Differences in Abdominal Muscle Activation Patterns of Younger and Older Adults Performing an Asymmetric Leg-Loading Task

Abstract

Objectives: To determine whether differences exist between younger (20-50 years) and older adults ( 65 years) in abdominal muscle amplitudes, temporal patterns, and threedimensional (3D) pelvic motion, while performing an asymmetric leg-loading task. Design: Cross-sectional. Setting: Neuromuscular function laboratory. Participants: Ten healthy younger (33.3 7.7 years) and 10 healthy gender- and body mass index–matched older adults (69.0 6.6 years). Intervention: Surface electromyograms from 6 abdominal muscle sites bilaterally and pelvic motions were simultaneously recorded. Main Outcome Measure(s): Root mean square (RMS) amplitude during the leg extension phase was calculated for each muscle. Ensemble average waveforms for the total exercise were analyzed using principal component (PC) analysis. Total angular displacement of the pelvis was calculated. Student t tests were performed on demographic and angular displacement data. Three-factor mixed model analysis of variances (group, muscle, side) tested main effects and interactions (P .05) for the RMS amplitude and PC scores from the temporal waveforms. Bonferroni post-hoc analyses tested pair-wise differences. Results: There were no between-group differences for the pelvic motions. Three PC patterns captured 85% of the variance in the waveforms. The external oblique (EO) RMS amplitudes were significantly (P .05) higher than those of the other 3 muscle sites, similar for the PC1 scores which captured overall amplitude. The PC2 score for the internal oblique (IO) was significantly higher (P .05) than that of all other muscles, illustrating a higher initial amplitude compared with later in the movement. There was a significant group by muscle interaction for PC3 scores, demonstrating group differences in temporal patterns. Conclusions: Both groups were able to minimize lumbopelvic motion and recruited their abdominal muscles to similar overall amplitudes, with the IO muscle activated to higher amplitudes early in the movement task. The older adult group demonstrated a distinctive drop in abdominal activity during the leg-lowering phase of the exercise and less symmetry among muscle sites.