Hanke TA, Tiberio DT, Kinsella-Shaw J; Department of Physical Therapy, University of Connecticut, Storrs, CT, USA. thanke@midwestern.edu.

PURPOSE: This project examined preferred inter-stride interval (ISI) before and after rhythmic auditory pacing. SUBJECTS: Seven younger adults (YA: mean 22.9 years, SD 2.8), seven middle-aged adults (MA: 48.1, [4.7]) and seven older adults (OA: 72.9, [3.1]) participated. No subject had a history of musculoskeletal or neurological dysfunction. No OA had a history of falling. All OA were screened for general mobility, behavioral functioning, and lower extremity sensation. METHODS: Subjects performed rhythmic unipedal stepping in place to the side (ML) and forward (AP) with their dominant lower limb at a preferred pace prior to and after 6 - 70s. trials of auditory pacing at a range of frequencies. Two AMTI (Watertown, MA) force platforms recorded the ground reaction forces (GRFs) beneath each lower limb. Stepping limb vertical GRF was used to determine ISI. ANALYSES: A 3 x 2 x 2 repeated measures analysis of variance was performed (SPSS 11.5; Chicago, IL) with group (YA, MA, OA) as a between subject factor and step direction (ML, AP) and time (PRE, POST) as within subject factors. RESULTS: Mean ISI (ms.):

There were significant main effects for direction (F(1,18) = 18.577, p < .001) and time (F(1,18) = 62.465, p < .001). A significant time x group interaction was also present (F(2,18) = 6.165, p = .009). OA decreased ISI by 28% for AP stepping and 22% for ML stepping as compared to YA (12% AP; 9% ML) and MA (15% AP; 13% ML). This nearly double reduction in preferred ISI across time for OA likely accounts for the time x group interaction and the non-significant between subjects, main effect for group (F(2,18) = 1.707, p = .210). CONCLUSIONS: Older adults performed unipedal stepping at slower preferred tempos initially but not after a brief bout of pacing. Older adults’ preferred stepping rhythm appears to be sensitively dependent on recent performance. Larger reductions in ISI in OA may have resulted from changes in global "stiffness" reflecting the inter-relation of neural (internal oscillatory processes), biomechanical (visco-elastic properties), and behavioral (attention and perception of tempo) factors. Analysis of postural and stepping limb kinematics is underway. Such rapid and robust changes in performance following auditory pacing may provide directives for training stepping responses in older persons with balance impairment. The candidate mechanisms that account for this warrant further investigation. FUNDING SOURCES: Graduate Research Fellowship in Gerontology, Center on Aging and Human Development, University of Connecticut and Connecticut Physical Therapy Association Research Award.

Copyright 2004 by the American Physical Therapy Association

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