The Relationship Between Knee Strength Capabilities, Postural Control and Slip Severity

Slips and falls are serious public health concerns in older populations. Understanding relationships between propensity to slip and biomechanical and physiological characteristics is important to identify factors responsible for slip-initiated falls and to improve slip/fall prevention. Thus, the first goal of this thesis was to investigate the relationship between knee flexion/extension strength and slip severity. Reduced muscle strength is associated with aging and falls. Knee corrective moments generated during slipping assist in balance recovery. Isometric knee flexion/extension peak torque, rate of torque development (RTD), and angular impulse were measured in 30 young and 28 older subjects. Motion data were collected for an unexpected slip during self-paced walking. Slips were characterized as non-hazardous or hazardous based on a 1.0 m/s peak slip velocity threshold measured at the slipping heel. Within-gender regressions relating strength to slip hazardousness and age group revealed significantly greater left knee extension RTD and angular impulse in young males experiencing non-hazardous versus hazardous slips. Findings were not evident in older males, who perhaps implement cautious walking styles, allowing less reliance on post-slip recovery reactions. Other strength variables were not associated with hazardousness. Thus, rapid knee extension force generation may assist balance recovery from hazardous slips.Decreased postural stability is also associated with aging and falls. Therefore, the second goal of this project was to investigate the association between ability to integrate sensoryinformation important for balance and slip severity. The Sensory Organization Test (SOT) was administered and COP standard deviation (COP ST DEV) and path length (PATH LENGTH) were calculated for each condition. COP ST DEV, PATH LENGTH, and variable ratios were regressed on age group and hazardousness within condition. Significantly greater PATH LENGTH and its subsequent effects on ratio variables associated with Condition 4, in which somatosensation was rendered inaccurate, were evident in individuals experiencing hazardous versus non-hazardous slips. Conditions in which vestibular or visual information was rendered inaccurate or missing were not associated with hazardousness. Somatosensory channels detect slips first at the shoe-floor interface and thus may be especially important in early detection and response to a slip