Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-007592, 2009 Sep; :1-28
Slip and fall accidents are among the leading generators of injuries in the workplace, especially among older adults. The aging dynamics of the work force have motivated the long-term goal of this proposed study, that is to reduce slip-precipitated falls among older workers. Understanding the biomechanical reasons for the increased incidence of slip and fall accidents in older workers is required knowledge to achieve the long-term goal of this project. The first set of results (related to Specific Aims 1 and 2) characterizes the trailing leg's biomechanical response to slips. Healthy participants divided into two age groups (20-33 years and 55-67 years) were asked to walk in two conditions: a known dry floor and a glycerol-contaminated floor expected to be dry, inducing an unexpected slip of the leading foot at heel contact. Four slip-related trailing leg response strategies were identified, ranging from a minimal disruption of the swing phase to a premature (approximately 50 ms after toe off) interruption of the swing phase. Aging effects were minimal. The response of the leading/slipping leg preceded that of the trailing limb. The magnitude of the trailing leg's response was associated with that of the knee in the leading/slipping leg, suggesting interlimb coordination. The corrective moment at the knee of the trailing leg was also correlated with that measured at the hip in the same leg, suggesting intralimb coordination. The specific trailing leg's strategy used in a slip is partially determined by preslip walking patterns and early stance slip dynamics. The second set of results (related to Specific Aim 3) confirms our previously reported findings associated with slippery floor warning. Specifically, when warned about the potential of encountering a slippery floor, both young and older adults increase cadence, which has been correlated with a lower risk of slipping and falling. As a result, the duration of the sub-phases of the gait cycle, e.g. single/double support, stance, stride, are all reduced when warned about the possibility of encountering a slippery floor. Gait speed was increased especially in the young group of subjects and this finding can be attributed to the increase in cadence. Step width was reduced when warned about slippery floors. This result is believed to be due to the increase in cadence as well. Finally, surprisingly, The first goal of Specific Aim 4 was to investigate the relationship between lower extremity strength capabilities and slip severity. Reduced muscle strength has been 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 young and 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 shortly after heel contact onto the contaminated floor. Analyses revealed significantly greater left knee extension RTD and angular impulse in young males experiencing non-hazardous compared to participants who experience hazardous slips. Findings were not evident in older subjects, 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. The second goal of Specific Aim 4 was to investigate the association between ability to integrate sensory information important for balance and slip severity. Decreased postural stability has also associated with aging and falls. The Sensory Organization Test (SOT) was administered and the amount and average velocity of body sway were calculated for each condition based on the center of pressure standard deviation (COP ST DEV) and path length (PATH LENGTH), respectively. COP ST DEV and PATH LENGTH were each regressed on age group and hazardousness within condition. Significantly greater PATH LENGTH in Condition 4, in which somatosensation was rendered inaccurate, were evident in individuals experiencing hazardous compared to participants who experienced 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.