Kim, HD, Brunt D; University of Florida, Gainesville, FL, USA. Kimx0286@ufl.edu.

PURPOSE: The purpose of this study was to determine whether age differences exist in the response to unexpected changes in direction while stepping over obstacles. BACKGROUND: Falls in the elderly are a common and serious health problem due to a significant loss of functional independence. Although there are numerous works documenting the characteristics of obstacle avoidance strategies in young and older adults, studies of perturbations while crossing obstacles are limited. Because of the high prevalence of tripping over obstacles as a cause of falls, more in depth knowledge of dynamic control while stepping over obstacles is needed to improve risk assessment and intervention design. This study was carried out to shed light on how environmental constraints or uncertainty affect the ability of young and older adults to step over obstacles. SUBJECTS: Participants consisted of seven young adults (mean age = 29.8, range = 23-36) and seven healthy elderly adults (mean age = 75.0, range = 65-81) with no known neurological or orthopedic deficits. METHODS: Subjects stepped over an obstacle where heel strike landed on a predetermined target. During random trials a light signal cued the subjects to change their stepping direction to a diagonal target. These visual cues were provided at mean times of 218 ms, 368ms, and 453 ms following the movement onset. ANALYSIS: ANOVA techniques determined the effects of age difference, stepping condition (normal, diagonal) and the timing of the visual cue on medio-lateral (Fy) and anterior-posterior ground reaction forces (Fx) of the stance limb and bilateral gluteus medius (GM) and stance soleus (Sol) EMG responses. RESULTS: There was an increase in Fy following the light signal. There was a significant difference in the onset of Fy between two groups, which was 198 ms for young adults, and 271 ms for elderly adults (p<.001), but the timing of the visual cue did not affect the onset of Fy. Peak Fy and the slope to peak Fy were greater for the young adults (p<.05) and for the late visual cue (p<.05). Fx decreased (deceleration force) as Fy increased. This decrease was greater for the later visual cue. Mean onset of bilateral gluteus medius was 194 ms for young adults and 272 ms for elderly adults (p<.05). Onset of stance soleus was 177 ms for young adults and 242 ms for elderly adults (p<.05). The timing of visual cue, however, did not affect the onset of bilateral gluteus medius and stance soleus. CONCLUSION: These results suggest that unlike young adults, elderly adults did not flexibly modify their responses to unexpected changes in direction while stepping over obstacles. Furthermore, these diminished abilities may partially account for high rates of falls in the elderly. FUNDING SOURCE: None.

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