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Trailing leg postural strategies during slipping.

Cham-R; Moyer-B; Redfern-MS
ISPGR 2007, Proceedings of the 18th International Society for Posture & Gait Research, July 14-18, 2007, Burlington, Vermont. Victoria, BC Canada: International Society for Posture & Gait Research, 2007 Jul; :161
Same-level falls precipitated by slipping are among the leading causes of disability in the elderly. Legs, trunk and arms all contribute to the complex slip-initiated postural response.While the response of the leading leg, i.e. slipping leg, has been previously described, a precise characterization of the trailing leg strategies is lacking and this information is important to understand the human factors contributing to the increased risk of slips/falls in older adults. Thus, the goal of this study is to identify the trailing leg postural strategies during slipping, and to investigate whether these strategies are coordinated with the leading leg response. Methods: Thirteen older (55-67 years old) and 15 younger (20-33 years old) healthy subjects participated in this gait study. To ensure natural walking, participants were informed that the first few trials would be non-slippery. Two or three dry trials were collected ("baseline"). Then, without the participant's knowledge, a glycerol solution was applied onto the floor and another gait trial was conducted ("unexpected slip"). Full body motion and bilateral ground reaction forces were collected. A custom developed 15 segment whole body model was utilized to derive joint angles and moments using inverse dynamics approaches. Results: Four strategies termed minimum (MIN), foot-flat (FF), mid-flight (MID), and toe-down (TD) were identified based on the trailing foot flight distance/duration and the trailing foot orientation upon contact with the floor. MIN patterns are the least severe slips and TD responses are the most severe slips (p = 0.01). A statistically significant correlation was found between the type of trailing leg strategy and the moment generated by the knee of the leading leg during slipping (p < 0.01). Specifically, a reduced extension moment at the knee of the leading leg during slipping appears to be correlated with a greater risk of responding with a TD pattern. Also, subjects who normally (known dry environments) walk with a reduced extension hip moment in the stance leg at contralateral toe off experienced a toe down slip pattern when the floor was contaminated (p < 0.01). Finally, age group effects were not statistically significant. Conclusions: Thus, trailing leg strategies appear to play an important role in slip-initiated recovery responses. The findings of this study suggest the selection of trailing leg strategies depend both on the response generated by the leading leg after a slip is initiated but also on typical normal walking patterns on dry floors. No age effects were found in this study, perhaps because the older group of participants was healthy and not very old. However, the results also suggest that motor responses that may be affected by aging, e.g. walking with a reduced knee/hip extension moment, may aggravate the risk of experiencing a TD slip pattern (most severe slip).
Humans; Men; Women; Age-groups; Walking-surfaces; Floors; Musculoskeletal-system; Physiological-factors; Physiological-function; Physiological-response; Posture
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Grant-Number-R03-OH-007533; Grant-Number-R01-OH-007592
Source Name
ISPGR 2007, Proceedings of the 18th International Society for Posture & Gait Research, July 14-18, 2007, Burlington, Vermont
Performing Organization
University of Pittsburgh, Pittsburgh, Pennsylvania