One minute static stretch of plantar flexors transiently increases Hreflex excitability and exerts no effect on corticospinal pathways.

Abstract

What is the central question of this study? What mediates neural responses following static stretching, and how long do these influences last? What is the main finding and its importance? This study shows that 1 min of static stretching inhibits the tendon tap reflex and facilitates the Hreflex without influencing motor-evoked potentials. The results indicate that at least two different mechanisms mediate neural responses after static stretching. The purpose of this study was to determine whether the neural responses observed after static stretching are mediated by sensitivity of muscle spindles, spinal excitability or cortical excitability and how long these influences last. Nineteen volunteers (25.7±5.6years old) were tested for the tendon tap reflex (T-reflex), Hreflex and motor-evoked potentials on ankle flexors and extensors immediately, 5 and 10min after 1 min static stretching applied at individual maximal ankle dorsiflexion, as well as immediately, 5 and 10min after a control period of the same duration. Comparison of measurements collected immediately after stretching or control conditions revealed that the T-reflex was weaker after stretching than after control (-59.2% P=0.000). The T-reflex showed a slow recovery rate within the first 150s after stretching, but 5 min after the inhibition had disappeared. The Hreflex increased immediately after stretching (+18.3%, P=0.036), showed a quick tendency to recover and returned to control values within 5min from stretching. Motor-evoked potentials were not affected by the procedure. These results suggest that 1min of static stretching primarily decreases muscle spindle sensitivity and facilitates the Hreflex, whereas effects on the motor cortex can be excluded.