PURPOSE: The purpose of this investigation was to identify dynamic stability during initial contact when there is a risk of a slip and toe off when there is a risk of a trip as defined by the location of the vertical projection of the center of mass (COM) in the medial-lateral (ML) direction to the base of support (BOS) (Patla 1995). SUBJECTS: Sixteen individuals who were between 65 to 85 years who did not use any assistive device, had no chronic musculoskeletal problems in the lower limbs, joint arthroplasty, or, new medical condition within the past month interfering with walking. METHODS: The VICON 370 3D motion analysis system was used to collect whole body kinematics with a 14 segment model for the calculation of COM in the ML direction and identification of the BOS for each foot. Ten walking trials on a 30-foot walkway were collected; the first three trials having the most optimal marker visibility were processed, averaged and used for data analysis. Dynamic stability at initial contact was measured as the average percentage location of the vertical projection of the COM to the BOS in the ML direction for each leading limb condition. Values greater than 50% indicated a location of the COM toward the left and less than 50% toward the right. Dynamic stability during toe off was the distance (cm) from the midpoint of the supporting foot to the vertical projection of the COM. ANALYSIS: Two paired t-tests were performed to evaluate for differences in side for both initial contact and toe off using SPSS 10.0. RESULTS: The location of the COM was to the left of midline with the right limb (M = 61, SD = 6.6%) initial contact and to the right of midline for the left limb (M = 42, SD = 7.5%), a statistically significant difference (t (15) = 7.8, p < .0001). The average location of the COM to the BOS was medial to the midpoint of the foot at toe off for the right limb (M = 3.57, SD = 1.21cm) and the left limb (M = 4.20, SD = 1.43cm), with no statistical difference between limbs (t(15) = -1.57, p = .138). CONCLUSION: These results indicate that dynamic stability at initial contact in individuals 65 to 85 is stable when the COM is held slightly toward the trailing limb (10%) and at toe off when the COM is medial to the supporting limb (3 to 4 cm).

1. Patla, A. E. (1995). A framework for understanding mobility problems in the elderly. In Craik, R.L., & Oatis C.A. (Eds.). Gait Analysis Theory and Application. 436-449). New York: Mosby

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