Chronic stretching and voluntary muscle force.

The purpose of the study was to determine whether muscle force, power, and optimal length were affected by 4 weeks of static or ballistic stretching. Twenty-nine males (age, 18-60 years) performed 4 maximal hip extensions to measure peak torque (PT), rate of torque development (RTD), work (W), and PT angle (PTA). Then, participants completed 4 weeks of static or ballistic flexibility training of the hip extensors followed by repetition of the testing protocol. After training, PT increased 5.3 +/- 19.0% in the static group (SG), 7.8 +/- 12.7% in the ballistic group (BG), and 6.1 +/- 17.9% in the control group (CG). RTD increased 4.8 +/- 22.7% in the SG, 3.6 +/- 28.0% in the BG and 9.7 +/- 24.0% in the CG. W increased 3.9 +/- 7.0% in the SG, 14.7 +/- 27.4% in the BG, and 5.5 +/- 9.5% in the CG. PTA changed little with a -1.6 +/- 6.6% decrease in the SG and increases of 0.86 +/- 4.1% in the BG and 0.18 +/- 8.7% in the CG. None of the results were statistically different between stretching group and CG (alpha = 0.05). These data suggest that 4 weeks of stretching have little effect on muscle strength, power, W, or length-tension relationship. PTA changed little, suggesting that a lengthening of the muscle with stretching did not occur. It is suggested that individuals can routinely stretch following exercise to maintain flexibility but should avoid stretching prior to exercise requiring high levels of muscle force. Before exercise that requires high muscular forces, individuals may perform dynamic, sport-specific exercises to increase blood flow, metabolic activity, temperature, and compliance of the muscle.