No abstract

While it is generally recognized that prolonged sitting periods at work can harm the locomotor system, little attention has been paid to the impact of sitting behavior on muscle stiffness. This study investigated the effect of sitting posture and postural activity on lower back muscle stiffness in a controlled experiment in which participants sat at a desk for 4.5 h. Lower back muscle stiffness was measured before and after the sitting period. In addition, continuous recording of kinematic data of the lower back using an eight-camera motion analysis system was applied to quantify sitting posture and the level of postural activity. The results show that the prolonged sitting period led to a significant increase in muscle stiffness. Further, all participants spent a substantial amount of time in a slumped sitting posture, and the level of postural activity varied significantly throughout the 4.5 h sitting period. Those results suggest that the increase in lumbar muscle stiffness is presumably related to the often-preferred slump sitting posture and may help to understand how prolonged sitting periods can increase susceptibility to common pathological conditions such as low back pain. However, the results also leave some uncertainties that need further investigation.

In modern Western societies, sedentary behavior has become a growing health concern. There is increasing evidence that prolonged sitting periods can be associated with musculoskeletal disorders. While it is generally recognized that back muscle activity is low during chair-sitting, little is known about the consequences of minor to no muscle activity on muscle stiffness. Muscle stiffness may play an important role in musculoskeletal health. This study investigated the effects of regular muscle contractions on muscle stiffness in a controlled experiment in which participants sat for 4.5 h. Neuromuscular electrical stimulation in the lumbar region of the back was applied to trigger regular muscle contractions. Using stiffness measurements and continuous motion capturing, we found that prolonged sitting periods without regular muscle contractions significantly increased back muscle stiffness. Moreover, we were able to show that regular muscle contractions can prevent those effects. Our results highlight the importance of consistent muscle activity throughout the day and may help explain why prolonged periods of chair-sitting increase the susceptibility to common pathological conditions such as low back pain.