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.