Eccentric exercise-induced muscle weakness amplifies the history dependence of force

Introduction Following active lengthening or shortening contractions, isometric steady-state torque is increased (residual force enhancement; rFE) or decreased (residual force depression; rFD), respectively, compared to fixed-end isometric contractions at the same muscle length and level of activation. Though the mechanisms underlying this history dependence of force have been investigated extensively, little is known about the influence of exercise-induced muscle weakness on rFE and rFD. Purpose Assess rFE and rFD in the dorsiflexors at 20%, 60%, and 100% maximal voluntary torque (MVC) and activation matching, and electrically stimulated at 20% MVC, prior to, 1 h following, and 24 h following 150 maximal eccentric dorsiflexion contractions. Methods Twenty-six participants (13 male, 24.7 +/- 2.0y; 13 female, 22.5 +/- 3.6y) were seated in a dynamometer with their right hip and knee angle set to 110 degrees and 140 degrees, respectively, with an ankle excursion set between 0 degrees and 40 degrees plantar flexion (PF). MVC torque, peak twitch torque, and prolonged low frequency force depression were used to assess eccentric exercise-induced neuromuscular impairments. History-dependent contractions consisted of a 1 s isometric (40 degrees PF or 0 degrees PF) phase, a 1 s shortening or lengthening phase (40 degrees/s), and an 8 s isometric (0 degrees PF or 40 degrees PF) phase. Results Following eccentric exercise; MVC torque was decreased, prolonged low frequency force depression was present, and both rFE and rFD increased for all maximal and submaximal conditions. Conclusions The history dependence of force during voluntary torque and activation matching, and electrically stimulated contractions is amplified following eccentric exercise. It appears that a weakened neuromuscular system amplifies the magnitude of the history-dependence of force.