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Abstract

To reduce the risk of a fall while standing on a moving bus or climbing down the stairs we
intuitively use handles and handrails to augment our balance control. However, a certain
level of adaptation in posture and motor behavior needs to be developed to efficiently
use these aids. This thesis characterizes the influence of holding a handle and making
hand contacts with the environment on whole-body posture and balance recovery in young
adults. A literature review of common strategies for balance recovery and using handles
to augment balance control led to the design of perturbation-based experiments with the
aim to explore balance recovery and adaptation in whole-body posture and to accomplish
the following research goals:
1. To investigate the effects and the underlying mechanism of a supportive hand contact
on postural control during a prolonged exposure of standing balance to perturbations.
2. To examine the mechanisms of assisted balance recovery and the associated loads on
the body when holding a handle mounted at different heights or standing in different
configurations.
3. To investigate the effects of active choice of supportive contacts on motor control.
During continuous perturbations to balance we compared whole-body adjustments and
adaptation in postures with and without additional handle support. A handle was used
to mainly reduce the movement of the body in the posterior direction and merely control
the movement in the anterior direction. Furthermore, whole-body posture, measured by
changes of joint angles, was adjusted to control balance and muscle activity of all postural
muscles highly increased when no handle was used.
By applying an anterior force to the waist we investigated the effectiveness and mechanisms
of balance recovery in five different postures: step stance and normal stance with
or without holding to handles at different heights. Different posture configurations showed
that both step stance and holding to handles at different vertical positions sufficiently assist
balance recovery, compared to normal stance. While there was no significant effect
of handle on displacement of the center of mass, the shoulder height handle required the
lowest handle force, indicating a differential use of the handle. The total body effort was
also reduced with the use of the handle, and the least effort to sustain balance was made
by using the low and shoulder height positioned handle.
To study the effects of contacts an innovative full-body experimental paradigm was
established. To examine adaptation during a reaching task, non-trivial postural perturbations
of the subjects’ support base were systematically introduced. Subjects adapted to
the perturbations by establishing target dependent hand contacts. Moreover, the trunk
motion adapted significantly faster than the motion of the arms. The most striking finding
was that observations of the initial phase of the left arm or trunk motion (100–400
ms) were sufficient to faithfully predict the complete movement of the right arm. Overall,
the results suggest that the goal-directed arm movements determine the supportive arm
motions and that the motion of heavy body parts adapts faster than the light arms.