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There is no abstract available for this thesis. / Department of Art

Slips, trips, and falls are the costliest source of disabling injuries in the workplace, costing $18.6 billion annually. The purpose of this study was to investigate the effects of mental fatigue on gait variables associated with the risk of slipping and tripping. The study also investigated the efficacy of a 10-minute rest break in mitigating the effect of mental fatigue on those variables. Twenty healthy young adults (10 males and 10 females) participated and completed two experimental sessions. The order of sessions was counter-balanced for each participant. During the mental fatigue session, participants completed a computerized mentally fatiguing task for 90 minutes and performed a set of gait trials every 15 minutes throughout the task. During the control session, participants watched an emotionally neutral documentary in place of the mentally fatiguing task. After 90 minutes of the task or documentary, participants took a 10- minute break and then completed one last set of gait trials. Risk of slipping was inferred from the required coefficient of friction, heel contact velocity, and heel contact angle. Risk of tripping was inferred from minimum toe clearance and obstacle clearance. The results showed no increase in slip or trip risk. Rest breaks appeared to decrease levels of self-reported mental fatigue. However, they did not appear to have any mitigating effect on any of the gait variables that were measured. / Master of Science / Slips, trips, and falls are the costliest source of disabling injuries in the workplace, costing $18.6 billion annually. The purpose of this study was to measure the effect of mental fatigue on the risk of falling. In this study, twenty healthy young adults (10 males and 10 females) completed two sessions. In the first session, the participants completed multiple walking sessions while performing a mentally fatiguing task. In the second session, the participants identical walking sessions, with the exception that instead of performing a mentally fatiguing task, they were watching a documentary. The study also aimed to study whether a 10-minute rest break could reduce the effect of mental fatigue on the participants' risk of falling. The results showed that mental fatigue had no effect on slip or trip risk. The rest break was successful at decreasing the self-reported mental fatigue rating but had no effect on the risk of slipping or tripping.

Falls due to slipping are a serious occupational concern. Slipping is estimated to cause 40-50% of all fall-related injuries. In 2011, falls resulted in 22% of injuries requiring days away from work. Epidemiological data indicates that older and obese adults experience more falls than young, non-obese individuals. An increasingly heavier and older workforce may be exacerbating the problem of slip-induced falls in the workplace. The purpose of this study was to examine the effects of obesity and age on slip severity and fall outcome following an unexpected slip. Four groups of participants (young obese, young non-obese, older obese, older non-obese) were exposed to an unexpected slip perturbation. Slip severity (slip distance, slip duration, average slip velocity and peak slip velocity) and slip outcome (fall or recovery) were compared between groups. Obese individuals experienced 8.25% faster slips than non-obese individuals in terms of average slip velocity (p=0.022). Obesity did not affect slip distance, slip duration or peak slip velocity. Obese individuals also experienced more falls; 33.3% of obese individuals fell compared to 8.6% of non-obese (p=0.005). Obese individuals were 8.24 times more likely to experience a fall than non-obese individuals, when adjusting for age, gender and gait speed. No age effects were found for slip severity or slip outcome. This study revealed that obese participants experienced faster slips and more falls than their non-obese counterparts. These results, along with epidemiological data reporting higher fall rates among the obese, indicate that obesity may be a significant risk factor for experiencing slip-induced fall. / Master of Science

Many of our daily activities are achieved through goal-oriented routines which illustrates the adaptability and efficiency of information processing. Nevertheless, slips of action do occur. This study was designed to determine if slips of action can be induced in a well learned task and if so, how these slips affect specific indicators of task performance. Thirty (12 male) right-handed undergraduate participants were taught, with arrow cues, a sequence of dominant hand movements. Following this learning phase, a portion of the sequences were altered by either changing the spatial location of the arrow cue or by changing the actual movement goal. Results revealed that participants made numerous action slips which were most prevalent when the movement goal was altered. This suggests that participants were unable to disengage their expected movement plan and thus were vulnerable to errors. In addition to exploring the frequency of action slips we also looked at participants’ reaction and movement times on trials that preceded and followed errors and found that a speed-accuracy trade-off could not account for the slips. We also showed that frequency of slips on our task could reliably predict performance on the SART, a measure of inhibitory control, and the frequency of attention failures in daily living on the ARCES. Overall, the results of this study reveal that action slips can be induced by manipulating a well learned action routine and that the frequency of these induced slips reflects a participant’s tendency to commit action slips in everyday life.

Many of our daily activities are achieved through goal-oriented routines which illustrates the adaptability and efficiency of information processing. Nevertheless, slips of action do occur. This study was designed to determine if slips of action can be induced in a well learned task and if so, how these slips affect specific indicators of task performance. Thirty (12 male) right-handed undergraduate participants were taught, with arrow cues, a sequence of dominant hand movements. Following this learning phase, a portion of the sequences were altered by either changing the spatial location of the arrow cue or by changing the actual movement goal. Results revealed that participants made numerous action slips which were most prevalent when the movement goal was altered. This suggests that participants were unable to disengage their expected movement plan and thus were vulnerable to errors. In addition to exploring the frequency of action slips we also looked at participants’ reaction and movement times on trials that preceded and followed errors and found that a speed-accuracy trade-off could not account for the slips. We also showed that frequency of slips on our task could reliably predict performance on the SART, a measure of inhibitory control, and the frequency of attention failures in daily living on the ARCES. Overall, the results of this study reveal that action slips can be induced by manipulating a well learned action routine and that the frequency of these induced slips reflects a participant’s tendency to commit action slips in everyday life.

Current winter footwear provides inadequate protection from slip-related injuries on ice, and there is limited research investigating the optimal design of anti-slip devices. This study examined how ice cleat spike height and position in the heel affect slipping. No differences could be observed between spike conditions, but results demonstrated that heel spikes may prevent slips initiated between heel contact and foot-flat and forefoot spikes may be necessary to prevent foot-flat slips. Further analysis compared slip outcomes measured using two slip onset definitions: 1) heel contact, and 2) the first point of increasing positive heel acceleration. Slip onset defined as time of heel contact overestimated the number of slips and slip distances. These results demonstrate that ice cleats have the potential to protect pedestrians from slipping but some styles available to consumers (i.e. heel spikes only) may not be adequate. Choice of slip definition in footwear evaluations can significantly influence study outcomes.

Current winter footwear provides inadequate protection from slip-related injuries on ice, and there is limited research investigating the optimal design of anti-slip devices. This study examined how ice cleat spike height and position in the heel affect slipping. No differences could be observed between spike conditions, but results demonstrated that heel spikes may prevent slips initiated between heel contact and foot-flat and forefoot spikes may be necessary to prevent foot-flat slips. Further analysis compared slip outcomes measured using two slip onset definitions: 1) heel contact, and 2) the first point of increasing positive heel acceleration. Slip onset defined as time of heel contact overestimated the number of slips and slip distances. These results demonstrate that ice cleats have the potential to protect pedestrians from slipping but some styles available to consumers (i.e. heel spikes only) may not be adequate. Choice of slip definition in footwear evaluations can significantly influence study outcomes.

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

Research Objectives The objective of this study was to evaluate if neuromusculoskeletal training (i.e., weight and balance training) for older adults could reduce the likelihood of slip-induced fall accidents. The study focused on evaluating biomechanics among the elderly at pre- and post-training stages during processes associated with slip-induced fall accidents. Motivations: Older adults are at a higher risk of falls due to deficient gait characteristics and postural control, especially when facing unexpected external perturbations such as slippery surfaces. The literature (Alexander et al., 1992; Englander 1996; Hausdorff, 2001; Rizzo 1998) indicates that falls among the elderly over 65 result in enormous economic and personal losses, therefore, the losses must be diminished. The results from this study can provide intervention strategies for researchers, health care individuals, and the elderly and their families in reducing the likelihood of slip-induced falls. Background: More than 25% of older adults fall every year (Sattin, 1992), and older adults and their family members fear their falls and fall-related injuries due to the associated high mortality rate (Jensen, 2003). The Center for Disease Control (CDC) reported in 2003 that emergency departments treated more than 1.6 million seniors due to fall-related injuries and, among them, 373,000 were admitted to the hospital. In 2002, The National Safety Council reported that 14,500 people died due to fall-related accidents, and 60 percent of them were 65 years of age and older. To minimize economic and personal losses, tribometric techniques for assessing shoe/floor interactions, the biomechanical responses in walking on slippery floor surfaces, and postural control were studied. Still, the elderly population is at a high risk of falling, severe enough that it is a major cause of hospitalization (CDC, 2003). Yet reasons for slip-induced fall accidents are not clear. Therefore, mechanisms involving fall accidents must be explored and, further, interventions to minimize fall accidents must be discovered and implemented. The occurrence of falls among the elderly are postulated to result from neuromusculoskeletal aging. The changes in neuromusculoskeletal components with advancing age are commonly accompanied with mobility problems and poor health status contributing to a decreased physical capability such as a reduction in lower extremity strength (Larsson et al., 1979; Lord et al., 1991 and 1994; Murray et al. 1985; Stalberg et al., 1989; Whipple et al. 1987) and insecure and unconfident balance (Manchester et al. 1989; Stelmach and Sirica, 1987; Teasdale et al. 1991; Thelen et al., 1998; Woolacott, 1986) leading to unstable dynamic postural control and poor gait dynamics (Alexander, 1994; Judge, 2003; Lockhart et al., 2003; Wolfson, 2001). Unstable dynamic postural control and poor gait dynamics influence the likelihood of falls among older adults (Guralnik et al.1994; Judge et al.1996; Lockhart et al., 2003; Tinetti et al. 1988). Therefore, in an effort to improve unstable dynamic postural control and poor gait dynamics, strength and balance training have been proposed and implemented. (Campbell et al., 1999; Day et al., 2002; Fiatarone et al., 1994; Neil, 1994; Shepard et al., 1993; Tinetti et al, 1994; Wolfson et al, 1993). Problem Statement: Although the significance of muscle strengthening and balance training in reducing falls for older adults has been addressed previously, most studies (Berg et al., 1992; Duncan et al., 1990; Guralnik et al.,1994; Hageman et al., 1995; Nashner, 1993; Nashner and McCollum, 1985; Nevitt et al., 1989; Overstall et al., 1977; Rikli and Jones, 1999; Tinetti, 1986) have focused on the effect of muscle strengthening and balance training on the static and dynamic postural control such as quite standing, one-leg stand, the sit-to-stand test, the test of precise movement, functional reaching, or the mobility test. Yet, research to evaluate the effectiveness of muscle strengthening and balance training on actual slip-induced fall events was lacking. This study were carried out to evaluate the likelihood of falls at pre- and post stages of training by incorporating and validating the effectiveness of training utilizing actual perturbations commonly associated with slips and falls. Method: 18 older adults participated in the study for 8 weeks: 6 individuals in balance group, 6 individuals in weight group, and 6 individuals in control group (social group). Each group met three times a week and each session lasted for 1 hour. Biomechanical dependent measures and psychosocial dependent measures were evaluated to the effects of training. Results: The results indicated that, overall, training resulted in improvements in biomechanical dependent measures. Further, regular social activities resulted in improvements in proprioception sensory sensitivity and in ankle dorsiflexion muscular strength. Conclusion: Balance training contributed to an improvement in ankle flexibility, whereas, weight training did not contribute to an improvement in ankle flexibility although either weight or balance training played a role in decreasing slip-propensity and the likelihood of slip-induced falls among older adults. An ability to integrate neuro-musculo-skeletal systems was improved by training and was a main contributor in reducing the likelihood of slip-induced falls. Proprioception sensitivity by itself did not play a role in decreasing the likelihood of slip-induced falls. In addition, the exercise training as well as social activities played a role in altering psychosocial behavior (i.e. fear of falling and independency) of older adults. The author concluded that an ability to integrate neuro-musculo-skeletal systems could be improved by either balance or weight training and could be a primary factor contributing to a reduction in the likelihood of slip-induced falls among older adults. In addition, the author concluded that the regular social activities also could contribute to an enhancement in the psychosocial characteristics of older adults. / Ph. D.