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.