Author(s): DHAHBI, W., TAJIK, R., MIMAR, R., KHALEGHI TAZJI, M., STEFANICA, V., Institution: UNIVERSITY OF JENDOUBA, Country: TUNISIA, Abstract-ID: 236

INTRODUCTION:
This investigation evaluated the differential effects of load magnitude and distribution symmetry on trunk neuromuscular activation patterns, vertical ground reaction forces (vGRF), and estimated lumbar spine compression during overground ambulation in individuals with chronic low back pain (CLBP) compared to asymptomatic controls.
METHODS:
Thirty male participants (15 CLBP, 15 controls; age range: 23–28 years) completed walking trials under four experimental conditions: symmetrical and asymmetrical load carriage at 10% and 20% body weight (BW). Bilateral surface electromyography quantified activation from seven trunk muscles (rectus abdominis, external oblique, internal oblique, latissimus dorsi, lumbar erector spinae, multifidus) and the thoracolumbar fascia region, normalized to maximum voluntary isometric contractions (%MVIC). Force platforms recorded vGRF synchronized with heel-strike events. A repeated-measures ANOVA with Bonferroni post-hoc corrections analyzed main effects and interactions of load configuration and magnitude.
RESULTS:
Asymmetrical loading at 20% BW elicited significantly greater peak vGRF relative to symmetrical loading (Δ = 47.3 N, p < 0.001), demonstrating a significant load magnitude × configuration interaction (p = 0.004, ηp² = 0.26). CLBP participants exhibited consistently elevated trunk muscle activation throughout the gait cycle (peak: 37% vs. 30% MVIC in controls; p < 0.001, Cohen's d = 1.68), characterized by maximal recruitment at shortened muscle lengths and 24% diminished activation at optimal length (95% CI: 18.2–29.8%). The lumbar erector spinae and multifidus demonstrated highest activation during asymmetrical 20% BW loading in CLBP participants (0.282 and 0.263 %MVIC, respectively), reflecting compensatory neuromuscular strategies.
CONCLUSION:
Asymmetrical load carriage imposes disproportionately elevated mechanical and neuromuscular demands that are substantially amplified in CLBP populations. These findings provide empirical support for rehabilitation interventions emphasizing optimal load distribution and motor control restoration to mitigate compensatory strain and enhance trunk stabilization capacity.