Intermittent Stretch Reduces Force and Central Drive more than Continuous Stretch

Introduction The relative contributions of central versus peripheral factors to the force loss induced by acute continuous and intermittent plantarflexor stretches were studied. Methods Eighteen healthy young men with no apparent tissue stiffness limitations randomly performed 1) one 5-min stretch (continuous stretch [CS]), 2) five 1-min stretches (intermittent stretch [IS]), and 3) a control condition, on three separate days. The stretches were constant-torque ankle stretches performed on an isokinetic dynamometer. Gastrocnemius medialis oxygenation status was quantified during stretch using near-infrared spectroscopy. Measures of isometric plantarflexor peak torque (T-peak), voluntary activation (%VA; interpolated twitch technique), EMG amplitude normalized by M-max (EMG:M), V-wave amplitude, and excitation-contraction (E-C) coupling efficiency (torque ratio between 20- and 80-Hz tetanic stimulations [20:80]) were taken before, immediately, and 15 and 30 min after each condition. Results IS caused substantial cyclic variations in tissue oxygenation, but CS resulted in a greater decrease in oxyhemoglobin concentration. Voluntary T-peak decreased more after IS (-23.8%) than CS (-14.3%) and remained significantly depressed until 30 min after IS only (-5.6%). EMG:M (-27.7%) and %VA (-15.9%) were reduced only after IS. After CS and IS, the magnitude of decrease in T-peak was correlated with decreases in EMG:M (r = 0.81 and 0.89, respectively), %VA (r = 0.78 and 0.93), and V-wave (r = 0.51, only after IS). Tetanic torque values (20 and 80 Hz) were decreased after IS (-13.1% and -6.4%, respectively) and CS (-10.9% and -6.7%, respectively), but 20:80 was not different from the control group. Conclusion These results suggest that IS reduced T-peak more than CS, and these reductions were strongly associated with a depression in central drive.