Trunk muscle responses to demands of an exercise progression to improve dynamic spinal stability.

Abstract

To compare relative activation amplitudes among abdominal and trunk extensor muscle sites of healthy people performing a leg-loading exercise protocol aimed at progressively challenging spinal stability. A prospective, comparative, repeated-measures design. Motion analysis research laboratory. Eighteen healthy male and female volunteers (mean age +/- standard deviation, 23.8+/-3.4y). Subjects performed 5 progression levels in random order, while surface electromyograms were recorded from 5 abdominal and 2 back extensor muscle sites. Levels 2 through 5 were of interest because they included a leg-extension phase. The root mean square (RMS) amplitude during the leg-extension phase was calculated and normalized to maximal voluntary isometric contractions (MVICs) for each muscle. A 2-factor repeated-measures analysis of variance tested the muscle-by-level interactions and the 2 main effects for the abdominal and trunk extensor sites separately. Bonferroni adjustments were performed on significant results. Normalized RMS (NRMS) amplitude for each muscle during the leg-extension phase. There were statistically significant muscle-by-level interactions (P<.05) for both abdominal and trunk extensor sites. The relative amplitudes increased for the abdominal muscles and erector spinae muscles among levels, except between levels 3 and 4. Significant differences were found among the abdominal muscle sites for the lower-level exercises (levels 2-4), but not for level 5. The highest NRMS amplitude was at level 5, that is, 40% of MVIC. The patterns of activation amplitudes differed among levels; therefore, this was not a simple progressive loading protocol because muscles responded in a nonuniform manner to the demands associated with the various levels of progression. Based on the results, the protocol met some of the objectives of dynamic stability protocols.