There is a greater risk of hip fracture if an individual falls, does not recover, and impacts on the hip. Despite this, until recently, there have been few studies on motion in the lateral-medial plane, on the biomechanics of large postural disturbances, and on the descent or impact phases of falls.

We hypothesized that there exists a disturbance threshold (the magnitude of a disturbance that is just sufficient to prevent recovery) that depends on lower extremity strength, reaction time and recovery capabilities. We also hypothesized that certain disturbances are more likely to result in an impact on the hip and that fast walking speed is protective against impacting on the hip.

Using both experiments and computer simulations, we determined the disturbance threshold of a trip as a function of strength, reaction time and recovery capabilities, by increasing the magnitude of a trip, or trip hold duration, until recovery was no longer possible. We also assessed the effect of disturbance type and gait speed on fall direction, impact location and impact velocity by studying four disturbances (faint, slip, step, trip) and three gait speeds (fast, normal, slow) without recovery.

For the trip, there exists a disturbance threshold that depends on lower extremity strength, reaction time and recovery capabilities. Compared to other disturbances and gait speeds, slipping or fainting while walking slowly was more likely to result in an impact on the hip, suggesting a greater risk for hip fracture. Finally, fall and fall-arresting attempt simulations using the ATB model provide an excellent alternative research tool to experiments with volunteers.

High-risk fallers are individuals with slow reaction times, small recovery capabilities and weak strengths since they are less capable of recovering. Highrisk fall situations are disturbance magnitudes that are greater than an individual’s disturbance threshold since he is, in general, unable to recover. Moreover, individuals with reduced gait speed and who are unable to make any fall-arresting attempts are also high-risk fallers since they are more likely to impact the hip. Slips and faints are also high-risk fall situations since they are more likely to result in an impact on the hip.