Trunk and Hip Surface Electromyographic Activity During Maximal Voluntary Isometric Contraction in Adults with Chronic Nonspecific Low Back Pain: A Cross-Sectional Study

Abstract

Chronic nonspecific low back pain (CNSLBP) may be associated with altered trunk and hip muscle activation, although surface electromyographic (sEMG) findings remain heterogeneous across muscles and testing conditions. This cross-sectional study compared bilateral trunk and hip sEMG activity during maximal voluntary isometric contraction (MVIC) between adults with CNSLBP and asymptomatic controls. Forty adults (20 CNSLBP and 20 controls) underwent standardized bilateral sEMG recording of the erector spinae, rectus abdominis, gluteus maximus, and gluteus medius. Participant-level bilateral work average (WAV), work average deviation (WAVDEV), and peak amplitude were analyzed. Non-normally distributed outcomes were compared using exact Mann–Whitney U tests with Hodges–Lehmann location-shift estimates and Holm correction for multiple comparisons. In unadjusted analyses, erector spinae WAV was lower in the CNSLBP group than in controls (51.75 [41.63–88.88] vs 75.50 [66.50–107.50] µV; p=0.026), as was rectus abdominis WAV (60.50 [42.25–86.00] vs 81.25 [60.25–135.63] µV; p=0.040). Erector spinae WAVDEV (p=0.010) and peak amplitude (p=0.043) were also nominally lower, whereas no between-group differences were observed for gluteal WAV. However, none of the comparisons remained statistically significant after Holm correction. Adults with CNSLBP therefore demonstrated nominally lower trunk sEMG activity during MVIC, particularly in the erector spinae and rectus abdominis, but the findings should be interpreted as exploratory rather than as evidence of a generalized or muscle-specific neuromuscular deficit.