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Brock Laschowski, Naser Mehrabi and John McPhee

wheelchair curling. These investigations would provide unprecedented insights into the physical demands of this Paralympic sport. One of the main objectives of biomechanists is to evaluate the dynamics (ie, forces and moments) associated with human movements. Experimentally measuring the forces of individual

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Scott W. Ducharme and Richard E.A. van Emmerik

related to aging and disease. In the second section, we provide an overview of past and current research on coordination dynamics that demonstrates the functional role of variability in human locomotion. Next, the major section of this paper addresses the concept of fractals that has provided new insights

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Eric G. James

The HKB model and its variants characterize bimanual coordination with fixedpoint dynamics and predict stationarity of the mean and variance of relative phase in stable coordinative states. In the current study, participants performed in-phase and antiphase coordination modes in rhythmic bimanual finger and elbow flexionextension tasks. The results of runs tests revealed that discrete relative phase was nonstationary in 49.25%, 50.25%, and 54% of time-series in the 10, 20, and 30 box runs tests, respectively. In all individual Task conditions >38% of time-series were nonstationary. These findings contradicted model predictions that the mean and variance of relative phase are stationary in bimanual coordination and distinguish the concept of dynamical stability from statistical stationarity. The findings indicated that relative phase was not attracted to a stationary fixed-point and that fluctuations in relative phase are not Gaussian white noise as in existing models of bimanual coordination.

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Stacy M. Lopresti-Goodman, Michael J. Richardson, Reuben M. Baron, Claudia Carello and Kerry L. Marsh

The actualization of a simple affordance task—grasping and moving wooden planks of different sizes using either one or two hands—was assessed in the context of taskrelevant (plank sequence, plank presentation speed) and task-irrelevant (cognitive load) manipulations. In Experiment 1, fast (3 s/plank) and self-paced (≈5 s/plank) presentation speeds revealed hysteresis; the transition point for ascending series was greater than the transition point for descending series. Hysteresis was eliminated in the slowest presentation speed (10 s/plank). In Experiment 2, hysteresis was exaggerated by a cognitive load (counting backward by seven) for both fast and slow presentation speeds. These results suggest that behavioral responses to the attractor dynamics of perceived affordances are processes that require minimal cognitive resources.

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Christopher K. Rhea and Matthew W. Wittstein

Much has been learned about the characteristics of gait in overground and treadmill walking. However, there are many contexts in which overground or treadmill walking might not be possible, such as in home-based physical therapy. In those cases, a surrogate task to index gait behavior would be a valuable tool. Thus, the purpose of this study was to evaluate the stride behavior characteristics of stationary stepping compared with treadmill walking. Healthy young adults (N = 10) preformed two 15-minute tasks: (1) treadmill walking and (2) stationary stepping. Several stride behavior characteristics were recorded, including the number of strides taken, minimum and maximum knee angle, stride interval mean, stride interval standard deviation, and detrended fluctuation analysis (DFA) alpha of the stride interval time series. The results showed that stride behavior was similar between tasks when examined at the group level. However, when individual level analyses were used to examine the reliability of each metric between tasks, poor reliability was observed in most metrics, indicating that stationary stepping may not be an appropriate surrogate task for overground or treadmill walking. These results are discussed in the context of a gait dynamics framework, with attention to task constraints that may have influenced the findings.

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Heather J. Leach, Katie B. Potter and Mary C. Hidde

when theory-based PA behavior change strategies are combined with group dynamics strategies targeting group processes, structure, and environment (see Table  1 for examples of these strategies). 22 – 24 Group dynamics is a field of study that examines the positive and negative forces that reside

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Brennan Petersen, Mark Eys, Kody Watson and M. Blair Evans

physical activity motivation in sport programs ( Côté, Turnnidge, & Evans, 2014 ). Given the prevalence of group contexts in sport and the importance of the social environment for motivating youth 1 participants, understanding and enhancing group dynamics is critical to facilitate youths’ participation in

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Paul J. Makhoul, Kathryn E. Sinden, Renée S. MacPhee and Steven L. Fischer

Paramedics represent a unique occupational group where the nature of their work, providing prehospital emergency care, makes workplace modifications to manage and control injury risks difficult. Therefore, the provision of workplace education and training to support safe lifting remains a viable and important approach. There is, however, a lack of evidence describing movement strategies that may be optimal for paramedic work. The purpose of this study was to determine if a strategy leveraging a greater contribution of work from the lower body relative to the torso was associated with lower biomechanical exposures on the spine. Twenty-five active duty paramedics performed 3 simulated lifting activities common to paramedic work. Ground reaction forces and whole body kinematics were recorded to calculate: peak spine moment and angle about the L4/L5 flexion-extension axis as indicators of biomechanical exposure; and, joint work, integrated from net joint power as a measure of technique inclusive of movement dynamics. Paramedics generating more work from the lower body, relative to the trunk, were more likely to experience lower peak L4/L5 spine moments and angles. These data can inform the development of workplace training and education on safe lifting that focuses on paramedics generating more work from the lower body.

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Rachel A. Van Woezik, Alex J. Benson and Mark W. Bruner

injury to a member of a sports team may affect the team. Injury events within a team may alter the personnel available to fulfill certain roles and thus disrupt existing group dynamics—for better or worse. Although a range of circumstances can arise to cause unexpected team member absences (e

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Brice Guignard, Annie Rouard, Didier Chollet, Marco Bonifazi, Dario Dalla Vedova, John Hart and Ludovic Seifert

Humans exhibit a large repertoire of patterns of locomotion, dependent on whether they are within a terrestrial or aquatic environment, including: walking or running, when on the ground; and at least four swimming strokes, when in water. According to an ecological dynamics approach, behavior of the