The Use of Magnetic Resonance Imaging to Evaluate Lumbar Muscle Activity During Trunk Extension Exercise at Varying Intensities

Abstract

Descriptive, repeated measures analysis of exercise-induced changes in lumbar muscle transverse relaxation time (T2). To use muscle functional magnetic resonance imaging (MRI) to characterize the activity levels and recruitment patterns of the lumbar extensor muscles during trunk extension exercise over 3 intensities. Contrast shifts in T2 are indicative of skeletal muscle activity during resistance exercise and are used to characterize the function of a variety of muscles. The use of muscle functional MRI for the lumbar muscles has been limited. In 11 healthy participants, T2 was calculated for the lumbar quadratus lumborum, iliocostalis lumborum, longissimus thoracis, and multifidus at rest and following dynamic trunk extension exercise at 3 exercise intensities (40%, 50%, and 70% peak intensity). The multifidus displayed the largest T2 increase at each of the 3 exercise intensities, followed by the erector spinae and, finally, the quadratus lumborum. At the lowest intensity, the medial erector spinae (longissimus thoracis) displayed a higher T2 increase than the lateral group (iliocostalis lumborum), while at the higher intensities, this pattern was reversed. In general, the T2 increase was higher during exercise at 50% and 70% intensities than at 40%, while there was no difference in T2 increase between 50% and 70%. Muscle functional MRI can be used to characterize lumbar muscle function during trunk extension exercise. The levels and recruitment patterns of the lumbar extensors, as measured by muscle T2 shifts, vary with exercise intensity. Future research is needed to assess the mechanism of the nonlinear relationship between T2 shifts and exercise intensity, and to clarify the effects of fatigue and the order of exercise presentation on the T2 response of the lumbar extensors.