Abstract
Little is known about the landing behavior of the trailing (recovery) foot and ensuing types of falls following a forward slip in walking. The purposes of this study were to (1) determine if community-dwelling older adults experienced bilateral slips at the same rate as had been previously observed for young adults during over-ground walking; (2) determine if fall rate in older adults was dependent on slip type (unilateral vs. bilateral); and (3) identify differences in spatiotemporal variables of the trailing leg step between unilateral and bilateral slips. One-hundred-seventy-four participants experienced an unannounced, unrehearsed slip while walking on a 7-m walkway. Each trial was monitored with a motion capture system and bilateral ground reaction force plates. Although the experimental design, developed with original data from a young adult population, favored bilateral slips, more older adults (35%) than anticipated (10% previously observed in young, p<0.001) displayed a unilateral slip. The probability of fall was equal in the two types of slips. Eighty-two people recovered from the slip, while the remaining 92 (53%) fell. These 92 were classified into two exclusive categories based on the heel distance at the time of fall arrest using cluster analysis: those which resembled a fall into a “splits” position (n=47) or a feet-forward fall (n=45). All (100%) unilateral slips led to splits falls, as expected. Yet, not all bilateral slips (only 83%) resulted in feet-forward falls. A longer forward recovery step with a prolonged step time led to both feet slipping, nearly together, hence a feet-forward fall.
Highlights
Slip-related falls among older adults often lead to self-imposed limitations on independence of daily activities (Zijlstra et al, 2007)
The remaining 33 (70%) were single-step falls (Table 1). Among these falls all (100%) of the 38 unilateral slips resulted in splits falls, while only 45 (83%) of the 54 bilateral slips led to feet-forward falls (Table 1)
While unilateral slips resulted in splits falls, bilateral slips did not, as hypothesized, exclusively lead to feet-forward falls
Summary
Slip-related falls among older adults often lead to self-imposed limitations on independence of daily activities (Zijlstra et al, 2007). Because of the variability associated with the trailing limb behavior, slip-induced falls may take different forms. When one takes a longer step during recovery of stability after slip onset, the recovery limb is more likely to experience a slip as well, resulting in a bilateral slip. In this case, the feet must both be traveling forward, and should remain close together in a feet-forward fall. It is reasonable to assume that a unilateral slip could cause splits of the leading and trailing feet, splits falls, in which the feet remain wide apart, one forward and one behind the torso. Differences in slip-feet kinematics that may lead to different types of falls, may relate to personal characteristics such as age and gender (O'Neill et al, 1994), gait characteristics (Smeesters et al, 2007), an individual’s trunk orientation (Cavagna et al, 1963; Espy et al, 2010b) or hip height at the time of fall (Yang et al, 2009)
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