Forward-backward postural protective stepping responses in young and elderly adults.

OBJECTIVES: Protective steps are essential for fall avoidance. Most studies only examined forwards stepping despite considerable bio-mechanical and visual differences between the forwards and backwards directions. We assess forward-backward differences in protective steps in a young and elderly group.

METHODS: Protective stepping responses were elicited by a platform moving unpredictably either forwards or backwards. For control purposes, voluntary steps, in response to vibration cues on the forehead or occiput were also recorded. Reaction time (RT), length and angular velocity of the steps were measured in 13 young (age 19-35years) and 13 elderly (age 58-86years) healthy volunteers.

RESULTS: (i) Protective vs voluntary steps: protective steps were earlier, faster and longer than voluntary steps. (ii) Forwards-backwards differences: RT was quicker for backwards than forwards protective steps, in contrast to voluntary steps where RTs were similar in the two directions. (iii) Age difference: the elderly had universally slower steps and they generated shorter backwards than forwards protective steps.

CONCLUSIONS: Protective steps appear more robust than voluntary steps - they are earlier (shorter RT), longer and faster than voluntary steps, indicating an automatic rather than a volitional reaction. Backwards protective steps occur earlier than forwards; such promptness may have evolved out of bio-mechanical features which make falling backwards easier. Since our elderly subjects had an average age <70years, their slower and shorter protective backwards steps may represent the first abnormality in this rescue postural response. The findings in the elderly may partly depend on dysfunction in fronto-basal ganglia postural loops.