The influence of a 20-minute jog on the viscoelastic properties of the plantar flexor muscles
American College of Sports Medicine 2011 National Conference
American College of Sports Medicine
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.
Fiddler, R.E., Thompson, B.J., Everett, K.L., Sobolewski, E.J., Smith, D.B., Bond, K.E., Foster, M., Tremble, J., and Ryan, E.D. The influence of a 20-minute jog on the viscoelastic properties of the plantar flexor muscles. Presented at the American College of Sports Medicine national conference, Denver, CO. May 2011. Med Sci Sport Exerc, 43 (5 Suppl.)