Diagnosing fatigue in gait patterns by support vector machines and self-organizing maps

The aim of the study was to train and test support vector machines (SVM) and self-organizing maps (SOM) to correctly classify gait patterns before, during and after complete leg exhaustion by isokinetic leg exercises. Ground reaction forces were derived for 18 gait cycles on 9 adult participants. Immediately before the trials 7–12, participants were required to completely exhaust their calves with the aid of additional weights (44.4 ± 8.8 kg). Data were analyzed using: (a) the time courses directly and (b) only the deviations from each individual’s calculated average gait pattern. On an inter-individual level the person recognition of the gait patterns was 100% realizable. Fatigue recognition was also highly probable at 98.1%. Additionally, applied SOMs allowed an alternative visualization of the development of fatigue in the gait patterns over the progressive fatiguing exercise regimen.     

The effect of local kinematic changes on anticipation judgments

Skilled tennis players rely on a more global than local perceptual strategy when anticipating an opponent’s shot direction in tennis (Williams, Huys, Cañal-Bruland, & Hagemann, 2009). Global perceptual strategy refers to the pick-up of dynamic information across different body areas rather than from a single source such as the arm or racket. We extend previous work by examining the spatiotemporal characteristics of visual information pick-up when anticipating shot direction in tennis. We perturbed information from various body locations by interchanging the dynamics of selected areas with those from strokes played to the opposite side of the court. In addition, we presented each manipulation under four different temporal occlusion conditions (from 240 ms prior to racket-ball contact) to examine the time course of information extraction. Skilled tennis players outperformed less skilled counterparts in predicting shot direction, even at early phases of the opponent’s motion. Moreover, skilled players showed significant decrements in performance when the arms and racket were perturbed, highlighting the relevance of distal information when anticipating opponents’ intentions.     

Action specificity increases anticipatory performance and the expert advantage in natural interceptive tasks

The relationship between perception-action coupling and anticipatory skill in an interceptive task was examined using an in-situ temporal occlusion paradigm. Skilled and novice cricket batsmen were required to predict the direction of balls bowled towards them under four counterbalanced response conditions of increasing perception-action coupling: (i) verbal, (ii) lower-body movement only, (iii) full-body movement (no bat), and (iv) full-body movement with bat (i.e., the usual batting response). Skilled but not novice anticipation was found to improve as a function of coupling when responses were based on either no ball-flight, or early ball-flight information, with a response requiring even the lowest degree of body movement found to enhance anticipation when compared to a verbal prediction. Most importantly, a full-body movement using a bat elicited greater anticipation than an equivalent movement with no bat. This result highlights the important role that the requirement and/or opportunity to make bat-ball interception may play in eliciting skill differences for anticipation. Results verify the importance of using experimental conditions and task demands that closely reflect the natural performance environment in order to reveal the full nature of the expert advantage.     

Inter-individual variability of forces and modular muscle coordination in cycling: A study on untrained subjects

The aim of this study was to investigate the muscle coordination underlying pedaling in untrained subjects by using the muscle synergies paradigm, and to connect it with the inter-individual variability of EMG patterns and applied forces. Nine subjects performed a pedaling exercise on a cycle-simulator. Applied forces were recorded by means of instrumented pedals able to measure two force components. EMG signals were recorded from eight muscles of the dominant leg, and Nonnegative Matrix Factorization was applied to extract muscle synergy vectors W and time-varying activation coefficients H. Inter-individual variability was assessed for EMG patterns, force profiles, and H. Four modules were sufficient to reconstruct the muscle activation repertoire for all the subjects (variance accounted for >90% for each muscle). These modules were found to be highly similar between subjects in terms of W (mean r = .89), while most of the variability in force profiles and EMG patterns was reflected, in the muscle synergy structure, in the variability of H. These four modules have a functional interpretation when related to force distribution along the pedaling cycle, and the structure of W is shared with that present in human walking, suggesting the existence of a modular motor control in humans.     

Anticipation skill and susceptibility to deceptive movement

The ability to detect deceptive movement was examined in skilled and novice rugby players. Participants (14 per group) attempted to predict direction change from video of expert and recreational rugby players changing direction with and without deceptive movement. Confidence associated with judgments was recorded on each trial to seek evidence regarding use of inferential (heuristic-based) and direct-perceptual (invariant-based) judgments. Novices were found to be susceptible to deceptive movement whereas skilled participants were not; however, both skilled and novice participants were more confident on trials containing deceptive movement. The data suggest that the skill-level difference in sensitivity to advance visual information extends to deceptive information. The implications of this finding, and the importance of considering the underlying process of anticipation skill, are discussed.     

Evolution of match performance parameters for various playing positions in the English Premier League

This study aimed to investigate position-specific evolution of physical and technical performance parameters in the English Premier League (EPL). Match performance observations (n = 14700) were collected using a multiple-camera computerized tracking system across seven seasons (2006–07 to 2012–13). Data were analyzed relative to five playing positions: central defenders (n = 3792), full backs (n = 3420), central midfielders (n = 3200), wide midfielders (n = 2136) and attackers (n = 2152). High-intensity running distance increased in the final season versus the first season in all playing positions (p < .05, ES: 0.9–1.3) with full backs displaying the greatest increase (∼36% higher in 2012–13). Similar trends were observed for sprint distance with full backs demonstrating the most pronounced increase across the seven seasons (36–63%, p < .001, ES: 0.8–1.3). Central players (central defenders and midfielders) illustrated the most pronounced increases in total passes and pass success rate (p < .05, ES: 0.7–0.9) whilst wide players (full backs and wide midfielders) demonstrated only small-moderate increases in total passes and pass success rate (p < .05, ES: 0.6–0.8). The data demonstrates that evolving tactics in the EPL have impacted on the physical demands of wide players and the technical requirements of central players. These findings could be used for talent identification or position-specific physical and technical training.     

Vortex re-capturing and kinematics in human underwater undulatory swimming

To maximize swimming speed athletes copy fish undulatory swimming during the underwater period after start and turn. The anatomical limitations may lead to deviations and may enforce compensating strategies. This has been investigated by analyzing the kinematics of two national female swimmers while swimming in a still water pool. Additionally, the flow around and behind the swimmers was measured with the aid of time-resolved particle image velocimetry (TR-2D-PIV). As compared to fish, the swimmers used undulatory waves characterized by much higher Strouhal numbers but very similar amplitude distributions along the body and Froude efficiencies. Vortices generated in the region of strongly flexing joints are suitable to be used pedally to enhance propulsion (vortex re-capturing). Complementing studies using numerical and technical modeling will help us to probe the efficiency of observed mechanisms and further improvements of the human strategy.     

Energy expenditure and enjoyment of small-sided soccer games in overweight boys

When space is limited, it would be preferable to play multiple small-sided soccer games (SSG) simultaneously on small courts, rather than a single game, to maximise participation. Given that the layouts of most gymnasiums incorporate several badminton courts, we examined whether energy expenditure and enjoyment of SSG on a badminton court (6.1 × 13.4 m) were comparable to larger court dimensions (volleyball and basketball courts; 9 × 18 m and 14.2 × 26.5 m, respectively). Twelve overweight boys played 30 min three-a-side SSG on each court in a counterbalanced design. During SSG, energy expenditure was estimated via accelerometry, heart rate was monitored and ratings of perceived exertion (RPE) and enjoyment were obtained. Energy expenditure was similar between badminton and volleyball courts, but lower than the basketball court (p < .05). Mean% HR_max was significantly lower on the badminton court than the volleyball and basketball courts (p < .05). There was no effect of court size on RPE or enjoyment (p > .05). These results suggest that it may be preferable to play SSG on a larger court when space is available. Alternatively, when space is limited the difference in energy expenditure between court sizes can be accounted for by an additional 2.3 min of play on a badminton court.     

Inter-individual variability in the upper-lower limb breaststroke coordination

The aim of the present study was to examine inter-individual variability in upper-lower limb breaststroke coordination. First, inter-individual variability was compared between recreational and comparative swimmers. Second, as recreational swimmers revealed more variable inter-limb coordination than competitive swimmers, inter-individual variability was assessed among recreational swimmers to identify coordination profiles. The elbow-knee continuous relative phase (CRP) was used to analyze upper-lower limbs coupling during a breaststroke cycle. Twenty-four recreational and twenty-four competitive swimmers swam 25 m at 80% of their maximal speed. Underwater and aerial side views were mixed and genlocked. Angular position, velocity and CRP were calculated for the knee and elbow joints by digitizing body markers from the side view. The kinematics of three cycles were filtered, averaged and normalized in terms of percentage of total cycle duration. The topography of the mean CRP curve of the recreational swimmers resembled a ‘W-shape’, whereas an ‘inverse U-shape’ was seen in the competitive swimmers. However, higher inter-individual variability was observed among the recreational swimmers than among the competitive swimmers (38.1° vs. 19.4°; p < .05), suggesting that several profiles of inter-limb coordination may exist in recreational swimmers. Coordination profiling showed that three clusters could classify the recreational swimmers.