A comparison of trunk muscle activation amplitudes during gait in older adults with and without chronic low back pain.

Objective: To investigate abdominal and low back muscle activation amplitudes of older adults (at least 50 years of age) experiencing nonspecific chronic low back pain (LBP) and of adults without LBP while they walked on a level surface at a self-selected speed.

Design: Cross-sectional.

Setting: Dynamics of human motion laboratory.

Participants: Nine asymptomatic control participants (mean ± standard deviation: 64.9 ± 8.8 years) and 9 participants experiencing LBP (61.4 ± 9.8 years) were selected for this study.

Methods: Surface electromyography (EMG) was recorded over the bilateral lower rectus abdomini, internal obliques, lateral erector spinae longissimus, and lumbar multifidus muscle sites while participants walked across a pressure-sensor mat at a self-selected speed. To normalize EMG amplitudes during gait, the participants performed a series of maximal voluntary isometric contractions. EMG signals were full-wave rectified and low-pass filtered to yield a linear envelop waveform. For the gait trials, a window was identified from right heel strike to the second left heel strike and 4 subphases, including right and left loading response and mid stance, were identified. EMG amplitudes were calculated for each subphase.

Main Outcome Measurements: Two sample t-tests compared demographic information and spatiotemporal gait parameters between groups. EMG activation amplitude differences between groups and among subphases of gait were analyzed for each muscle with use of general linear models, followed by Tukey honestly significant difference post hoc comparisons.

Results: No differences were found between the groups for demographic or gait parameters. The control group participants activated their lower rectus abdomini muscles (P < .05) and right internal oblique muscles significantly more than did the LBP group (P < .05), whereas the LBP group activated their left lateral erector spinae and both lumbar multifidi sites significantly more than did the control group (P < .05).

Conclusions: The activation amplitudes of the anterior muscle sites were lower for participants with LBP, whereas the posterior sites were activated to higher amplitudes than in the control group. Although most muscles responded to the subphases indicating muscle synergies, the group by muscle interactions for the right internal oblique and lateral erector spinae show that the differences between groups were not systematic. These results describe neuromuscular alterations in persons between 50-80 years with LBP that can be used for developing subject-specific management related to maintaining spinal stability.