The effect of lumbar fatigue on the ability to sense a change in lumbar position - A controlled study

Study Design. A cross-sectional study in patients with recurrent/chronic lo w back trouble and healthy control subjects. Objective. To evaluate the effect of paraspinal muscle fatigue on the abili ty to sense a change in lumbar position. Summary of Background Data. Protection against spinal injury requires prope r anticipation of events, appropriate sensation of body position, and reaso nable muscular responses. Lumbar fatigue is known to delay lumbar muscle re sponses to sudden loads. It is not known whether the delay is because of fa ilure in the sensation of position, output of the response, or both. Methods. Altogether, 106 subjects (57 patients with low back trouble [27 me n and 30 women] and 49 healthy control subjects [28 men and 21 women]) part icipated in the study. Their ability to sense a change in lumbar position w hile seated on a special trunk rotation unit was assessed. A motor rotated the seat with an angular velocity of 1 degrees per second. The task in the test involved reacting to the perception of lumbar movement (rotation) by r eleasing a button with a finger movement. The test was performed twice, bef ore and immediately after a fatiguing procedure. During the endurance task, the participants performed upper trunk repetitive extensions against a res istance, with a movement amplitude adjusted between 25 degrees flexion and 5 degrees extension, until exhaustion. Results. Patients with chronic low back trouble had significantly poorer ab ility than control subjects on the average to sense a change in lumbar posi tion (P = 0.007), which was noticed before and after the fatiguing procedur e. Lumbar fatigue induced significant impairment in the sensation of positi on change (P < 0.000001). Conclusions. Lumbar fatigue impairs the ability to sense a change in lumbar position. This feature was found in patients and control subjects, but pat ients with low back trouble had poorer ability to sense a change in lumbar position than control subjects even when they were not fatigued. There seem s to be a period after a fatiguing task during which the available informat ion on lumbar position and its changes is inaccurate.