Muscle activation during exercises to improve trunk stability in men with low back pain.
OBJECTIVE
To evaluate the relative activation amplitudes from 3 abdominal and 2 trunk extensor muscle sites of persons with low back pain (LBP) performing the pelvic-tilt, the abdominal-hollowing, and level 1 of the trunk stability test (TST) exercises and to compare the activation amplitudes among muscle sites and exercises.


METHODS
A prospective, comparative, repeated-measures design.


METHODS
Motion analysis research laboratory.


METHODS
Fourteen men with LBP (mean duration, 8y; mean age +/- standard deviation, 39+/-5y).


METHODS
Subjects performed 3 exercises in random order while surface electromyograms were recorded from 5 muscle sites: lower and upper rectus abdominus, external oblique, erector spinae, and multifidus. The exercises were divided into 2 phases: a movement phase and a stabilization phase. The root-mean-square (RMS) electromyographic amplitude for each phase was calculated and normalized to the highest RMS amplitude from a series of 4 exercises, which attempted to elicit maximal voluntary isometric contractions (MVICs) for each muscle. A 2-factor, repeated-measures analysis of variance (ANOVA) tested the muscle by exercise interaction and the 2 main effects for each phase separately.


METHODS
Normalized RMS amplitude was the main dependent variable. The ensemble-average profiles for each muscle were calculated to examine the phasing of activation throughout the exercises.


RESULTS
The ANOVA revealed a statistically significant muscle-by-exercise interaction (P<.05) for both phases, which showed that the 3 exercises; recruited the 5 muscle sites using different patterns of relative amplitudes. The external oblique muscle site was activated to higher amplitudes than the other 4 muscle sites for all 3 exercises; the highest normalized RMS activity occurred at the external oblique during the pelvic tilt (32% MVIC). The phasic patterns among the 5 muscle sites were not consistent for the TST but were consistent among the 5 sites for the other 2 exercises.


CONCLUSIONS
None of the exercises recruited the abdominal muscles to intensities deemed adequate for strengthening. The TST challenges the coordination of muscle activity during the leg-loading task (stabilization phase) as evidenced by changes in amplitudes over the total exercise time for the external oblique site, but not the other 4 sites. All 3 exercises could be used as initial exercises in a dynamic stability progression when low-recruitment amplitudes of specific muscles were the objective but not for strengthening.
Hubley-Kozey
Cheryl L
CL
School of Physiotherapy, Dalhousie University, Halifax, NS, Canada. clk@is.dal.ca
Vezina
M Johanne
MJ
D000009:Abdominal Muscles / Q000503:physiopathology*; D000328:Adult; D000704:Analysis of Variance; D002908:Chronic Disease; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D005081:Exercise Therapy; D006801:Humans; D017116:Low Back Pain / Q000503:physiopathology / Q000534:rehabilitation*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D011446:Prospective Studies; D011999:Recruitment, Neurophysiological