One minute plantar flexors’ static stretch transiently increases H-reflex excitability and exerts no effect on corticospinal pathways

Abstract

The purpose of this study was to determine whether the neural responses observed following static stretching are mediated by muscle spindles sensitivity, spinal excitability or cortical excitability and how long these influences last. Nineteen volunteers (25.7 ± 5.6 years) were tested for tap reflex (T-reflex), H-reflex and motor evoked potentials (MEPs) on ankle flexors and extensors at immediately, five and ten minutes after one minute static stretching applied at individual maximal ankle dorsiflexion, as well as immediately, five and ten minutes after a control period of same duration. Comparison of measurements collected immediately after conditions (post_00) revealed that T-reflex was weaker following stretching compared to control (−59.2% P = .000). T-reflex showed a slow recovery rate within the first 150 seconds after stretching, however five minutes after (post_05) the inhibition has disappeared. H-reflex increased immediately after stretching (+18.3%, P = .036), showed a quick tendency to recover and returned to control values within five minutes from stretching. MEPs were not affected by the procedure. These results suggest that one minute static stretching decreases primarily muscle spindle sensitivity and facilitate H-reflex whilst effects on motor cortex can be excluded.

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