Scaling of muscle power to body size: the effect of stretch-shortening cycle.

The present study investigates the relationship between muscle power recorded in vertical jumps and body size, and explores possible differences in this relationship between the concentric (CON) and stretch-shortening cycle (SSC) muscle action. Physical education students (N = 159) were tested with the performance of various CON and SSC maximum vertical jumps. The relationship between muscle power (P) and body size (S) was assessed by P=aS(b) where a and b were the constant multiplayer and scaling exponent, respectively. With respect to body mass and fat-free mass, the scaling exponents b for mean muscle power (calculated from the ground reaction force) in CON and SSC jumps were within the range 0.69-0.82 and 0.90-1.15, respectively. With respect to body height, the scaling exponent was higher (0.76-0.97 and 1.23-1.79, respectively), but the observed relationship proved to be relatively weak. However, when jump height was used as an index of muscle power, the same exponents were close to zero (suggesting no relationship with any of the indices of body size) in all the jumps except an SSC based hopping jump that demonstrated a weak but positive relation to body size. In conclusion, muscle power could scale to body size at a higher rate than predicted by geometric similarity (i.e. b = 0.67), while larger individuals could gain more when switching from CON to SSC muscle action. These findings could be based on a non-geometric scaling of transversal with respect to longitudinal dimensions and/or on different scaling rates of muscles and tendons.