Effect of seat and table top slope on the biomechanical stress sustained by the musculo-skeletal system.

The purpose of this study was to assess the effect of table and seat slope on the biomechanical stress sustained by the musculo-skeletal system. Angular position of the head and trunk, and surface electromyography of eleven postural muscles were recorded while seated under different conditions of seat slope (0°, 15° forward) and table slope (0°, 20° backward). The specific stress sustained by C7-T1 joint was estimated with isometric torque calculation. The results showed that the backward sloping table was associated with a reduction of neck flexion and neck extensors EMG, contrasting with a concurrent overactivity of the deltoideus. The forward sloping chair induced an anterior pelvic tilt, but also a higher activity of the knee (vasti) and ankle (soleus) extensors. It was concluded that sloping chairs and tables favor a more erect posture of the spine, but entails an undesirable overactivity of upper and lower limbs muscles to prevent the body from sliding.

Sitting on a sloping seat does not reduce the strain sustained by the postural chain.

The objective of this study was to explore the effect of a forward sloping seat on posture and muscular activity of the trunk and lower limbs. To this aim, twelve asymptomatic participants were tested in six conditions varying seat slope (0°, 15° forward) and height (high, medium, low). Angular position of head, trunk and pelvis was assessed with an inertial orientation system, and muscular activity of 11 superficial postural muscles located in the trunk and lower limbs was estimated using normalized EMG. Results showed that a forward sloping seat, compared to a flat seat, induced a greater activity of the soleus (p<0.01), vastus lateralis (p<0.05) and vastus medialis (p<0.05), as well a lower hip flexion (p<0.01). In contrast, no significant variation of head, trunk and pelvis angular position was observed according to seat slope. It was concluded that forward sloping seats increase the load sustained by the lower limbs, without a systematic improvement of body posture.