Aging effects on the coordination of grasping and walking

Manual dexterity often declines with aging and leads to difficulties and increased dependency in daily tasks involving object manipulation such as preparing meals or shopping. Successful object manipulation requires a precise fingertip force control. Older adults use excessive grip forces, but maintain the ability for anticipatory force control during simple object manipulation. It is unclear if anticipatory control is maintained in complex tasks such as object transport while walking. This task involves attention sharing between grasping and walking and inter-segmental coordination to dampen gait-induced object perturbations. Therefore, the purpose of this study was to investigate aging effects on grasp control during object transport while walking. Twelve healthy older and 12 younger adults transported a grip instrument during unperturbed walking and when walking was perturbed by crossing an obstacle or changing step-lengths. Grip (normal) and gait-induced (tangential) inertial forces were measured. While the grip-inertial force ratio was higher in the older subjects, they showed a strong grip-inertial force coupling comparable to that of the young during unperturbed walking. No age-related change in the force coupling was seen during step-length changes. However, during obstacle crossing, the forces in the older group were less tightly coupled as seen by increased time lags of grip relative to inertial force peaks. Moreover, the force ratio in the older group increased further. In the older, but not the younger group, time lags during obstacle crossing were correlated with the amount of physical activity such that more active older subjects had lower lags. These findings indicate that older adults maintain anticipatory grasp control during walking with an object, while being less efficient in the amount of grip force employed. Age-related changes in anticipatory control emerge only with increasing task difficulty, i.e., obstacle crossing. These changes may be indicative of dual-task interference. Our findings highlight the need to study grasp control within complex tasks to better understand difficulties encountered by older adults in daily life. The relationship between physical activity and anticipatory control provide further rationale to promote physical activity in older adults to maintain or improve functional tasks such as walking with object transport in challenging environments.