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Anat V. Lubetzky, Daphna Harel, Helene Darmanin and Ken Perlin

normal and abnormal responses to changing visual cues with eyes open in situations relevant to daily living ( Jeka et al., 2006 ). In the past few years, there have been substantial advancements in virtual reality (VR) technology. The ability to carefully manipulate visual environments has become simpler

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Alba Reguant-Closa, Margaret M. Harris, Tim G. Lohman and Nanna L. Meyer

and macronutrients to body mass (BM), weight categories were defined by gender (60 kg females [f] and 75 kg males [m]). Each sport dietitian created 18 plates. To avoid food waste, half of the plates were created “virtually” on paper, whereas the other half were created with food. For the virtual

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Michael Gay and Semyon Slobounov

dysfunction (structural data) in the brain after trauma. Advances in modalities such as functional neuroimaging, quantitative electroencephalography, and virtual reality–based cognitive testing combined with current clinical batteries of exams such as neuropsychological testing, oculomotor examination, and

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Gunnar Treff, Kay Winkert, Katja Machus and Jürgen M. Steinacker

based on the criteria that would normally cause TERM auto , when activated. The virtual test duration at TERM auto was compared with the actual test duration after TERM exhaust . Metabolic Analysis Gas exchange and ventilation were measured with a Metamax 3x (Cortex Biophysics, Leipzig, Germany) to

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Paolo Taboga, Alena M. Grabowski, Pietro Enrico di Prampero and Rodger Kram

In the 2012 Paralympic 100 m and 200 m finals, 86% of athletes with a unilateral amputation placed their unaffected leg on the front starting block. Can this preference be explained biomechanically? We measured the biomechanical effects of starting block configuration for seven nonamputee sprinters and nine athletes with a unilateral amputation. Each subject performed six starts, alternating between their usual and unusual starting block configurations. When sprinters with an amputation placed their unaffected leg on the front block, they developed 6% greater mean resultant combined force compared with the opposite configuration (1.38 ± 0.06 vs 1.30 ± 0.11 BW, P = .015). However, because of a more vertical push angle, horizontal acceleration performance was equivalent between starting block configurations. We then used force data from each sprinter with an amputation to calculate the hypothetical starting mechanics for a virtual nonamputee (two unaffected legs) and a virtual bilateral amputee (two affected legs). Accelerations of virtual bilateral amputees were 15% slower compared with athletes with a unilateral amputation, which in turn were 11% slower than virtual nonamputees. Our biomechanical data do not explain the starting block configuration preference but they do explain the starting performance differences observed between nonamputee athletes and those with leg amputations.

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Bob W. Kooi and Max Kuipers

The maneuvers of a competition diver on a springboard before takeoff may serve to maximize the height of the flight phase. To simplify analysis, it is often assumed that the diver performs motions at the top of a single degree-of-freedom (DOF) system, usually consisting of one mass and one linear spring. This system is expected to simulate the behavior of the board sufficiently. In this paper we propose a new single DOF system approximating the effects of a board with passable accuracy. This model is applied to three types of springboards to obtain numerical values for their virtual masses at the tip.

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Robert Tibold, Gabor Fazekas and Jozsef Laczko

A three-dimensional (3-D) arm movement model is presented to simulate kinematic properties and muscle forces in reaching arm movements. Healthy subjects performed reaching movements repetitively either with or without a load in the hand. Joint coordinates were measured. Muscle moment arms, 3-D angular acceleration, and moment of inertias of arm segments were calculated to determine 3-D joint torques. Variances of hand position, arm configuration, and muscle activities were calculated. Ratios of movement variances observed in the two conditions (load versus without load) showed no differences for hand position and arm configuration variances. Virtual muscle force variances for all muscles except deltoid posterior and EMG variances for four muscles increased significantly by moving with the load. The greatly increased variances in muscle activity did not imply equally high increments in kinematic variances. We conclude that enhanced muscle cooperation through synergies helps to stabilize movement at the kinematic level when a load is added.

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Wei Zhang, Halla B. Olafsdottir, Vladimir M. Zatsiorsky and Mark L. Latash

We studied the mechanical variables (the grip force and the total moment of force) and multidigit synergies at two levels (the virtual finger-thumb level, VF-TH, and the individual finger level, IMRL) of a hypothetical control hierarchy during accurate rotation of a hand-held instrumented handle. Synergies were defined as covaried changes in elemental variables (forces and moments of force) that stabilize the output at a particular level. Indices of multidigit synergies showed higher values at the hierarchically higher level (VF-TH) for both normal and tangential forces. The moment of force was stabilized at both hierarchical levels during the steady-state phases but not during the movement. The results support the principles of superposition and of mechanical advantage. They also support an earlier hypothesis on an inherent tradeoff between synergies at the two hierarchical levels, although the controller showed more subtle and versatile synergic control than the one hypothesized earlier.

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Vanda Correia, Duarte Araújo, Alan Cummins and Cathy M. Craig

This study used a virtual, simulated 3 vs. 3 rugby task to investigate whether gaps opening in particular running channels promote different actions by the ball carrier player and whether an effect of rugby expertise is verified. We manipulated emergent gaps in three different locations: Gap 1 in the participant’s own running channel, Gap 2 in the first receiver’s running channel, and Gap 3 in the second receiver’s running channel. Recreational, intermediate, professional, and nonrugby players performed the task. They could (i) run with the ball, (ii) make a short pass, or (iii) make a long pass. All actions were digitally recorded. Results revealed that the emergence of gaps in the defensive line with respect to the participant’s own position significantly influenced action selection. Namely, “run” was most often the action performed in Gap 1, “short pass” in Gap 2, and “long pass” in Gap 3 trials. Furthermore, a strong positive relationship between expertise and task achievement was found.

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Joel R. Martin, Mark L. Latash and Vladimir M. Zatsiorsky

This study investigated the effects of modifying contact finger forces in one direction—normal or tangential—on the entire set of the contact forces, while statically holding an object. Subjects grasped a handle instrumented with finger force-moment sensors, maintained it at rest in the air, and then slowly: (1) increased the grasping force, (2) tried to spread fingers apart, and (3) tried to squeeze fingers together. Analysis was mostly performed at the virtual finger (VF) level (the VF is an imaginable finger that generates the same force and moment as the four fingers combined). For all three tasks there were statistically significant changes in the VF normal and tangential forces. For finger spreading/squeezing the tangential force neutral point was located between the index and middle fingers. We conclude that the internal forces are regulated as a whole, including adjustments in both normal and tangential force, instead of only a subset of forces (normal or tangential). The effects of such factors as EFFORT and TORQUE were additive; their interaction was not statistically significant, thus supporting the principle of superposition in human prehension.