The influence of ageing and object properties on prehension

The ability to grasp and manipulate objects is fundamental to many activities of daily living required to maintain independence and quality of life. Physical grip capabilities decline with age; and the functional effect of this can be worsened by environmental barriers. Inclusive design brings a thoughtful approach to the design of products and environments offsetting this decline to ameliorate independent living in later life. As yet, however, little systematic research exists on the effects of object properties on older adults’ reach-­‐to-­‐grasp performance. This thesis addresses that gap by exploring the impact of object friction and size on the reach-­‐to-­‐grasp capabilities of older and younger adults, and how these differ. The research gave an active voice to older adults through focus groups to divulge their difficulties in daily activities that they ascribed to ageing, which provided context to the experimental research. A series of experiments were used to compare the reach-­‐to-­‐grasp behaviour of older and younger adults, and how object size and friction affected this. The research demonstrates that older people adopt slower reach-­‐to-­‐grasp actions in pinch and power grasp, partly due to their lower dexterity. This care, which they acknowledge, is reflected in a more sequential movement, though they exhibit similar grip forces to the younger participants, and participants of all ages scaled their movement and force to object size and friction. Inclusive design sometimes uses impairment simulators, such as the Cambridge Impairment Simulator Gloves, to help designers understand and empathise with impaired grip capability. Accordingly, the research explored the influence of these gloves on the reach-­‐to-­‐grasp behaviour of young adults relative to that of older users. It was found that by lowering young adults’ hand dexterity they forced them to reach-­‐to-­‐grasp performances similar to older adults, allowing the supposition that reduced hand dexterity could partly explain older people’s approach.