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

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

Falls are the leading cause of fatal and non-fatal injuries among older adults. Age-related sensory degradation may increase instability and increase the risk of slips and falls in older adults. The integration of three sensory systems (visual, proprioceptive, and vestibular systems) and the respective weighting of each are needed to maintaining balance during unexpected slip-induced falls. The visual system is often thought of as the most important sensory system in playing a major role in stabilizing posture, guiding locomotion and controlling slip response. However, previous studies have focused on the age-related effects of visual input on static postural stability. The age-related effects of visual input associated with locomotion and unexpected slip perturbations (i.e., dynamic tasks) remains unclear. The purpose of this study is to investigate the age-related effects of visual input on multi-sensory processing during locomotion and unexpected slip perturbations. Fifteen young and fifteen old adults were recruited to participate in this study. Motion capture system, force plate, and EMG data were collected during the experiments. Various biomechanical and neuromuscular characteristics were identified to quantify the age-related effects of visual input during locomotion and unexpected slip perturbations. The results indicate that temporary loss of visual input during walking could cause individuals to adopt a more cautious gait strategy to compensate for their physical and neuronal changes as shown in increased double support time and higher co-contraction (i.e., stiffness) of the knee and ankle joints. Older adults also have higher co-contraction at the ankle joint during walking as compared with young adults. Regarding slip-induced falls, temporary loss of visual input causes increased slip distances and response times of upper and lower limbs in both younger and older groups. In terms of kinematics, the combination of age and temporary loss of visual input influenced the perturbed limb. In terms of muscle activation patterns, temporary loss of visual input may increase the proprioceptive gain as shown in early muscle activity onset, increased muscle activation duration, and increased co-contraction at the knee joint. However, stiffness may increase the difficulty to detect a slip event and reduce flexibility and increase slip-induced falls. Although the human body cannot fully compensate for the temporary loss of visual input, the results in this study suggest that the reweighting process increases proprioceptive gain while visual input is unavailable. These findings support the implication of future research in order to understand the potential hazards which could occur while walking and slipping with temporary loss of visual input. The results may also contribute to the design of effective interventions to improve motor learning by applied visual occlusion in slips/falls training to reduce fall risk and enhance safety. The visual occlusion paradigm may assist to increase learning encoded in intrinsic coordination, related to motor performance skill, providing the flexibility required to adapt to complex environments such as slip-induced falls. / Ph. D.

The objective of the proposed study was to perform three-dimensional (3D) inverse dynamics analysis to determine lower extremity (ankle, knee and hip) joint moments on previously collected slip perturbation experimental data. In addition, the aging effect on the joint moment generation in both normal walking and reactive-recovery conditions was examined. Dataset collected during previous slip and fall experiments, which were conducted in a typical gait analysis setting, were analyzed in current study. All the participants were subjected to the screening criteria, which defined the successful reactive-recovery (i.e. non-fall trials) based on slip distance, sliding heel velocity, whole body COM velocity, and motion pictures. Nine young and nine old healthy participants, who were identified possessing representative trials, were involved as participants in current study. A local coordinate system was constructed on each joint and each segment of the lower extremity based on available landmarks using the Gram-Schmidt orthogonalization algorithm. 3D inverse dynamics was implemented to obtained lower extremity joint moments. Magnitude and timing of obtained joint moment patterns during stance phase were subjected to one and two-way analysis of covariance (ANCOVA) with walking velocity as covariate. The aging effect and gait condition effect were evaluated. Increases in peak joint moment, peak joint power, and joint moment generation ratio were detected in successful reactive-recovery. Distinct age-related joint moment generation strategy was observed through findings of peak joint moment ratio and joint moment generation rate. The elderly, who were able to reactive recover, were found to be as rapid as their younger counterparts in terms of initiating and developing reactive joint moment. It was concluded that ankle joint was critical in balance recovery while hip joint assumed the major responsibility of balance maintenance of upper body during successful reactive-recovery. Increased demand on muscle strength during balance recovery lead to the distinct joint moment generation strategy adopted by the elderly, and confirmed the necessity of lower extremity strength training. In addition, implementation of 3D joint moment analysis was justified in current study and was suggested in future slip and fall researches. / Master of Science

Identifying potential risk factors that affect slip-induced falls is key to developing effective interventions for reduction of injuries caused by these accidents. Existing epidemiological evidence suggests that localized muscle fatigue might be considered as an intrinsic risk factor that causes lack of balance control leading to falls. The literature on the relationship between localized muscular fatigue of the lower extremity and the gait parameters affecting slip severity is scarce. The purpose of the present study was to examine how lower extremity fatigue (quadriceps) alters gait parameters and increases slip severity. Sixteen healthy young participants were recruited to walk across an unexpected slippery floor in two different sessions (Fatigue and No fatigue). Kinematic and kinetic data were collected using a three-dimensional video analysis system and force plates during both sessions. The gait parameters important in assessing slip severity were compared for the two different sessions to evaluate the effects of fatigue. A repeated measure one-way analysis of variance (ANOVA) and multivariate analysis was employed to predict statistical significance. The results indicated a substantial increase in the heel contact velocity (HCV), required coefficient of friction (RCOF), slip distance II (SDII), peak average knee joint moment during slip recovery (kneemompeak), fall frequency and, a decrease in the transitional acceleration of the whole body COM (TA) in the fatigue session further indicating higher slip severity due to fatigue. In addition, a strong positive correlation was observed between RCOF and HCV, HCV and SDII, and, SDII and kneemompeak. These findings provide new insights into the relationship between localized muscular fatigue and slip initiation/recovery process. The present study concluded that localized muscular fatigue affects the gait parameters and increases slip severity and hence can be considered as a potential risk factor for slip-induced falls. / Master of Science

Adults with mental retardation (MR) experience a greater number of falls than their non-disabled peers. To date, efforts to understand the causes for these falls have primarily involved qualitative studies that use largely subjective measures to quantify stability. Performing a more objective biomechanical gait analysis may better explain the reasons for these fall accidents and provide repeatable measures that can be used for comparison to determine the effectiveness of interventions intended to reduce slip-related falls. A gait analysis was conducted to quantify normal walking and slip response characteristics for adults with MR as well as a group of non-disabled age- and gender-matched peers. Kinetic and kinematic data were collected and a number of variables relating to gait pattern, slip propensity, and slip severity were calculated to compare the differences between groups. Results showed that adults with MR exhibit slower walking speeds, shorter step lengths, and greater knee flexion at heel contact suggesting that their gait patterns share more similarities with the elderly than with healthy adults of an equivalent age. Unexpectedly, the MR group demonstrated a lower required coefficient of friction (RCOF) and slower heel contact velocity which, alone, would suggest a reduced slip propensity as compared with the healthy group. A greater peak sliding heel velocity and greater slip distance measures, however, indicate greater slip severity for the MR group. The findings of this study suggest that falls in this population may be attributed to delayed response to slip perturbation as measured by slip distances. / Master of Science