The maladaptive effects of work-related strain constitute an ongoing and growing problem for many workers in the modern workplace. Contemporary understanding of the physiology of brain arousal processes suggests a consistent balance between brain arousal and recovery over the 24-hour work/rest cycle is crucial for maintaining an adaptative response to work strain. Broadly, intense brain arousal tends to occur at work, whilst its recovery occurs in non-work time, usually at home. This thesis describes the development and validation of a new self-report measure of work-related strain, which incorporates a new and unique measurement of recovery from work strain between successive work periods. This instrument has facilitated several studies of recovery from work-related stress/fatigue, which are reported in the form of papers published, in press or in review with peer-reviewed journals. In particular, it is evident that the type and frequency of non-work time behaviour may be significant in determining the level of recovery from acute work strain. This, in turn, mediates the quality of sleep subsequently achieved, and these combine synergistically to determine overall level of recovery that is achieved between work periods. Consistent with the known physiology of brain arousal and recovery, which is described, non-work time behaviours, which mediate adequate recovery from work strain consistently, may represent the difference between long-term adaptative and maladaptive outcomes of work strain exposure. This suggests an area for work-stress intervention hitherto underestimated in fatigue/stress research. It is argued to be of significance for workers in high stress occupations, since non-work time behaviour is potentially more completely within their discretionary power, than the stress/fatigue levels to which they may be regularly exposed through the inherent nature of their work.

Slips, trips, and falls are a serious public health concern, particularly among older adults and within occupational settings, given that falls contribute to a large number of injuries and associate with high medical costs. To reduce the number of falls, there is a need to better understand risk factors contributing to falls, and to develop and evaluate improved balance training interventions to prevent falls. To address these needs, this work has two primary goals: first, to better understand risk factors contributing to falls, including fatigue and balance reactions after a large postural perturbation, and, second, to develop and evaluate improved reactive balance training (RBT) interventions to reduce risk of falls due to slipping and tripping. The first study investigated the effects of performing occupationally-relevant fatigue-inducing physical work on trip and fall risk. Healthy young adults performed a simulated manual material handling (MMH) task, using either heavy or light boxes, for two hours. Gait measures related to risk of tripping and slipping were assessed before and after the task. Reactive balance during one laboratory-induced trip was also assessed after the task. Results showed that performing the heavy MMH task did not affect risk of tripping or slipping, or reactive balance after tripping. These results may have resulted from insufficient fatigue due to the MMH task. The second study investigated the relationship between feet kinematics upon slipping while walking, and the outcome of the slip. Seventy-one laboratory-induced slips were analyzed, which included recoveries, feet-split falls, feet-forward falls, and lateral falls. Feet kinematics differed between these four slip outcomes, and a discriminant model including six measures of feet kinematics correctly predicted 87% of slip outcomes. Two potentially modifiable characteristics of feet kinematics upon slipping that can improve the likelihood of successfully averting a fall were identified: (1) quickly arresting the motion of the slipping foot; and (2) a recovery step that places the trailing toe approximately 0-10% body height anterior to the sacrum. This information may be used to guide the development of improved RBT interventions to reduce risk of slip-induced falls. The third study evaluated the efficacy of two low-cost, low-tech RBT methods for improving reactive balance after slipping. The two methods were: unexpected slip training (UST), which involved repeated unexpected slips while walking and volitional slip-recovery training (VST), which involved practicing balance reactions after volitionally inducing a slip-like perturbation. Young adults completed one session of an assigned intervention (UST, VST, or control), followed by one unexpected, laboratory-induced slip while walking. Compared to controls, UST and VST resulted in a higher proportion of successful balance recoveries from the laboratory-induced slips. UST improved both proactive control and reactive stepping after slipping, while VST primarily improved the ability to arrest slipping foot motion. These results support the use of UST and VST as practical, low-tech methods of slip training. The fourth study evaluated the efficacy of RBT that targets both slipping and tripping. Community-dwelling, healthy older adults (61-75 years) completed four sessions of either RBT (treadmill-based trip-recovery training and VST) or control training (general strength and balance exercises). Reactive balance during unexpected laboratory-induced slips and trips was assessed before and after RBT, and compared between subjects at baseline (before the intervention), after control training, and after RBT. The incidence of slip-induced falls differed between groups in that 80% fell at baseline, 60% fell after control training, and 18% fell after RBT. Post-RBT subjects also exhibited less severe slips, compared to baseline and post-control subjects. The incidence of trip-induced falls did not differ between groups, but margin of stability after tripping was greater for post-RBT subjects, compared to post-control subjects. These results show promise for the use of RBT applied to both slipping and tripping to reduce fall risk among older adults. / Doctor of Philosophy / Slips, trips, and falls are a serious public health concern, given that falls contribute to a large number of injuries and deaths. Falls are particularly concerning among older adults, who are reported to fall more frequently, and within occupational settings, where falls cause a larger number of injuries and a significant economic burden. To reduce the number of falls, there is a need to better understand risk factors contributing to falls, and to develop and evaluate improved balance training interventions to prevent falls. Four studies were conducted to address these needs: two studies aimed to better understand risk factors contributing to falls, including fatigue and balance reactions after slipping, and two studies aimed to develop and evaluate improved balance training interventions to reduce risk of falls due to slipping and tripping. This work focused on slipping and tripping, because slips and trips are reported to cause a large number of injuries and falls among both workers and older adults. The first study investigated the effect of performing occupationally-relevant fatigue-inducing physical work on trip and fall risk among healthy young adults, and results showed that performing a simulated manual material handling task (i.e. moving and stacking boxes using a two-wheeled dolly) did not affect risk of tripping and falling. The second study investigated the relationship between balance reactions after slipping and the outcome of the slip. Results showed that balance reactions of the feet predicted the outcome of the slip (i.e. recovering balance or one of three types of slip-induced falls) with 87% accuracy. We also identified characteristics of balance reactions that can improve the likelihood of successfully averting a fall. The third study evaluated the efficacy of two low-tech reactive balance training (RBT) methods for reducing slip-induced fall risk among young adults. These methods involved practicing balance reactions after slip-like perturbations, induced either unexpectedly or volitionally. Results showed that both RBT methods improved reactive balance after slipping, but through different mechanisms. The fourth study evaluated the efficacy of a RBT intervention targeting both slipping and tripping among older adults. Results showed that RBT improved reactive balance during both slipping and tripping, and reduced the incidence of slip-induced falls. In conclusion, these results help to better understand risk factors contributing to falls, and support the use of practical reactive balance training interventions targeting both slipping and tripping to reduce fall risk.

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