Unique Joint And Neuromuscular Characteristics Dictate Loss Of Stretch-Shortening Cycle Potentiation In Older Adults

Abstract

<h3>Research Objectives</h3> To compare the rate of force development (RFD) and the stretch-shortening cycle (SSC) potentiation of eccentric-preloaded concentric contraction between young and older populations at 3 different velocities: 120°/s, 180°/s, and 240°/s for 3 different range of motions (ROMs): small (ROM for walking), medium, and large (ROM for balance recovery from moderate to severe large-intensity perturbations, respectively) at the ankle. <h3>Design</h3> Cross-sectional study. <h3>Setting</h3> University laboratory. <h3>Participants</h3> 23 participants (12 young adults and 11 older adults). <h3>Interventions</h3> Not applicable. <h3>Main Outcome Measures</h3> Ankle plantarflexors were measured randomly for concentric only and eccentric-preloaded concentric muscle strength at 3 different velocities (120°/s, 180°/s, and 240°/s) at 3 different ROMs (small, medium, and large) on an isokinetic device. Body-mass normalized differences between eccentric-preloaded concentric torque and concentric torque without any preloading was calculated as SSCpotentiation. Average RFD (slope of eccentric-preloaded maximum concentric torque-time curve) was calculated for all the conditions in young and older adults. <h3>Results</h3> SSCpotentiation at the ankle in older adults was lower than young adults at 120°/s for the middle ROM (p ≤ 0.05, d = 0.3), and at 240°/s for the large ROM (p = 0.035, d = 0.3). Older adults had significantly lower RFD of eccentric-preloaded concentric torque at the ankle at 120°/s and 240°/s (p ≤ 0.05, d = 0.8 - 1.8) for the middle ROM, and at 120°/s, and 180°/s for the large ROM (p < 0.05, d = 1.0 - 2.6) than young. <h3>Conclusions</h3> SSCpotentiation and RFD of eccentric-preloaded concentric torque at the ankle are lower in older adults than young adults. The degree of deficit of RFD is markedly higher than SSCpotentiation in older adults. Whether these deficits with aging explain a greater risk of mobility-loss and falls remains unknown. <h3>Author(s) Disclosures</h3> No conflict of interest.