Electromyographic investigation of stretching: The effect of warm-up

Objective: To compare the fine wire electromyographic (EMG) firing patterns during static stretches in the biceps femoris, soleus, and gastrocnemius b efore and after warm-up as well as over time. Design: Experimental single group pretest-posttest design. Setting: Biomechanics research laboratory. Participants: Sixteen healthy volunteers 23 to 36 years of age with no hist ory of lower extremity injury. Intervention: Subjects performed one hamstring stretch and four calf stretc hes for 90 seconds, bicycled for 30 minutes as a warm-up, and stretched aga in. Main Outcome Measure: EMG was recorded at time 0, 30, 60, and 90 seconds du ring the stretches before and after warmup. Recorded values were normalized to EMG during maximum manual muscle testing (MMT). A two-way analysis of v ariance with repeated measures (p < 0.05) was done to compare EMC activity during stretching before and after warm-up as well as over time. Results: Law EMG activity was seen for all muscles (<20% MMT). It was const ant over the time of the stretch for all muscles, but it increased in the s oleus during the bent knee stretch position. There was a statistically sign ificant decrease in the EMG activity after the warm-up for the gastrocnemiu s using the traditional and heel off stretching positions and for the soleu s using the heel off stretching position (p < 0.05). The biceps femoris EMG activity showed no significant differences before and after warm-up. Conclusions: EMG activity during static stretching was low. Overall, the EM G activity remained constant with time for a given stretch position. EMG of the soleus and gastrocnemius was significantly less after warm-up for some stretches, whereas the EMG activity of biceps femoris showed no difference s before and after warm-up.