Effect of static stretch on fatigue of lumbar muscles induced by prolonged contraction.

Low back pain (LBP) is believed to be the result of fatigue of the back extensor muscles induced by prolonged contraction. Although static stretch has been considered to promote recovery from such muscle fatigue by relaxation, little is known about the effect of stretch on muscle fatigue, especially in the back extensor muscles. The purpose of this study was to investigate the effect of static stretch on prolonged contraction-inducedfatigue of the back extensor muscles using electromyographic (EMG) spectral analysis in ten healthy volunteers. Bipolar surface electrodes were placed on the longissimus and the multifidus muscles. EMG signals were collected during two trials of a Sorensen trunk-holding test for two minutes, with a five-minute rest period between the two trials (control test). All subjects were asked to perform the same trials, with one-minute of static stretch and a four-minute rest period (stretch test). Maintaining the knees toward the chest in supine position resulted in static stretch. The median frequency (MF) was calculated using a spectrum analysis program, and the MF slope over time was computed by linear regression analysis, and normalized with the y-intercept. The decreasing rate of the normalized MF slope between two trials in two tests was compared. The decreasing rate of the normalized MF slope of the second trial was larger than that of the first trial in the control test (p < 0.05), but no significant difference was observed in the stretch test. The results indicated that static stretch had a significant effect on the recovery from fatigue of the back extensor muscles, since it influenced the decreasing rate of the normalized MF slope.