The Influence Of A 20-Minute Jog On The Viscoelastic Properties Of The Plantar Flexor Muscles

Abstract

INTRODUCTION: It is commonly believed that passive stretching is most appropriate when performed following a workout. However, the viscoelastic response during passive stretching prior to and following a common cardiovascular workout is unclear. PURPOSE: To examine the influence of a 20-min, moderate-intensity jog on the viscoelastic properties of the plantar flexor muscles. METHODS: Six recreationally active males (mean age ± SD = 23 ± 3 yrs; stature = 172 ± 4 cm; mass = 75 ± 7 kg) participated in two randomized experimental trials separated by 2-7 days; 1) a 20-min jog (mean % age-predicted HRmax ± SD = 83 ± 4) on a Quinton Club Track treadmill or 2) 20-min rest. Each condition was immediately followed by six 30-s stretches on a calibrated Biodex System 4 dynamometer. The dynamometer slowly (5°·sec-1) stretched the plantar flexors to a constant torque (i.e. 27 Nm) value (point of discomfort). Once this threshold was reached, the dynamometer was stopped and held at the same position for the entire 30-s. During the six 30-s stretches, torque values were recorded every 5-s (0, 5, 10, 15, 20, 25, and 30) to assess viscoelastic stress relaxation and position was recorded at the onset of each stretch to measure viscoelastic creep. Two-way repeated measures analysis of variance (ANOVA) was used to analyze changes in joint angle and a three-way repeated measures ANOVA was used to analyze changes in torque during the six 30-s stretches. An alpha of P≤0.05 was used to determine statistical significance. RESULTS: For stress relaxation, there was a significant interaction for stretch x time (P = 0.001). Torque declined in a similar fashion for all stretches over the 30-s stretch period and began to plateau around 25-s. For creep, there was a significant main effect for stretch (P = 0.001). The joint angle for stretch 6 was greater than stretches 1-4, stretches 3-5 were greater than stretches 1-2, and stretch 2 was greater than stretch 1. CONCLUSIONS: The viscoelastic responses (stress relaxation and creep) were similar for both conditions. These findings suggest that a 20-min, moderate-intensity jog had little influence on the viscoelastic responses seen during a practical stretching protocol.