How Back-Muscle Fatigue Influences Lumbar Curvature

CONTEXT: Back-muscle fatigue and lumbar curvature are related to low back pain, but the relation between them is unknown. OBJECTIVE: To clarify whether lumbar curvature changes with back-muscle fatigue. DESIGN: Prospective pseudorandomized. SETTING: Laboratory. PARTICIPANTS: 13 healthy men without low back pain. INTERVENTION: To induce back-muscle fatigue, subjects performed a repetitive prone back-extension exercise from 45 degrees to 0 degrees until exhaustion and then rested 10 min. They performed this exercise 3 times. MAIN OUTCOME MEASURES: Before the trial and after each exercise, lumbar curvature was measured with a Spinal Mouse. RESULTS: After back-muscle fatigue, lumbar curvature decreased significantly (P < .01). This decrease occurred at L4-S1, which was defined as the lower spine. On the contrary, curvature of the upper lumbar spine, at Th12-L4, did not decrease. CONCLUSION: Lumbar curvature, especially the lower portion, decreased with back-muscle fatigue induced by prone back-extension exercise.