Article ID: 17-00558
Approximately one in three people over 65 years of age fall each year. The resulting physiological and psychological trauma can lead to physical deconditioning, social isolation and early mortality. Recent research has reported balance recovery can be trained in a single session resulting in dramatic reductions in fall rates. However, most previous research has used repeated exposures to a single hazard in a fixed location and not controlled for reductions in walking speed. It follows, that the biomechanical mechanisms important for reactive balance recovery (in the absence of anticipatory adjustments) are probably not well understood. Here, we investigated the biomechanics of successful reactive balance recovery following the first exposures to unexpected trip and slip hazards in different locations. Ten healthy adults (29.1±5.6 years) completed 32 walks at fixed speed, cadence and step length over a custom 10-meter walkway while being exposed to randomly presented and located slip and trip hazards. Balance recovery kinematics were assessed using a VICON motion analysis system. Repeated exposures to unexpected hazards induced significant reductions (p≤0.05) in anteroposterior (AP) trunk sway following the trips (26.7° to 14.3°; Cohen’s d -1.24) and slips (32.7° to 19.0°; Cohen’s d -0.93). During recovery from unexpected trips, reduced AP trunk sway was strongly correlated with a more posterior centre-of-mass position relative to the stepping foot (r=0.91) and a longer step length (r=-0.71). During recovery from unexpected slips, reduced AP trunk sway was moderately correlated with slower slipping speed (r=0.54) and a less posterior centre-of-mass position relative to the stance (slipping) foot (r=-0.39). The biomechanical mechanisms required for the successful reactive balance recovery from trips and slips were different. Future experimental protocols to optimize reactive balance recovery for fall prevention should therefore use progressive exposures to both slip and trip hazards using specialized equipment and determine if similar biomechanical mechanisms are observed in young and elderly people at risk of falls.