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Leah S. Goudy, Brandon Rhett Rigby, Lisa Silliman-French and Kevin A. Becker

The purpose of this study was to determine changes in balance, postural sway, and quality of life after 6 wk of simulated horseback riding in adults diagnosed with Parkinson’s disease. Eight older adults completed two 60-min riding sessions weekly for 6 wk. Variables of balance, postural sway, and quality of life were measured 6 wks before and within 1 wk before and after the intervention. Berg Balance Scale scores decreased from baseline to preintervention (48.36 ± 5.97 vs. 45.86 ± 6.42, p = .050) and increased from preintervention to postintervention (45.86 ± 6.42 vs. 50.00 ± 4.38, p = .002). Cognitive impairment, a dimension of quality of life, improved from baseline to postintervention (37.5 ± 20.5 vs. 21.5 ± 14.4, p = .007). Six weeks of simulated horseback riding may improve balance and cognitive impairment in older adults with Parkinson’s disease.

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Mhairi K. MacLean and Daniel P. Ferris

The authors tested 4 young healthy subjects walking with a powered knee exoskeleton to determine if it could reduce the metabolic cost of locomotion. Subjects walked with a backpack loaded and unloaded, on a treadmill with inclinations of 0° and 15°, and outdoors with varied natural terrain. Participants walked at a self-selected speed (average 1.0 m/s) for all conditions, except incline treadmill walking (average 0.5 m/s). The authors hypothesized that the knee exoskeleton would reduce the metabolic cost of walking uphill and with a load compared with walking without the exoskeleton. The knee exoskeleton reduced metabolic cost by 4.2% in the 15° incline with the backpack load. All other conditions had an increase in metabolic cost when using the knee exoskeleton compared with not using the exoskeleton. There was more variation in metabolic cost over the outdoor walking course with the knee exoskeleton than without it. Our findings indicate that powered assistance at the knee is more likely to decrease the metabolic cost of walking in uphill conditions and during loaded walking rather than in level conditions without a backpack load. Differences in positive mechanical work demand at the knee for varying conditions may explain the differences in metabolic benefit from the exoskeleton.

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Amy R. Lewis, William S.P. Robertson, Elissa J. Phillips, Paul N. Grimshaw and Marc Portus

For the wheelchair racing population, it is uncertain whether musculoskeletal models using the maximum isometric force-generating capacity of nonathletic, able-bodied individuals are appropriate, as few anthropometric parameters for wheelchair athletes are reported in the literature. In this study, a sensitivity analysis was performed in OpenSim, whereby the maximum isometric force-generating capacity of muscles was adjusted in 25% increments to literature-defined values between scaling factors of 0.25x and 4.0x for 2 elite athletes, at 3 speeds representative of race conditions. Convergence of the solution was used to assess the results. Artificially weakening a model presented unrealistic values, while artificially strengthening a model excessively (4.0x) demonstrated physiologically invalid muscle force values. The ideal scaling factors were 1.5x and 1.75x for each of the athletes, respectively, as was assessed through convergence of the solution. This was similar to the relative difference in limb masses between dual-energy X-Ray absorptiometry data and anthropometric data in the literature (1.49x and 1.70x), suggesting that dual-energy X-ray absorptiometry may be used to estimate the required scaling factors. The reliability of simulations for elite wheelchair racing athletes can be improved by appropriately increasing the maximum isometric force-generating capacity of muscles.

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James W. Roberts

Investigations of visually guided target-directed movement frequently adopt measures of within-participant spatial variability to infer the contribution of planning and control. The present study aims to verify this current trend by exploring the distribution of displacements at kinematic landmarks with a view to understand the potential sources of variability. Separate sets of participants aiming under full visual feedback conditions revealed a comparatively normal distribution for the displacements at peak velocity and movement end. However, there was demonstrable positive skew in the displacement at peak acceleration and a significant negative skew at peak deceleration. The ranges of the distributions as defined by either ±1SD or ±34.13th percentile (equivalent to an estimated 68.26% of responses) also revealed differences at peak deceleration. These findings indicate that spatial variability in the acceleration domain features highly informative systematic, as well as merely inherent, sources of variability. Implications for the further quantification of trial-by-trial behavior are discussed.

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Etem Curuk, Yunju Lee and Alexander S. Aruin

The authors investigated anticipatory postural adjustments in persons with unilateral stroke using external perturbations. Nine individuals with stroke and five control subjects participated. The electromyographic activity of 16 leg and trunk muscles was recorded. The onsets of muscle activity during the anticipatory phase of postural control were analyzed. The individuals with stroke did not show an anticipatory activation of leg and trunk muscles on the affected side; instead, the muscle onsets were seen after the perturbation, during the balance restoration phase. However, an anticipatory activation of muscles on the unaffected side was seen in individuals with stroke, and it was observed earlier compared with healthy controls (p < .05). The individuals with stroke showed a distal to proximal order of anticipatory activation of muscles on the unaffected side. The outcome of the study provides a basis for future investigations regarding ways of improving balance control in people with stroke.

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Eric Foch and Clare E. Milner

It is unknown if female runners who have sustained multiple iliotibial band syndrome occurrences run differently compared with runners who developed the injury once or controls. Therefore, the purpose of this study was to determine if differences existed in coordination patterns and coordination variability among female runners with recurrent iliotibial band syndrome, 1 iliotibial band syndrome occurrence, and controls. Overground running trials were collected for 36 female runners (n = 18 controls). Lower extremity coordination patterns were examined during running via a vector coding analysis. Coordination variability was calculated via the ellipse area method. Separate 1-way (group) Kruskal–Wallis tests were performed to compare each coordination pattern and coordination variability. Lower extremity coordination between frontal plane hip–transverse plane hip, frontal plane pelvis–frontal plane thigh, and frontal plane thigh–transverse plane shank was similar among groups and so may not be related to the risk of iliotibial band syndrome. Runners with 1 iliotibial band syndrome occurrence demonstrated greater coordination variability for 2 of 3 couplings compared with both controls and runners with recurrent iliotibial band syndrome. Thus, the number of previous injury episodes may influence coordination variability in female runners with a history of iliotibial band syndrome.

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Ljudmila Zaletelj

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Danny M. Pincivero, Rachael R. Polen and Brittany N. Byrd

The objective of the present study was to examine the relationship between maximal effort force production and anthropometric measures of upper-arm volume. Thirty healthy young participants (15 women) performed 5 isokinetic concentric and eccentric maximal effort elbow flexor/extensor contractions on separate days. Measures of arm length, circumference, and skinfold/subcutaneous fat thickness were used to obtain a measure of arm volume, modeled as 2 separate right-angle frustra. Single-variable regression analyses demonstrated significant (P < .001) second-order polynomial relationships between maximal effort elbow flexor and extensor force with arm volume (r 2 = .63–.86). The major findings demonstrated that strong and positive relations between maximal force production and estimates of limb volume can be observed using nonlinear modeling and a closer geometric representation of the exercising limb.

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Xihe Zhu and Justin A. Haegele

The purpose of this study was to examine reactivity to accelerometer measurement in children with visual impairments (VI), their sighted siblings, and their parents. A sample of 66 participants (including 22 children with VI, 22 siblings, and 22 parents) completed a demographic survey and wore triaxial accelerometers for at least 4 consecutive days for 8 hr. An analysis of covariances with repeated measures was conducted, controlling for participant gender. Children with VI had 8.1% less moderate to vigorous physical activity time on Day 1 than Days 2–4 average. Their sighted siblings and parents had 7.8% and 7.1% more moderate to vigorous physical activity time on Day 1 than their Days 2–4 average, respectively. The reactivity percentage for parents and children without VI is consistent with existing literature. However, an inverse reactivity for children with VI was found, which is a unique contribution to the literature and will have implications for researchers using accelerometers for this population.

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Kevin Deschamps, Giovanni Matricali, Maarten Eerdekens, Sander Wuite, Alberto Leardini and Filip Staes

Foot structure and kinematics have long been considered as risk factors for foot and lower-limb running injuries. The authors aimed at investigating foot joint kinetics to unravel their receptive and propulsive characteristics while running barefoot, both with rearfoot and with midfoot striking strategies. Power absorption and generation occurring at different joints of the foot in 6 asymptomatic adults were calculated using both a 3-segment and a 4-segment kinetic model. An inverse dynamic approach was used to quantify mechanical power. Major power absorption and generation characteristics were observed at the ankle joint complex as well as at the Chopart joint in both the rearfoot and the midfoot striking strategies. The power at the Lisfranc joint, quantified by the 4-segment kinetic model, was predominantly generated in both strategies, and at the toes, it was absorbed. The overall results show a large variability in the receptive and propulsive characteristics among the analyzed joints in both striking strategies. The present study may provide novel insight for clinical decision making to address foot and lower-limb injuries and to guide athletes in the adoption of different striking strategies during running.