Effects of sitting posture and duration on lumbosacral nerve root function: A case-control study

Abstract

Purpose: This study aimed to investigate the effects of different sitting postures and prolonged sitting on lumbosacral nerve root function by measuring the amplitude of the soleus (SOL) Hoffmann reflex (H-reflex). Methods: This study included 30 healthy individuals who were selected through convenience sampling and divided according to daily sitting duration over the past year into a prolonged sitting group (≥6 h/day) and a control group (≤4 h/day). The SOL H-reflex amplitude was recorded in erect, slumped, slouched, and supine positions. Ischial pressure was evaluated in all sitting postures to assess spinal loading. Results: Slouched sitting significantly lowered ischial pressure (p < 0.0005) and produced higher H-reflex amplitudes (p < 0.0005), which were not significantly different from those in the supine position (p = 0.362). In contrast, (p < 0.0005) erect and slumped (p < 0.0005) postures showed increased ischial pressure and significantly reduced H-reflex amplitudes (p < 0.0005 for both postures). Participants in the prolonged sitting group demonstrated significantly lower SOL H-reflex amplitudes than those in the control group (p = 0.008, ηp² = 0.23). Conclusion: Various sitting postures and durations exert different effects on the lumbosacral spine and nerve roots. Slouched sitting reduces spinal stress and lower nerve root compression compared to erect and slumped seated positions. Extended sitting duration may partially compress the lumbosacral nerve root, thereby potentially contributing to postural low back pain over time.