Swing phase interruption in a slip: active or passive response?
Proceedings of the 31st Annual Meeting of the American Society of Biomechanics, August 22-25, 2007, Palo Alto, California. Rochester, MN: American Society of Biomechanics, 2007 Aug; :368
Prevention of slip-precipitated falls requires an understanding of postural reactions to such perturbations. Prior slips/falls gait research has, to a large extent, focused on the leading/slipping leg, while the dynamics of the trailing leg have not been often examined. In Moyer et al. (2007), four types of trailing leg response, termed minimum, foot-flat (FF), mid-flight (MID), and toedown (TD) were identified. Trailing foot toe off occurs in all four patterns. The swing phase is interrupted in FF, MID and TD responses, the focus of this analysis. It may be argued that the swing phase interruption is not an active postural strategy but rather a consequence of the passive dynamics of the fall. Indeed, Tripp et al. (2004) suggested that the direction of the step cannot be modulated after foot lift-off. Thus, the goal of this analysis is to compare the latency of the muscles in the trailing leg with foot floor contact time to determine if the swing phase interruption is an active or passive response. Net joint moments computations revealed that simultaneous hip extension and knee flexion reactions in the trailing limb cause the interruption of the swing phase, lowering the leg onto the ground and decelerating knee extension (Moyer et al., 2007). Thus, compared to normal gait, it is expected that during the slip the magnitude of the hamstring will be greater than that of the vastus lateralis, but that the knee extensors activity will be nonnegligible to prevent limb collapse as body weight is transferred from the leading/slipping leg to the trailing leg. In summary, the latency of the muscles in the upper trailing leg is detected prior to trailing foot floor contact in FF/MID slip patterns. These findings suggest that the swing phase interruption is an active reaction in FF/MID responses. The findings also confirmed that the activity of the trailing leg's hamstring and vastus lateralis plays a role in slip-initiated recovery efforts. The argument of an active swing phase interruption strategy may not hold in TD slip patterns. While the muscular response in the trailing leg may be initiated early, it is likely that the severity of the slip may not allow time for effective active responses, resulting in the fall driving the dynamics of limb collapse.
Fall-protection; Injuries; Injury-prevention; Accident-prevention; Accidents; Physiological-response; Physiological-measurements; Physiological-effects; Physiological-factors; Musculoskeletal-system
Proceedings of the 31st Annual Meeting of the American Society of Biomechanics, August 22-25, 2007, Palo Alto, California
University of Pittsburgh, Pittsburgh, Pennsylvania