The biomechanics of slips are commonly studied in laboratory settings in an effort to improve the understanding of slip mechanisms for the advancement of slip and fall prevention strategies and risk assessment methods.  Prior studies have shown changes in gait after slipping, and these changes can reduce the external validity of experimental results.  As such, most researchers only slip participants one time.  The ability to slip participants more than once, after allowing gait to return to a natural baseline, would improve the experimental efficiency of these studies.  Therefore, the goal of this study was to determine the time duration of slip-induced changes in gait. The required coefficient of friction (RCOF), a parameter highly predictive of risk of slipping, was measured on thirty-one young male adults during level gait on three separate days before slipping, immediately (<10 minutes) after slipping, and either one, two, four, or six weeks later.  On average, the RCOF decreased 12% from its baseline value (0.20) after slipping, indicating the adoption of a protective gait with a decreased risk of slipping.  The RCOF data trended toward baseline values 4-6 weeks after the slip experience, but remained statistically different from baseline.  This indicates that the slip-induced gait alterations have long-lasting effects, enduring up to six weeks after the slip experience. / Master of Science

This study was conducted to investigate whether hamstring muscle activation rate could potentially serve as an indicator for slip-induced falls, particularly for older adults. Kinematics (heel contact velocity, walking velocity, slip distance, and step length), kinetics (friction demand), and electromyography (EMG) while walking over a slippery surface were collected and examined in the study. Normalized EMG data were examined in term of activation rate and compared to heel contact velocity. Twenty-eight subjects from two age groups (14 young and 14 elderly) walked across a track with embedded force platforms while wearing a fall arresting harness attached to an arresting rig for safety. In order to obtain realistic unexpected slip-induced fall data, the slippery surface was hidden from the subjects and unexpectedly introduced. The primary objective of the study was to evaluate if hamstring activation rate could be a valid indicator for the initiation of slip-induced falls. The results suggested that hamstring activation rate in younger adults was higher than older adults, whereas, younger adults’ heel contact velocity was not different from older adults. These results suggested that heel contact velocity in younger adults was sufficiently reduced before the heel contact phase of the gait cycle. This could be due to the outcome of higher hamstring activation rate in younger adults in comparison to older adults. However, an equal number of falls in two age groups, in spite of older adults’ slower walking velocity, lower RCOF, shorter slip distance, and slower peak sliding heel velocity, suggested that the recovery phase of the slip-induced fall accidents should be studied further. / Master of Science