Acute Effects of Static Stretching on Leg Extension and Flexion Isokinetic Peak Torque and the Hamstring-to- Quadriceps Ratio

Abstract

INTRODUCTION: Low hamstring-to-quadriceps isokinetic peak torque ratios have been associated with an increased risk of injury. Since stretching may decrease isokinetic peak torque, it is possible that hamstring stretching may adversely affect the hamstrings:quadriceps (H:Q) ratio. PURPOSE: To examine the acute effects of traditional hamstring and calf static stretching on leg flexion and leg extension isokinetic peak torque (PT) and the H:Q ratios at 60, 180, and 300° s−1. METHODS: Six men (mean ± SD age = 24.0 ± 6.3 yrs; body mass = 89.3 ± 13.1 kg; height = 177.1 ± 6.6 cm) and six women (21.7 ± 1.2 yrs; 62.2 ± 5.9 kg; 165.9 ± 6.2 cm) performed three maximal voluntary unilateral isokinetic leg extension and flexion muscle actions at three randomly ordered angular velocities (60, 180, and 300°·s−1) before and after a bout of hamstring and calf static stretching. The stretching protocol consisted of 1 unassisted and 3 assisted static stretching exercises designed to stretch the posterior muscles of the thigh and leg. Four repetitions of each stretch were held for 30 s with 20-s rest between repetitions. Three separate three-way mixed factorial ANOVAs (time x velocity x gender) were used to analyze the leg extension and flexion PT as well as the H:Q ratio data. RESULTS: There were no interactions (p > 0.05) for leg extension PT or H:Q ratio, however, the main effects for velocity (p ≤ 0.05) indicated that PT decreased and H:Q ratio increased from 60 to 300°·s−1. There was a three-way interaction (time x velocity x gender; p ≤ 0.05) for leg flexion PT. Post-hoc t-tests indicated that leg flexion PT decreased (p ≤ 0.05; 11.5%) from pre- to post-stretching at 60°·s−1 for the women. However, no other stretching-related changes were observed. CONCLUSIONS: Our findings indicated that there were velocity-specific, stretchinginduced decreases in leg flexor isokinetic PT at 60°·s−1, but not 180 and 300°·s−1, for the women, but not the men. However, this decrease was not sufficient to alter the H:Q ratio. In addition, the stretching did not affect leg extension (antagonist) strength. These findings suggested that static stretching of the hamstrings and calf muscles may not adversely affect the H:Q ratio, despite transient decreases in leg flexor strength at 60°·s−1 in women.