Fatigue of abdominal and paraspinal muscles during sustained loading of the trunk in the coronal plane

OBJECTIVE: To measure fatigue-related changes in the electromyographic signals of trunk muscles during lateral bend loading, and to determine the effects of load magnitude, gender, and contraction time on these changes. DESIGN: A factorial experimental design. SETTING: A research laboratory. PARTICIPANTS: Twenty-four healthy volunteers (12 men, 12 women; mean age +/- SD, 22.9 +/- 3.1 yrs). INTERVENTION: Subjects sustained lateral bend loads at 20%, 40%, and 60% of their maximal exertion. OUTCOME MEASURES: Median frequency and total power of the power spectrum of the electromyographic signals. RESULTS: Trunk muscles' median frequency signals decreased and their total power increased as contraction time increased. These changes became more pronounced as the magnitude of loading increased. Men and women showed a similar rate of median frequency decline, but the total power of signals in men was larger than that in women. All muscles showed signs of fatigue, except that at 20% of maximal exertion only thoracic erector spinae fatigued significantly. CONCLUSIONS: Endurance training of paraspinal and abdominal muscles may be useful in preventing low back pain associated with lateral bend loading. The risk of back pain is similar in both genders and is higher with larger load magnitude and longer contraction time.