Intermittent stretch reduces force and central drive more than continuous Stretch
Lippincott Williams and Wilkins
Faculty of Health, Engineering and Science
Centre for Exercise and Sports Science Research
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 (Tpeak), voluntary activation (%VA; interpolated twitch technique), EMG amplitude normalized by Mmax (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 Tpeak 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 Tpeak 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 Tpeak more than CS, and these reductions were strongly associated with a depression in central drive.