Changes in Perceived Comfort, Strength and Electromyographic Response in Lower Back, Hip and Leg Muscles during 8-Hour Prolonged Sitting

Abstract

Many occupations require workers to sit for an extended period of time. This study investigated the changes in perceived comfort, strength and electromyographic (EMG) activity of 14 lower back, hip and leg muscles during prolonged sitting. Twenty-five subjects (13 males) sat of a chair for eight hours. Subjects could move freely on the chair and engage in sedentary activities such as reading. At baseline and every one-hour interval (h0 – h8), subject’s perceived comfort at the back, hips and legs, together with the maximum isometric back extension torque and the EMG pattern of 14 muscles were assessed. The root mean squared magnitude and the median frequency of the power spectrum of the EMG signals were calculated. As sitting time increased, subjects showed increased level of discomfort for the lower back (P = 0.002), hip (P < 0.001) and leg (P < 0.001) muscles. At the hip, males indicated more discomfort than females over time (sex× time interaction: P = 0.049). Back extension torque declined with increasing sitting time (P = 0.044). The average torque during the second half (h5 – h8) of the sitting period decreased by 9.3% (P = 0.007) compared with the first half (h0 - h4). Overall, no consistent change in EMG pattern was observed. For most muscle groups, there was no effect of time or sex on EMG magnitude or median frequency. In conclusion, prolonged 8-hour sitting lead to slightly increased discomfort and reduced strength. Muscular fatigue resulting from quiet sitting may be too subtle to be detected by surface EMG.