Grasping changes in healthy older adults: adaptations in motor control

With advanced age comes decline in motor function, including a reduced capacity to perform activities of daily living (ADL) such as cooking, eating and dressing. The ability to grasp and manipulate objects forms an integral part of performing ADL, with some tasks requiring one hand (unimanual) and other tasks requiring the coordinated use of both hands (bimanual), however both unimanual and bimanual grasping are affected as a result of ageing. The aim of this thesis was to better understand changes in unimanual and bimanual grasping in older adults (OA) and how these changes relate to reduced manual dexterity observed in OA. The first experiment documents the building of a portable, bimanual manipulandum system that can be used to assess grasping in OA. The second experiment explored differences in unimanual and bimanual grasping between younger adults and OA using a grasp-lift-replace paradigm. The results show OA exhibit: i) slower grasping strategies with higher levels of grip force, ii) reduced anticipatory control and iii) changes in distal, upper-limb muscle activation patterns during initial stages of the grasp and lift. These changes were apparent across unimanual and bimanual grasping tasks. In experiment three OA were stratified into subgroups displaying good and poor levels of manual dexterity. Results from the grasp-lift-replace paradigm found that both OA groups showed slower lifting strategies and elevated grip force profiles compared to younger adults. However, measures of reduced anticipatory control were the only statistically significant (p < 0.05) grasping variables separating OA groups with good and poor levels of manual dexterity. Changes in distal, upper-limb muscle activation patterns were also evident within the OA group exhibiting poor levels of manual dexterity. The findings from this thesis demonstrate OA show slower, more cautious grasping strategies, but these changes are not indicative of reduced manual dexterity. Age-related decline in manual dexterity is better explained by reduced levels of anticipatory control, that may be a result of changes to underlying muscle activation patterns during grasping.