Abstract
BACKGROUND: The chair influences the position of the user in relation to his or her devices. Prolonged static sitting is a frequently mentioned risk factor for low back pain. Seat design, thus, plays an important role in the study of human sitting. Quantitative information is needed on what happens to body when one sits in chairs with different seat depth. OBJECTIVE: To determine the myoelectric activity (EMG) of individual lumbar erector spinae muscles after sitting in chairs with different seat pan depth. METHODS: EMG recordings were taken using surface electrodes placed on the lumbar erector spine muscles of 25 normal, volunteer subjects. EMG recordings for muscle activity were made while the study participants were in a comfortable position and performed the required tasks. The experiments investigated with 3 seat depths according to the 5(th), 50(th) and 95(th) percentiles of the buttock popliteal length. The recorded EMG data were normalized to the maximal voluntary contraction. The mean EMG recording was calculated for each of the 3 chairs tested. A mixed model was used to assess the differences among the situations. RESULTS: A significant (p<0.05) difference was observed between the mean EMG recordings for the 3 tested seat pan depths. EMG activity was higher in seats with the 5(th) and 95(th) percentiles compared with that for the seat with 50(th) percentile of buttock popliteal length depth. CONCLUSION: The seat pan depth used during a comfortable position has a significant effect on the level of myoelectric activity in the lumbar erector spinal muscles. The finding of this study may contribute to our understanding of the biomechanics of sitting.