The relationship between whole-body motion and upper limb control for reaching and balance

Smith, Craig Paul (2017). The relationship between whole-body motion and upper limb control for reaching and balance. University of Birmingham. Ph.D.

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Abstract

Two functions of the upper limb are reaching and maintaining balance. To successfully perform these roles requires a mechanism for detecting and compensating for body sway. Here I investigate this possible mechanism by using vestibular stimulation to evoke responses in both the upper and lower limbs. I demonstrate that the evoked arm movements are scaled to the degree of sensed whole-body motion, and only operate when reaching within an earth-fixed reference frame. These findings suggest that vestibular signals contribute to maintaining reach accuracy during unexpected body motion which would otherwise take the limb off-target.

I also show that the arm responds to vestibularly sensed body motion for balance. When firmly grasping a stationary support, upper limb forces are coordinated with ground reaction forces to produce a counteractive whole-body sway response. In contrast, during light grasp (<1N grip force) the arm does not actively engage in balance. Instead, it simply acts as a passive sensor to provide feedback of body motion which improves balance. Finally, even though postural control during stance has been successfully modelled as an inverted pendulum, my results suggest that the nervous system does not transform light touch feedback into a signal of rotation about the ankle joint.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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