Independent activation in adjacent lumbar extensor muscle compartments

The purpose of this study was to examine compartmentalization in human lumbar spine extensors. Structure and innervation of these muscles would suggest the possibility of more segmentally specific biomechanical functions than have been found in previous studies examining muscle activation patterns during simple spine bending and twisting tasks. We selected specialized tasks to more effectively investigate the degree of independent control possible within lumbar spine extensors. We recorded surface electromyograms (SEMG) from the right posterior lumbar region during performance of two segmentally specific bellydance skills by seven novice and five trained subjects. These movements were performed at two frequencies (0.5 and 1 Hz). Cross-correlations were performed between pairs of rectified, low-pass filtered (6 Hz) SEMG signals to determine temporal lags between rhythmic bursts. Results showed a difference in the timing of muscle activation above and below the third lumbar vertebra. Temporal asynchrony was independent of either skill level or tempo, suggesting a hard-wired capacity for independent control of adjacent muscle compartments. The results have implications for understanding trunk control in the context of postural stability and postural adaptation during locomotion, as well as for lower back functional assessment and rehabilitation.