Abstract
This study investigated the required coefficient of friction (RCOF) and the tangent of center of mass (COM)–center of pressure (COP) angle in the mediolateral (ML) and anteroposterior (AP) directions during turning at different walking speeds. Sixteen healthy young adults (8 males and 8 females) participated in this study. The participants were instructed to conduct trials of straight walking and 90° step and spin turns to the right at each of three self-selected speeds (slow, normal, and fast). The ML and AP directions during turning gait were defined using the orientation of the pelvis to construct a body-fixed reference frame. The RCOF values and COM–COP angle tangent in the ML direction during turning at weight acceptance phase were higher than those during straight walking, and those values increased with increasing walking speed. The ML component of the RCOF and COM–COP tangent values during weight acceptance for step turns were higher than those for spin turns. The mean centripetal force during turning tended to increase with an increase in walking speed and had a strong positive correlation with the RCOF values in the ML direction (R = 0.97 during the weight acceptance phase; R = 0.95 during the push-off phase). Therefore, turning, particularly step turn, is likely to cause lateral slip at weight acceptance because of the increased centripetal force compared with straight walking. Future work should test at-risk population and compare with the present results.
Highlights
Slip-induced falls are the most frequent events leading to injury at home [1,2] and workplaces [3,4]
The magnitude of the mean pelvis rotation angle for spin turns was significantly increased with an increase in the percentage of stance phase compared with step turns, and the mean pelvis rotation angle for spin turns exceeded that of step turns after 50% of the stance phase for all speeds
The results of the present study indicate that the required coefficient of friction (RCOF) values and center of mass (COM)–center of pressure (COP) angle tangent in the ML direction during turning at weight acceptance phase were higher than those during straight walking, and those values increased with increasing walking speed
Summary
Slip-induced falls are the most frequent events leading to injury at home [1,2] and workplaces [3,4]. The tangential force applied to the floor cannot exceed the friction force. The ratio of the tangential force to the vertical force applied to the floor, i.e., traction coefficient, must be lower than the friction coefficient at the shoe–floor interface during the stance phase. The traction coefficient is calculated by dividing the horizontal ground reaction force (GRF) by the vertical GRF. The peak traction coefficients observed just after heel contact [5] and just before toe-off [6] are recognized as the coefficients of friction (RCOFh, RCOFt) required to prevent slips during the braking and propulsion phases, respectively.
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