The rate of velocity development associates with muscle echo intensity, but not muscle cross-sectional area in older men

The examination of mechanisms contributing to the age-related reductions in rapid velocity development is limited. The purpose of this study was to examine the influence of muscle cross-sectional area (CSA) and echo intensity (EI) on plantarflexor rate of velocity development (RVD) in older adults. Twenty-two men (mean ± SD age = 69 ± 3 years) performed three maximal plantarflexion voluntary isokinetic muscle actions at a velocity of 2.09 rad · s^-1. Peak RVD was determined as the peak derivative of the velocity-time curve from the onset of velocity development to the onset of the load range. B-mode ultrasound was used to examine CSA and EI from the lateral and medial gastrocnemius. Plantarflexor RVD was related to EI (r = -0.491, P = 0.020), but not CSA (r = -0.003, P = 0.989). The findings of the present investigation suggest that alterations in muscle tissue composition (i.e., increase in intramuscular fat and/or fibrous tissue) may influence the ability of older adults to rapidly accelerate their limb.