Biomechanical and skeletal muscle determinants of maximum running speed with aging.

Purpose: Aging diminishes the ability to run fast, but the specific mechanisms responsible for this deterioration remain largely unknown. In the present study, we investigated the age-related decline in sprint running ability through a cross-sectional examination of biomechanical and skeletal muscle characteristics in 77 competitive male sprinters aged 17-82 yr.
Methods: Ground reaction force (GRF) and kinematic stride cycle parameters were measured during the maximum-velocity phase using a 9.4-m-long force platform. Knee extensor (KE) and ankle plantar flexor (PF) structural characteristics were investigated using ultrasonography and muscle biopsies (vastus lateralis). Force production characteristics of leg extensor muscles were determined by dynamic and isometric contractions.
Results: The main findings were as follows: 1) the progressive age-related decline in maximum running velocity (Vmax) was mainly related to a reduction in stride length (Lstr) and an increase in ground contact time (tc), whereas stride frequency showed a minor decline and swing time remained unaffected; 2) the magnitude of average braking and push-off resultant GRFs declined with age and associated with Lstr, tc, and Vmax; 3) there was an age-related decline in muscle thickness, Type II fiber area and maximal and rapid force-generating capacity of the lower limb muscles; and 4) muscle thickness (KE + PF) was a significant predictor of braking GRF, whereas the countermovement jump height explained most of the variance in push-off GRF in stepwise regression analysis.
Conclusions: Age-related slowing of maximum running speed was characterized by a decline in stride length and an increase in contact time along with a lower magnitude of GRFs. The sprint-trained athletes demonstrated an age-related selective muscular atrophy and reduced force capacity that contributed to the deterioration in sprint running ability with age.