Role of angular position of the seat in control of posture in response to external perturbation

The effect of advanced age and stool modification on reaching distance in sitting

[Purpose] Reaching is an important functional ability. We investigated the effect of advanced age and stool modification on sitting reach distance. [Participants and Methods] Twenty-four participants (twelve older adults 70 ± 4 years and twelve young adults 29 ± 4 years) reached forward and laterally while sitting on an adjustable stool with 0°, 10° forward, 10° backward, 10° right or 10° left inclination of the seat, with and without footrest and front, back or side leg support. [Results] The outcome of this exploratory study revealed that young adults reached farther than older adults across all the directions of reach and seat conditions. While the inclined seat was utilized, both young and older adults reached farthest in the forward direction. Additional leg supports allowed to reach further; however, older adults were not able to reach in the forward direction as far as young adults. When reaching in the lateral direction, leg support had minimal effect on the reach distance. [Conclusion] Age affects the sitting functional reach ability. Future research should focus on investigating the efficiency of interventions to enhance performance of functional tasks in sitting older adults.

The Effect of Additional Leg Supports in Control of Posture in Sitting

The objective of the study was to investigate the effect of leg supports on the anticipatory and compensatory postural adjustments of sitting subjects exposed to external perturbations in the anterior-posterior direction. Ten young participants received perturbations applied to the upper body while sitting on a stool with an anterior or posterior leg support and when using a footrest. Electromyographic activities of the trunk and leg muscles and center of pressure displacements were recorded and analyzed during the anticipatory and compensatory phases of postural control. Anticipatory activities were observed in the tibialis anterior, biceps femoris, and erector spinae muscles in the anterior leg support condition. Early onset of muscle activity was observed in the tibialis anterior, biceps femoris, rectus femoris, and erector spinae muscles in the posterior leg support condition compared to the feet support condition. Moreover, to maintain balance participants utilized co-contraction of muscles as the main mechanism of balance control in sitting regardless of the availability of the anterior or posterior leg support. There was no effect of a leg support on center of pressure displacements. The outcome of the study provides a background for future investigations of the effect of leg supports on control of balance in sitting when perturbed.