The effect of unilateral muscle pain on recruitment of the lumbar multifidus during automatic contraction. An experimental pain study.

Changes in control of the multifidus muscle are a likely contributor to low back pain (LBP), however, the underlying mechanisms of these changes are not well understood. To date it remains uncertain if pain has a selective effect on the multifidus muscles, in line with the observations of the selective changes in structure in acute LBP, or a more generalized effect. The objective of this study is to help to elucidate whether acute unilateral muscle pain alters the activation of the multifidus specific at the level and side of the pain or has a more widespread effect. An experimental pain protocol using hypertonic saline was applied to induce unilateral low back muscle pain. Automatic activity of the multifidus muscle during arm lifts was evaluated with dynamic ultrasound measurement, by assessing muscle thickness change during contraction. Multifidus activity of 15 healthy subjects was compared in a non-pain and in a pain condition, at different spinal levels (L3-L4-L5) and at both body sides. Unilateral induced pain at one segmental level reduced muscle thickness increase during contraction, at both body sides and at different lumbar levels. These results do suggest that unilateral pain may have a more widespread effect on multifidus muscle recruitment, affecting the left and right muscles, at different lumbar levels.