The Acute Effects of Static Stretching on Human Hopping Performance

Abstract

Static stretching is related to increases in joint range of motion (ROM), however, the relationship between stretching and movement performance is unclear. Some suggest an acute bout of stretching enhances neuromuscular performance, whereas other evidence points to a detrimental effect. PURPOSE: To determine the acute effects of static stretching on performance measurements of a bouncing gait represented by bipedal hopping. METHODS: Participants were randomly assigned to either a control (C) or static stretching (EXP) group (n=12 each group). Plantar-flexor muscle activity, active ankle joint stiffness (kA), and leg stiffness (kL) were measured during preferred-height hopping. These variables were calculated for the lowering phase of ground contact, from initial contact to the lowest vertical position of the center of mass (COM). Muscle activity was measured with surface electromyographic (EMG) electrodes over the gastrocnemius (lateral and medial) and soleus muscles. Active kA was calculated as the ratio of net muscle torque to ankle angular displacement and kL was calculated as the ratio of change in vertical GRF to vertical displacement of the COM. Hopping frequency was maintained at 2.2 Hz with the aid of a metronome. In addition, measurements of active ankle dorsiflexion ROM were recorded before each trial of hopping. Participants performed two trials of 60-s hopping. Between trials the EXP group participated in static stretching of the plantar-flexor muscles and C group rested. Comparison of the change in hopping variables from one trial to the next was made between groups using a one-way MANO VA and comparison of change in active ROM between groups was made with a one-way ANOVA. RESULTS: Univariate examination of changes in active dorsiflexion ROM between the C and EXP groups demonstrated a difference (AROM: 0.0(1.1) vs. 1.6(2.0) degrees, p=0.02). Multivariate examination of the changes in hopping variables from one trial to the next showed no difference between groups (muscle activity ratio: 0.9(0.2) vs. 1.0(0.2) IEMG post/pre, δkA: 8(50) vs. 20(32) Nm rad−1, δkL 0.3(1.9) vs. 0.1(1.2) kN m−1, p=0.46). All data are presented as mean (SD), C and EXP respectively. CONCLUSIONS: The observed increase in ankle dorsiflexion ROM after static stretching is in agreement with previous findings. There is, however, no support for either an enhancing or detrimental effect of static stretching on performance measures during bipedal hopping.