This thesis describes analysis methods and results from slip-perturbed gait experiments. The risk for falls was related both to the conditions present at heel strike and to the nature of the response. Gait analysis was performed using the Human Movement and Balance Laboratory (HMBL) model, a fifteen segment, fourteen joint model of the human body that was developed as part of this thesis effort. Resulting kinematics and kinetics included three-dimensional angles describing relative segment rotations, segmental and whole-body centers-of-mass, and joint actuation torques for the entire body.

The relationship between pre-slip gait characteristics and the magnitude of slips was explored for both younger and older adults. Slip severity, either hazardous or non-hazardous, was determined using a 1.0 m/s peak slip velocity threshold. Hazardous slips were associated with greater step lengths normalized by leg length, larger and more rapidly changing foot-floor angles at heel strike, and increased cadence across the two subject groups. These results suggest that gait characteristics play an important role in the severity of slips. Older adults were found to walk with shorter step lengths and with smaller and more slowly changing foot-floor angles at heel strike compared to younger subjects, suggesting that age effects also impact slip severity.

The effects of slipping and trailing leg response on slip outcome (falls or recoveries) were explored. Slip severity was found to be the most significant parameter related to outcome. Response strategies were classified, based on trailing leg dynamics, as either minimal, foot-flat, mid-flight, or toe-down. Slipping and trailing leg hip and knee torques were determined using the HMBL model and timing and magnitude parameters from these torques were then identified. Relationships between these parameters, age group (younger/older), response strategy, and outcome were then explored. Age was not found to be significantly related to response strategy or outcome, nor was response strategy found to be related to outcome. Slipping leg knee torque timing and magnitude parameters were related to slip severity and to outcome for hazardous slips. These results suggest that slip responses, coupled with slip severity, determine fall or recovery outcomes.