AGE-RELATED-CHANGES IN BALANCE CONTROL-SYSTEM - INITIATION OF STEPPING

The balance control system of a group of healthy and fit, young and el derly subjects was studied during the initiation of stepping in one of three directions: forward, sideways, and backwards in response to a l ight cue. The performance of these movements requires shifting support from two to one foot, moving the centre of mass outside the initial b ase of support and creating a new support configuration. By recording and analysing the vertical ground reaction force beneath the subject's stepping foot, we were able to examine the two phases prior to limb l ift-off for stepping: reaction time and weight transfer time. Both rea ction time and weight transfer time increased with age: The elderly su bjects had a proportionately larger increase in weight transfer time c ompared to the reaction time. The peak force generated showed an age b y stepping direction effect: the elderly had a significantly lower pea k force for the forwards stepping compared to the younger subjects. Th e larger increase in weight transfer results in a slower stepping resp onse. Since a stepping task is often recruited to avoid a fall, the in crease in response execution time can have undesirable consequences.