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 before 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 history of lower extremity injury.

INTERVENTION

Subjects performed one hamstring stretch and four calf stretches for 90 seconds, bicycled for 30 minutes as a warm-up, and stretched again.

MAIN OUTCOME MEASURE

EMG was recorded at time 0, 30, 60, and 90 seconds during the stretches before and after warm-up. Recorded values were normalized to EMG during maximum manual muscle testing (MMT). A two-way analysis of variance with repeated measures (p < 0.05) was done to compare EMG activity during stretching before and after warm-up as well as over time.

RESULTS

Low EMG activity was seen for all muscles (< 20% MMT). It was constant over the time of the stretch for all muscles, but it increased in the soleus during the bent knee stretch position. There was a statistically significant decrease in the EMG activity after the warm-up for the gastrocnemius using the traditional and heel off stretching positions and for the soleus 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 EMG 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 differences before and after warm-up.