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Jocelyn F. Hafer, Mark S. Miller, Jane A. Kent and Katherine A. Boyer

Older females experience higher rates of disability than males, potentially due to sex-specific differences in gait and muscle function. The authors evaluated the effects of age and physical activity (PA) on gait mechanics and knee extensor muscle function in males and females. Three groups of 20 individuals (each 10 females) participated: young (21–35 y) and highly and less active older (55–70 y) adults. Knee extensor strength and joint mechanics during preferred speed gait were collected before and after 30 minutes of walking. Age by sex and PA by sex interactions indicated older and less active older females had lower concentric knee extensor muscle power and larger hip extension moments than males. After 30 minutes of walking, older less active adults had larger decreases in knee extensor power than their highly active older counterparts, and older adults of both sexes had decreases in ankle dorsiflexion moments while young adults did not. These results suggest that older, particularly less active, adults are susceptible to knee extensor muscle fatigue from moderate activity. For older adults, high levels of PA may be necessary to preserve gait mechanics in response to a bout of exercise. This new information may be important for targeting interventions in at-risk older adults.

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Paula R. Mesquita, Silvia G.R. Neri, Ricardo M. Lima, Eliane F. Manfio and Ana C. de David

Although previous reports have provided normative plantar pressure data for walking in children, evaluation during running is lacking. This study aimed to compare foot loading patterns during running and walking in children aged 4–10 years. Furthermore, the relationship between running baropodometric parameters and anthropometric measures was investigated. Foot loading of 120 volunteers was evaluated during running and walking using an Emed AT-4 pressure platform. Analyses were performed for 5 anatomical regions (rearfoot, midfoot, forefoot, hallux, and lesser toes). Higher peak pressure and maximum force values were seen under most foot regions during running in comparison with walking, whereas relative contact area tended to increase only in the midfoot. Data for running indicated that aging explained less than 23% of the variance of plantar loads and contact area. Running foot loads were more associated with height, body mass, and foot length. This study’s data described plantar loads under the feet of children were greater during running. Aging was associated with little increase in running plantar loads and larger contact areas. Results may be useful as reference to characterize foot loading during running and in the development of orthoses in clinical applications or products such as sport shoes for children.

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Yuko Kuramatsu, Yuji Yamamoto and Shin-Ichi Izumi

This study investigated the sensorimotor strategies for dynamic balance control in individuals with stroke by restricting sensory input that might influence task accomplishment. Sit-to-stand movements were performed with restricted vision by participants with hemiparesis and healthy controls. The authors evaluated the variability in the position of participants’ center of mass and velocity, and the center-of-pressure position, in each orthogonal direction at the lift-off point. When vision was restricted, the variability in the mediolateral center-of-pressure position decreased significantly in individuals with hemiparesis, but not in healthy controls. Participants with hemiparesis adopted strategies that explicitly differed from those used by healthy individuals. Variability may be decreased in the direction that most requires accuracy. Individuals with hemiparesis have been reported to have asymmetrical balance deficits, and that meant they had to prioritize mediolateral motion control to prevent falling. This study suggests that individuals with hemiparesis adopt strategies appropriate to their characteristics.

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Fatemeh Azadinia, Ismail Ebrahimi-Takamjani, Mojtaba Kamyab, Morteza Asgari and Mohamad Parnianpour

The characteristics of postural sway were assessed in quiet standing under three different postural task conditions in 14 patients with nonspecific chronic low back pain and 12 healthy subjects using linear and nonlinear center of pressure parameters. The linear parameters consisted of area, the mean total velocity, sway amplitude, the SD of velocity, and the phase plane portrait. The nonlinear parameters included the Lyapunov exponent, sample entropy, and the correlation dimension. The results showed that the amount of postural sway was higher in the patients with low back pain compared with the healthy subjects. Assessing the nonlinear parameters of the center of pressure showed a lower sample entropy and a higher correlation dimension in the patients with low back pain compared with the healthy subjects. The results of this study demonstrate the greater regularity and higher dimensionality of the center of pressure fluctuations in patients with nonspecific chronic low back pain, which suggests that these patients adopt different postural control strategies to maintain an upright stance.

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Christopher A. DiCesare, Scott Bonnette, Gregory D. Myer and Adam W. Kiefer

Biomechanical analysis can effectively identify factors associated with task performance and injury risk, but often does not account for the interaction among the components that underlie task execution. Uncontrolled manifold (UCM) analyses were applied to data from 38 female, adolescent athletes performing single-leg drop landings and were used to differentiate successful and unsuccessful task performance by examining the frontal plane joint variance within the UCM (V UCM) that stabilized the horizontal center of mass position (V UCM) and within the orthogonal subspace (V ORT). The UCM revealed stronger coordination, indicated by the V UCM/V ORT ratio, in the successful condition. This may inform future research examining reduced motor coordination in failed movement tasks and its relation to injury risk and allow for targeted interventions that consider coordination processes rather than joint-specific outcomes.

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Grace C. Bellinger, Kristen A. Pickett and Andrea H. Mason

Reaching and grasping are often completed while walking, yet the interlimb coordination required for such a combined task is not fully understood. Previous studies have produced contradictory evidence regarding preference for support of the lower limb ipsilateral or contralateral to the upper limb when performing a reaching task. This coordinative aspect of the combined task provides insight into whether the two tasks are mutually modified or if the reach is superimposed upon normal arm swinging. Collectively, 18 right-handed young adults walked slower, took shorter steps, and spent more time in double support during the combined task compared with walking alone. The peak grasp aperture was larger in walking reach-to-grasp trials compared with standing trials. There was not a strong trend for lower limb support preferences at the reach initiation or object contact. The participants could begin walking with either foot and demonstrated variability of preferred gait initiation patterns. There was a range of interlimb coordination patterns, none of which could be generalized to all young adults. The variability with which healthy right-handed young adults execute a combined walking reach-to-grasp task suggests that the cyclical (walking) and discrete (prehension) motor tasks may have separate motor control mechanisms, as proposed in the two primitives theory.

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James Hackney, Jade McFarland, David Smith and Clinton Wallis

Most studies of high-speed lower body movements include practice repetitions for facilitating consistency between the trials. We investigated whether 20 repetitions of drop landing (from a 30.5-cm platform onto a force plate) could improve consistency in maximum ground reaction force, linear lower body stiffness, depth of landing, and jump height in 20 healthy, young adults. Coefficient of variation was the construct for variability used to compare the first to the last five repetitions for each variable. We found that the practice had the greatest effect on maximum ground reaction force (p = .017), and had smaller and similar effects on lower body stiffness and depth of landing (p values = .074 and .044, respectively), and no measurable effect on jump height. These findings suggest that the effect of practice on drop landing differs depending upon the variable measure and that 20 repetitions significantly improve consistency in ground reaction force.

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ZáNean McClain, E. Andrew Pitchford and Jill Pawlowski

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Rafael L. Kons, Kai Krabben, David L. Mann, Gabriela Fischer and Daniele Detanico

In judo competition for visual impairment, athletes of different classes compete against each other in the same category; B1 athletes are totally blind, whereas B2 and B3 athletes are partially sighted. To test for potential competition disparities due a single category of athletes, this study aimed to compare competitive and technical–tactical performance in visually impaired judo athletes with different degrees of visual impairment. The authors analyzed 340 judo matches from the 2012 and 2016 Paralympic Games. The scores, penalties, efficiency index, and types of medals were examined, as well as the technical variation and temporal structure. The main finding was that blind judo athletes presented lower scores (p < .05; effect size [ES] = 0.43–0.73), medals (p < .05), and efficiency (p < .05; ES = 0.40–0.73); different patterns of play; and a shorter time to lose than partially sighted athletes (p = .027; ES = 0.10–0.14). However, the penalties were similar between classes (p > .05; ES = 0.07–0.14). The odds ratio of a winning medal was 3.5–8 times less in blind athletes than in partially sighted athletes (p < .01). In conclusion, blind judo athletes presented lower competitive and technical–tactical performance than athletes with some residual functional vision. These findings provide support for the development of new evidence-based criteria for judo classification based on vision impairment.

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Rachael C. Stone, Shane N. Sweet, Marie-Josée Perrier, Tara MacDonald, Kathleen A. Martin Ginis and Amy E. Latimer-Cheung

Identifying as a regular exerciser has been found to effectively alter stereotypes related to warmth and competence for adults with a physical disability; however, it remains unclear how sport participation can influence this trend. Therefore, this study aimed to examine warmth and competence perceptions of adults with a physical disability portrayed as elite and nonelite athletes relative to other athletic and nonathletic subgroups of adults with and without a physical disability in the context of the stereotype content model. Using survey data from able-bodied participants (N = 302), cluster analyses were applied to a behaviors from intergroup affect and stereotypes map for displaying the intersection of warmth and competence perceptions. The results demonstrated that adults with a physical disability who are described as elite athletes (i.e., Paralympians) are clustered with high warmth and high competence, similar to their able-bodied athletic counterparts (i.e., Olympians). The findings suggest that perceiving athletic and elite sport statuses for adults with a physical disability may counter the stereotypes commonly applied to this group.