Electromyographic investigation of muscle stretching techniques.

Myotatic reflexes can be enhanced following brief static contractions. Since static contractions are often used as precursors to muscle stretch, rationale underlying these techniques were questioned and re-examined through electromyography (EMG). Twenty-one female gymnasts performed three methods to produce hamstring stretch: static (S), contract-relax (CR), and contract-relax with agonist (hip flexors) contraction (CRAC). Hip joint angles and intra-individual electromyograms were statistically compared across stretch conditions. In 12 subjects, the CRAC method elicited significantly greater hamstring EMG activity (P < 0.05) than the other techniques. A higher level of muscle activation was associated with the S method in only one subject. No significant differences in EMG activity across stretch conditions were found in eight subjects suggesting that the relative effectiveness of the stretch techniques varied across individuals. Involuntary paroxysmal tremor activity was occasionally visible in EMG records of most subjects at the low levels of muscle activation. While apparently contributing to increased muscle stiffness, the CRAC technique produced the largest gains in hip flextion. Rank orderings of minimum pain and maximum perceived stretch effectiveness were significantly related with one another, and with decreasing EMG activity, but not with range of motion.