Handling objects in old age

Healthy aging influences peripheral and central levels of the neuromotor system. These age-related changes contribute to the decline in dexterous manual behavior. Difficulty in performing activities of daily living increases reliance on external assistance. Understanding specific mechanisms leading to the decline in fine manual performance is crucial for their rehabilitation. In this thesis, we have attempted to increase our awareness of the causes underlying manual disability in old age. The first study investigated how old adults apply forces and moments on a freely-movable object using a precision grip (thumb and index finger) during functionally-relevant tasks. During the grasp-lift task old adults misaligned their thumb and finger contacts and produced greater grip force, greater external moments on the object around its roll axis, and oriented force vectors differently compared with young adults. During a precisionorientation task of inserting a slot on the object over a bar (‘key-slot’ task), old adults were more variable in digit-tip force directions and performed the key-slot task more slowly. With practice old adults aligned their digits, reduced their grip force, and minimized external moments on the object. We conclude that with old age comes with a reduced ability to control the forces and moments applied to objects during precision grasp and manipulation. This may contribute to the ubiquitous slowing and deteriorating manual dexterity in healthy aging. Another study investigated the effects of transcranial direct current stimulation (tDCS) to the contralateral M1 combined with motor training (MP) on changes in the forces applied to the object during grasp and manipulation. We also measured performances on functional tasks in healthy elderly