Kingdom
3 Department of Exercise and Sport Science, Manchester Metropolitan University, Cheshire, Alsager, United Kingdom
* To whom correspondence should be addressed. E-mail: m.narici{at}mmu.ac.uk.
The aim of this study was to assess whether the in vivo specific force and architectural characteristics of the lateral gastrocnemius (GL) muscle of early pubescent boys (n=11, age= 10.9 ± 0.3 years, Tanner stage 2) differed from those of adult men (n=12, age= 25.3 ± 4.4 years). Plantarflexor torque was 55% lower in the boys (77.4 ± 21.4 Nm) compared to the adults (175.6 ± 31.7 Nm, P < 0.01). Physiological cross sectional area (PCSA), determined in vivo using ultrasonography and MRI, was 52% smaller in the boys (P < 0.01). No difference was found in pennation angle; or the ratio of fascicle length (Lf) to muscle length between the boys and men. Moment arm length was 25% smaller in the boys (P < 0.01). Antagonist coactivation assessed using surface EMG on the dorsiflexors was not different between the boys and men (11.8 ± 6.7% and 13.5 ± 5.8%, respectively). After accounting for differences in moment arm length, co-activation, and muscle architecture, GL force normalized to PCSA (specific force) was significantly higher (21%) in the boys than in the men (13.1 ± 2.0 N·cm-2vs. 15.9 ± 2.7 N·cm-2, P < 0.05). In conclusion, the specific force of the plantarflexor muscles of early-pubertal boys appears to be higher than that of young male adults. This finding could not be explained by differences in moment arm length, muscle activation, or architecture and other factors, such as tendinous characteristics and/or changes in moment arm length with contraction, may be held responsible.
