Falls are the leading source of injury for all ages, and for older adults are the primary cause of injury related death. Loss of foot to ground traction accounts for 25-40% of falls, typically referred to as a slip. Slips alter the relationship between center of mass and lower limb base of support resulting in altered whole-body angular momentum and inability to support body weight due to loss of stability. But not all slips lead to falls. Stability may be recovered through a combination of response movements, such as swinging the arms or rapid recovery steps. Stability must be recovered quickly otherwise insufficient bodyweight support rapidly leads to a damaging ground collision. A high percentage of falls result in fractures, contusions and sprains to both the trunk and limbs, while slips disproportionately cause lower back injuries. A primary goal of fall prevention training is to improve the ability to resist slips using perturbations that mimic the specific sensory and biomechanical context of natural slip events. However, generating lifelike slip perturbations that mimic the diversity of slipping conditions poses a significant hurdle to improving a more general slip resistance ability. Using movement analysis, the investigators will determine the relationships between diverse slip conditions, reactive responses to slips from those conditions, and slip vulnerability across the gait cycle to generate new data that may guide future interventions.

Recent evidence suggests most slip-related falls in daily life happen in diverse slipping conditions where the ground is not level, or the person is turning or changing direction. While slips that occur during straight walking on level ground and the responses to those slips are relatively well understood, very little is known about slips that occur while walking on slopes or curved paths and which reactive responses are effective to prevent falls in such conditions. This limits the ability of clinicians to incorporate a diverse range of slipping experiences into fall prevention interventions. Understanding how reactive responses and slip vulnerability depend on diverse slip conditions may guide future interventions that promote a more general fall resistance to the broader range of slips encountered in the real environment.

This project will determine the impact of turns and slopes on reactive movements and fall vulnerability by determining the effects of path curvature on reactive movements and slip vulnerability at different times in the gait cycle and determining the effects of ground slope on reactive movements and slip vulnerability at difference times in the gait cycle. It is hypothesized that diverse slipping conditions will change the reactive responses involving protective stepping and arm swing and that the distinct dynamics of turns and slopes produce maximum vulnerability to slips at different times in the gait cycle compared to slips during straight walking on level ground. To evaluate these aims, the investigators will administer slip perturbations on slopes that vary in both magnitude and direction, on curved paths that vary in curvature, and with slip onset that varies across early, middle, and late stance. Understanding the relationships between diverse slipping conditions, reactive responses, slip severity and fall vulnerability may guide future research and training interventions towards more comprehensive fall resistance ability.

Inclusion Criteria:

• Age 19-35

Exclusion Criteria:

• Uncontrolled hypertension
• Peripheral arterial disease
• Knee osteoarthritis
• Vertigo
• Meniere's disease
• Chronic dizziness
• History of back or lower extremity injury
• Surgery that affects mobility
• Neurological disease that limits the ability to walk

De-identified individual participant data for all primary and secondary outcome measures will be made available.

Data will be available within 6 months of study completion.

Data access requests should be emailed to the PI.

Up to 4 hours

This protocol was not expected to put participants at risk for Serious Adverse Events, or at risk for All-Cause Mortality.

Fall rates for slipping on slopes are taken from walking trials on a treadmill. The moving treadmill belts require the participants to recover from the slip and continue walking. Therefore, the fall rates we measured are very likely to overestimate the fall rates from slips on slopes during walking overground.