The relative contributions of central versus peripheral factors to the force loss induced by acute continuous and intermittent plantarflexor stretches were studied.
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.
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.
These results suggest that IS reduced Tpeak more than CS, and these reductions were strongly associated with a depression in central drive.
Centre for Exercise and Sports Science Research, School of Exercise and Health Sciences, Edith Cowan University, AUSTRALIA
Address for correspondence: Gabriel S. Trajano, Centre for Exercise and Sports Science Research, School of Exercise and Health Sciences, Edith Cowan University, 270 Joondalup Drive, Joondalup, WA 6027, Australia; E-mail: email@example.com.
Submitted for publication July 2013.
Accepted for publication October 2013.