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Falls and fall-induced injuries are common and consequential in older adults. Ballet emphasizes full-body coordination, leg strength, and postural control. However, it remains unknown if ballet can indeed reduce falls in older adults. This study examined biomechanical and neuromuscular responses of older recreational ballet dancers to an unexpected standing-slip. Twenty older ballet dancers (17 females, 3 males) and 23 age- and sex-matched non-dancers (19 females, 4 males) were exposed to an unexpected slip during treadmill standing. The slip-faller rate was the primary outcome. The secondary outcomes were kinematic measurements, including dynamic gait stability, slip distance, and recovery stepping performance (step latency, duration, length, and speed). The tertiary outcome was the electromyography latency of leg muscles (bilateral tibialis anterior, medial gastrocnemius, rectus femoris, and biceps femoris). Fewer dancers fell than non-dancers after the standing-slip (45% vs. 83%, p=0.005, d=0.970). Dancers displayed better stability at recovery foot liftoff (p=0.006) and touchdown (p=0.012), a shorter step latency (p=0.020), shorter step duration (p=0.011), faster step speed (p=0.032), and shorter slip distance (p=0.015) than non-dancers. They exhibited shorter latencies than non-dancers for the standing leg rectus femoris (p=0.028) and tibialis anterior (p=0.002), and the stepping leg biceps femoris (p=0.031), tibialis anterior (p=0.017), and medial gastrocnemius (p=0.030). The results suggest that older ballet dancers experience a lower fall risk and are more stable than non-dancers following an unexpected standing-slip. The greater stability among dancers could be attributed to more biomechanically effective recovery stepping, possibly associated with the ballet-induced neuromuscular benefit - an earlier leg muscle activation.

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It is well recognized that overall obesity increases fall risk. However, it remains unknown if the obesity-induced increase in the fall risk depends upon the adipose distribution (or obesity type: android vs. gynoid). This pilot study examined the effects of fat deposition region on fall risk following a standing-slip trial in young adults with simulated android or gynoid adiposity. Appropriate external weights were attached to two groups of healthy young lean adults at either the abdomen or upper thigh region to simulate android or gynoid adiposity, respectively, with a targeted body mass index of 32 kg/m2. Under the protection of a safety harness, both groups were exposed to an identical standing-slip on a treadmill with a maximum slip distance of 0.36 m. The primary (dynamic gait stability) and secondary (latency, length, duration, and speed of the recovery step, slip distance, and trunk velocity) outcome variables on the slip trial were compared between groups. The results revealed that the android group was more unstable with a longer slip distance and a slower trunk flexion velocity than the gynoid group at the recovery foot liftoff after the slip onset. The android group initiated the recovery step later but executed the step faster than the gynoid group. Biomechanically, the android adipose tissue may be associated with a higher fall risk than the gynoid fat tissue. Our findings could provide preliminary evidence for considering fat distribution as an additional fall risk factor to identify older adults with obesity at a high fall risk.

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Ballet training is being increasingly used to improve physical functions in older adults. Our previous work showed that ballet dancers react to a novel standing-slip more effectively than their non-dancer counterparts through better control of the recovery step and trunk movement. The purpose of this study was to test if and to what extent ballet dancers adapt differently to repeated standing-slips relative to non-dancers. Protected by a harness, twenty young adults (10 professional ballet dancers and 10 age/sex-matched non-dancers) experienced five repeated and standardized standing-slips on a treadmill. Changes from the first slip (S1) to the fifth slip (S5) in dynamic gait stability (primary outcome) and other variables, including the center of mass position and velocity, step latency, slip distance, ankle angle, and trunk angle (secondary outcomes) were compared between groups. Results revealed that both groups adopted similar proactive controls to improve dynamic gait stability by using the ankle and hip strategies. However, dancers showed a better reactive improvement in stability after the repeated slips than non-dancers. From S1 to S5, dancers reactively improved their dynamic gait stability more than non-dancers at the recovery step liftoff (p = 0.003). Dancers decreased their recovery step latency (p = 0.004) and shortened the slip distance (p = 0.004) significantly more than non-dancers from S1 to S5. These findings suggest that ballet dancers could facilitate the adaptation to repeated slips, which may be attributed to their ballet practice experience. This finding augments our understanding of the underlying mechanisms of ballet practice reducing falls.

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Although interventional studies have suggested that dance-based training may reduce fall risk for older adults based on unperturbed assessments, it remains unknown whether dance (particularly ballet) enhances recovery from an external perturbation. This preliminary study sought to test if and how ballet dancers respond differently to a novel standing-slip perturbation relative to non-dancers. Ten young professional ballet dancers and 10 age/sex-matched non-dancers were exposed to an unannounced slip while standing on the treadmill. Their reactions to the slip, characterized by dynamic gait stability (primary outcome), and the recovery stepping and trunk movements (secondary outcomes), were compared between groups. No significant group difference in dynamic gait stability was found at slip onset and recovery step liftoff, but dancers were more stable than non-dancers at touchdown (p = 0.046). Compared to non-dancers, dancers took a longer (p = 0.049) and faster (p = 0.007) backward recovery step and exhibited a less backward leaned trunk at all instants (p ≤ 0.026). Our study suggests that professional ballet dancers are more stable after a novel standing-slip than non-dancers. This better slip-related fall resistance among dancers could result from their more effective recovery stepping strategy and better trunk movement control after the slip. Both reactions may be attributed to ballet training, which requires frequent backward stepping and an upright trunk. Our findings could potentially provide preliminary evidence for applying ballet training to reduce balance losses and falls in people at a high fall risk. More studies are needed to examine ballet training's effects among other populations with elevated fall risk in real-life situations.

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Adults with obesity have gait instability, leading to increased fall risks and decreased physical activity. Whole-body angular momentum (WBAM) is regulated over a gait cycle, essential to avoid a fall. However, how obese adults regulate WBAM during walking is unknown. The current study investigated changes in WBAM about the body's center of mass (COM) during walking in obese and non-obese adults across different walking speeds. Twenty-eight young adults with obesity and normal weight walked barefoot at a fixed walking speed (FWS, 1.25 m/s) and at five different speeds based on their preferred walking speed (PWS): 50, 75, 100, 125, and 150 % of PWS. Adults with obesity walked slower with shorter step length, wider step width, and longer double support time (p < 0.01). The ranges of frontal- and transverse-plane WBAM were greater in obese adults (p < 0.01). We also found that the range of frontal-plane WBAM did not significantly change with walking speed (p > 0.05), while the range of transverse-plane WBAM increased with walking speed (p < 0.01). The ranges of frontal- and transverse-plane WBAM increased with the mediolateral ground reaction force and mediolateral moment arm (p < 0.01), which may be most affected by lateral foot placement relative to the body's COM. Our findings suggest that controlling mediolateral stability during walking is more challenging in obese adults, independent of their slow walking speed. Understanding whole-body rotational dynamics observed in obese walking provides an insight into the biomechanical link between obesity and gait instability, which may help find a way to reduce fall risks and increase physical activity.

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Anterior load carriage, identified as a fall risk factor, is commonly required in daily living activities and occupations. Dynamic gait stability quantifies the kinematic relationship between the human body's center of mass and base of support and has been widely used to assess fall risk. The current study was conducted as a portion of a larger project exploring the effects of anterior load carriage on the control of body stability during various walking conditions. Particularly, this study examined the effect of anterior load carriage on dynamic gait stability during level overground walking among young adults. It was hypothesized that anterior load carriage would compromise dynamic gait stability during walking. Thirty young adults were evenly randomized into three groups: no load (Group 1), 10% body mass (bm) (Group 2), and 20% bm (Group 3). Each group walked overground at a self-selected speed carrying the assigned load. Kinematics were collected for the body and load through motion capture. Dynamic gait stability, gait speed, step length, and trunk angle were determined based on the kinematics and compared between groups. The results did not detect significant load-related effects on dynamic gait stability, step length, or gait speed. A significant load-related difference was found in trunk angle: the heavier the load, the more backward leaned trunk. Further analyses revealed a more posteriorly-leaned trunk in Groups 2 and 3 than Group 1 and in Group 3 than Group 2. The results indicated that young adults could maintain dynamic gait stability when carrying a front load by leaning the trunk backward but keeping other gait parameters unchanged.

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BACKGROUND: Anteriorly-loaded walking is common in many occupations and may increase fall risk. Dynamic gait stability, defined by the Feasible Stability Region (FSR) theory, quantifies the kinematic relationship between the body's center of mass (COM) and base of support (BOS). FSR-based dynamic gait stability has been used to evaluate the fall risk. RESEARCH QUESTION: How does front load carriage affect dynamic gait stability, step length, and trunk angle among young adults during treadmill walking? METHODS: In this between-subject design study, 30 healthy young adults were evenly randomized into three load groups (0%, 10%, or 20% of body weight). Participants carried their assigned load while walking on a treadmill at a speed of 1.2 m/s. Body kinematics were collected during treadmill walking. Dynamic gait stability (the primary variable) was calculated for two gait events: touchdown and liftoff. Step length and trunk angle were measured as secondary variables. One-way analysis of variance was conducted to detect any group-related differences for all variables. Post-hoc analysis with Bonferroni correction was performed when main group differences were found. RESULTS: No significant differences but medium to large effect sizes were found between groups for dynamic gait stability at touchdown (p = 0.194, η2 = 0.114) and liftoff (p = 0.122, η2 = 0.139). Trunk angle significantly increased (indicating backward lean) with the front load at touchdown (p < 0.001, η2 = 0.648) and liftoff (p < 0.001, η2 = 0.543). No significant between-group difference was found related to the step length (p = 0.344, η2 = 0.076). SIGNIFICANCE: Carrying a front load during walking significantly alters the trunk orientation and may change the COM-BOS kinematic relationship and, therefore, fall risk. The findings could inform the design of future studies focusing on the impact of anterior load carriage on fall risk during different locomotion.

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Tai-Chi (TC) practice has been increasingly used to prevent falls in older adults. However, the biomechanical mechanisms underlying the effects of TC practice on fall risk among older adults remain unanswered. The objective of this pilot study was to examine how TC gait biomechanically impacts the human body in terms of dynamic gait stability and lower limb muscle strength in comparison with regular walking gait. Ten healthy adults performed five trials of TC gait following three to seven trials of regular walking. Full body kinematics and kinetics were collected, and then dynamic gait stability and lower limb joint moments were determined. During TC gait, individuals were less stable, moved more slowly and experienced a larger mediolateral movement in comparison with regular walking gait. The peak moment at the ankle joint on the sagittal and transverse planes, at the knee joint on all three planes, and at the hip joint on the frontal plane was significantly different when performing TC gait than during regular gait. The results indicate that TC gait challenges body balance and requires more muscle strength of the lower limb joints compared to regular walking gait. To cope with these challenges, the body could develop neuromuscular control strategies to maintain body balance and thus reduce the risk of falls. The findings and methodology in this study could provide preliminary guidance for identifying optimal TC forms in order to maximize the effects of TC-based fall prevention interventions among various populations with elevated risk of falls.

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BACKGROUND: Perturbation training, built upon motor adaptation and learning, has been increasingly used as a fall prevention paradigm in older adults. This training paradigm involves repeated externally-induced perturbations (like slips) to facilitate the error-driven learning of necessary motor skills for preventing falls. It remains unknown if people with multiple sclerosis can adapt to large-scale slip perturbations, which impedes the application of perturbation training in persons with multiple sclerosis. This study explored whether people with multiple sclerosis can adapt to large-scale repeated gait-slips. METHODS: Thirteen individuals with multiple sclerosis (the mean ± standard deviation of the Patient Determined Disability Steps: 2.27 ± 1.42) were exposed unexpectedly to a block of five repeated standard slips while walking on a treadmill. The outcome (fall or recovery) for each slip, as our primary outcome measure, was determined. A battery of secondary variables, including dynamic gait stability and gait parameters, were also calculated. Both primary and secondary variables were compared across trials. RESULTS: Our participants showed a rapidly reduced slip-fall rate (from 92.3% on the first slip to 30.8% on the fifth, p < 0.001). They mainly adopted proactive, assisted by reactive, strategies to improve dynamic gait stability, thus reducing the risk of slip-falls. The proactive adjustments, including shortened step, reduced foot landing angle, and flexed knee, shifted the center of mass anteriorly to be closer to the base of support. Such changes in center of mass position improved dynamic gait stability before the slip. Dynamic gait stability after the slip was also improved across trials, as a reactive strategy. CONCLUSION: With practice, people with multiple sclerosis can adapt to large-scale, high-speed, gait-slips and acquire necessary skills against falls. Such skills primarily involve proactive strategy which is assisted by reactive strategy. The proactive strategy would shift the body's center of mass closer to the base of support, improving dynamic gait stability and reducing falls. Our findings could provide a theoretical foundation for deploying perturbation training to prevent falls in people with multiple sclerosis.

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BACKGROUND: While the effects of diseases, performance of proprioceptors, anxiety or pain on gait stability or automaticity of walking are well-explored, physical fatigue might be another relevant factor whose consequences are not sufficiently investigated, yet. RESEARCH QUESTION: The aim of the current study was to evaluate the effect of physical exhaustion on local dynamic stability (LDS) and automaticity of gait. METHODS: In a randomized controlled trial, 30 young and healthy adults were randomly assigned to either a passive control group or a fatigue group. The participants assigned to the fatigue group passed a shuttle-run test which finished at maximal exhaustion while those of the control group rested in sitting position for 15 min. Immediately before and after the intervention, local dynamic gait stability as well as the cognitive (serial seven subtractions) and motor dual-task costs, as a measure of automaticity, were registered. RESULTS: While there was no effect of fatigue on LDS during single-task walking, we observed an interaction effect for LDS in the dual-task condition (p = .034) and for the motor dual-task costs (p = .031). Lower dual-task costs were found in the fatigued group in the post-test compared to the pre-test while the control group increased their costs at the same time. SIGNIFICANCE: In conclusion, gait automaticity might increase after total exhaustion in young adults. Still, the underlying mechanisms are not completely resolved and further research incorporating measurements of cortical gait control might be promising.

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Posturography is used to assess balance in clinical settings, but its relationship to gait stability is unclear. We assessed if dynamic gait stability is associated with standing balance in 12 patients with unilateral vestibulopathy. Participants were unexpectedly tripped during treadmill walking and the change in the margin of stability (MoSchange) and base of support (BoSchange) relative to nonperturbed walking was calculated for the perturbed and first recovery steps. The center of pressure (COP) path during 30-s stance with eyes open and closed, and the distance between the most anterior point of the COP and the anterior BoS boundary during forward leaning (ADist), were assessed using a force plate. Pearson correlations were conducted between the static and dynamic variables. The perturbation caused a large decrease in the BoS, leading to a decrease in MoS. One of 12 correlations was significant (MoSchange at the perturbed step and ADist; r = -.595, P = .041; nonsignificant correlations: .068 ≤ P ≤ .995). The results suggest that different control mechanisms may be involved in stance and gait stability, as a consistent relationship was not found. Therefore, posturography may be of limited use in predicting stability in dynamic situations.

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The aim of this work was to examine locomotor stability and adaptation across the adult female lifespan during perturbed walking on the treadmill. 11 young, 11 middle and 14 older-aged female adults (mean and SD: 25.5(2.1), 50.6(6.4) and 69.0(4.7) years old respectively) walked on a treadmill. We applied a sustained perturbation to the swing phase of the right leg for 18 consecutive gait cycles, followed by a step with the resistance unexpectedly removed, via an ankle strap connected to a break-and-release system. The margin of stability (MoS) at foot touchdown was calculated as the difference between the anterior boundary of the base of support (BoS) and extrapolated center of mass. Older participants showed lower MoS adaptation magnitude in the early adaptation phase (steps 1-3) compared to the young and middle-aged groups. However, in the late adaptation phase (steps 16-18) there were no significant differences in adaptation magnitude between the three age groups. After removing the resistance, all three age groups showed similar aftereffects (i.e. increased BoS). The current results suggest that in old age, the ability to recalibrate locomotion to control stability is preserved, but the rate of adaptive improvement in locomotor stability is diminished.

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