INTRODUCTION: Loss of lumbar extensor muscle strength and fatigue resistance may contribute to functional disability. METHODS: Two groups of subjects were recruited: young (n = 26, 20-35 years of age) and old (n = 26, >/=65 years of age) adults. Lumbar extensor muscle strength was measured with a load cell, and electromyographic activities were recorded to study muscle fatigue at 60% of maximum voluntary contraction. RESULTS: We found that the muscle moments generated by the extensor muscles decreased with age (P < 0.05). Aging was associated with a significant increase in the power of the lower frequency band (101-200 Hz) of the electromyographic signals (P < 0.05), but the spectral characteristics did not appear to change with sustained contraction (P > 0.05). CONCLUSIONS: The changes in strength and spectral properties of the electromyographic signals of lumbar extensor muscles may be related to age-related alterations in muscle fiber composition and recruitment. These changes should be considered in clinical functional task evaluation.
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