The evolving high bar longswing in elite gymnasts of three age groups.

Chronological age classifies elite male gymnasts into developmental performance classifications: senior (18+ years), junior (14-18 years) and development (8-14 years). Here, we examine the influence of age and experience on the biomechanics of the high bar longswing across classifications. Joint angular kinematics and kinetics were obtained from 30 gymnasts performing three sets each of eight consecutive longswings. Differences between groups and relations between age, experience and key biomechanical variables were correlated. Kinetic variables and range of motion of the hip and knee were highest for development gymnasts. In all age groups, a dominant shoulder kinetic contribution was found, although circle location of the peak joint kinetics occurred earliest for junior gymnasts. Hip work contributed more prominently in development gymnasts. Age and experience were positively correlated to an increase in peak shoulder moments and powers and negatively correlated to peak hip and knee moments. The findings reveal that age and experience combine to influence the functional phase, joint kinematics and relative joint kinetic contribution, particularly with the senior group demonstrating a shoulder dominant technique. Changes in musculoskeletal loading across the age groups suggest that factors such as relative strength and practice may have influenced this joint mode transition of the longswing.

Strength training as a dynamical model of motor learning.

This paper outlines a framework for strength training as a dynamical model of perceptual-motor learning. We show, with emphasis on fixed-point attractor dynamics, that strength training can be mapped to the general dynamical principles of motor learning that arise from the constraints on action, including the distribution of practice/training. The time scales of the respective dynamics of performance change (increment and decrement) in discrete strength training and motor learning tasks reveal superposition of exponential functions in fixed-point dynamics, but distinctive attractor and parameter dynamics in oscillatory limit cycle and more continuous tasks, together with unique timescales to process influences (including practice, learning, strength, fitness, fatigue, warm-up decrement). Increments and decrements of strength can be viewed within a dynamical model of change in motor performance that reflects the integration of practice and training processes at multiple levels of learning and skill development.

Narrowing the coordination solution space during motor learning standardizes individual patterns of search strategy but diversifies learning rates.

Constraints on practice can benefit motor learning by guiding the learner towards efficient coordination patterns, but can also narrow the potential solution space of coordination and control. The aim of this paper was to investigate whether narrowing the solution space through more restrictive task constraints limits the expression of potential exploratory behaviours during the learning process, identified using Drifting Markov Models. In a breaststroke swimming task, the change in interlimb coordination of 7 learners practicing for 16 lessons over 2 months was analysed to quantify motor exploration and identify periods of metastable regimes of coordination. Results showed that the observed exploratory dynamics were highly individual both in terms of range of exploration and in the patterns of search. The more restrictive task constraints did not impair the amount of exploration but rather channelled the exploration around a few selected patterns. In addition, restraining the nature of the exploratory process increased the inter-individual differences of the learning rate. Although manipulating the task constraints during learning can help learners to escape from the behavioural consequences of their intrinsic dynamics, maintaining a broad solution space for a diversity of coordination patterns to emerge was key to fostering effective exploration of individual coordination solutions.

Task and Informational Constraints on Search Strategies: Testing the Idea of Convergence to Tolerant Regions.

The experiment reported was designed to investigate the interaction of information and force variability on the evolving search strategy, specifically testing the hypothesis of convergence to tolerant regions. Participants were required to produce proportional bimanual isometric force output over three days of practice, with no prespecified force target and where performance was more tolerant to force variability at higher forces. The duration of intermittent visual feedback was manipulated to test the effects of information and force variability on the search process and the resulting sensitivity to tolerant regions of the task space. The findings showed that just under half of the participants exploited more tolerant regions and that this was predicted by the initial force conditions. Different characterizations of the individual search patterns were also predicted by inherent force-dependent variability and initial force conditions. Visual intermittency feedback did not affect the time-dependent properties of the search process but did influence the within-trial variability. Our findings suggest that the attraction to tolerant regions needs to be considered within the interactions of the different categories of constraints on the search process.

The Reciprocal Nature of Fitts' Law in Space and Time.

Human movement takes place in both space and time so that measures of movement accuracy in space are made with respect to time, and vice-versa providing a foundation to the proposal of the complementarity of spatial and temporal error in aiming movements. We examined this hypothesis in both the standard Fitts and Peterson discrete movement speed-accuracy protocol that requires moving to stop within a fixed spatial target (distance (D) with target bandwidth (WD) in an emergent movement time (T) and, also in the reciprocal and novel space-time protocol introduced here that required moving for a fixed temporal target goal T with bandwidth of WT with an emergent D. Experiment 1 examined a range of D conditions (45, 100, 180, 280, and 405 mm with bandwidth WD ±5 mm) within the Fitts' Law discrete spatial accuracy protocol to provide compatible spacetime boundary conditions for the reciprocal spacetime protocol in Experiment 2 that examined the effect of target time (T - 250, 460, 670, and 880 ms each with bandwidth WT ±50 ms) on the emergent D. The findings showed that the spatial and temporal error profiles in Experiment 2 were consistent with exchanging D and T in Fitts' Law Equation. This provides evidence for the reciprocal nature of the spacetime error functions in Fitts' type movement aiming protocols and is compatible with the reciprocal profiles of spatial and temporal errors in other classes of movement aiming tasks.

Task Specific and General Patterns of Joint Motion Variability in Upright- and Hand-Standing Postures.

The preservation of static balance in both upright- and hand-stance is maintained by the projection of center of mass (CM) motion within the region of stability at the respective base of support. This study investigated, from a degrees of freedom (DF) perspective, whether the stability of the CM in both upright- and hand-stances was predicted by the respective dispersion and time-dependent regularity of joint (upright stance-ankle, knee, hip, shoulder, neck; hand stance-wrist, elbow, shoulder, neck) angle and position. Full body three-dimensional (3D) kinematic data were collected on 10 advanced level junior female gymnasts during 30 s floor upright- and hand-stands. For both stances the amount of the dispersion of joint angle and sway motion was higher than that of the CM and center of pressure (CP) with an inverse relation to time-dependent irregularity (SampEn). In upright-standing the variability of neck motion in the anterior-posterior direction was significantly greater than that of most joints consistent with the role of vision in the control of quiet upright posture. The findings support the proposition that there are both task specific and general properties to the global CM control strategy in the balance of upright- and hand-standing induced by the different active skeletal-muscular organization and the degeneracy revealed in the multiple distributional variability patterns of the joint angle and position in 3D.

Instructions on Task Constraints Mediate Perceptual-Motor Search and How Movement Variability Relates to Performance Outcome.

Movement variability has been postulated to afford perception of the perceptual motor workspace and to be directly linked to improved performance. Here, we investigated how instructions mediate the search process and the relation between performance outcome and movement variability. We used a novel bimanual force tracking task where zero error was achieved via proportional output between the hands. Participants were either instructed or not as to how to coordinate their force output to achieve this goal, but the goal to minimize error was explained to all participants. The provision of instructions restricted the overall area of the task space that was searched. Moreover, the time dependent properties of the search were influenced; where instructions increased the likelihood that participants would produce a higher force level over practice. Multiple regression revealed that variability was positively correlated with performance outcome, but the strength of this relation was dependent on instructions and individual search strategies. The findings are consistent with the view that information through instructions shapes individual emergent perceptual-motor search strategies that in turn mediate how movement variability relates to performance outcome.

Are Sub-Movements Induced Visually in Discrete Aiming Tasks?

There is a long-held view that discrete movements aimed to a target are composed of a sequence of movement units (sub-movements) that have different roles in motor control (e.g., initial impulse, error correction and movement termination) depending on the task constraints (e.g., spatial-temporal requirements). Here we report findings from the manipulation of vision/no-vision on the prevalence and type of sub-movements in discrete movement tasks over a range of space-time task criteria. The presence of vison resulted in longer movement times compared to the no-vision counterpart in time-matching tasks. A similar vision effect was observed in the highest Index of Difficulty for time-minimization tasks. Conditions that resulted/required longer movement times demonstrated more pre-velocity-peak and post-velocity-peak types of sub-movements whereas short movement times increased the likelihood of overshooting sub-movements. The present study results are consistent with the idea that movement time is the variable associated with changes in sub-movement profiles.

NCS Assessments of the Motor, Sensory, and Physical Health Domains.

As part of the National Children's Study (NCS) comprehensive and longitudinal assessment of the health status of the whole child, scientific teams were convened to recommend assessment measures for the NCS. This manuscript documents the work of three scientific teams who focused on the motor, sensory, or the physical health aspects of this assessment. Each domain team offered a value proposition for the importance of their domain to the health outcomes of the developing infant and child. Constructs within each domain were identified and measures of these constructs proposed. Where available extant assessments were identified. Those constructs that were in need of revised or new assessment instruments were identified and described. Recommendations also were made for the age when the assessments should take place.

Teaching Children's Motor Skills for Team Games Through Guided Discovery: How Constraints Enhance Learning.

In this paper we examine the role of instructional strategies as constraints within a discovery learning framework for the teaching of open skill team ball games to elementary school-aged children. The cohesive and adaptive integration of constraints (individual, environment, and task) by practitioners of movement and physical activity (instructor, teacher, coach) is proposed as the pathway to exploiting the effectiveness of guided discovery learning. The qualitative analysis of the practical instantiations of this framework by expert teachers is examined with respect to the learning of open skill team invasion games (e.g., basketball, soccer). The primary constraints to action in this learning-teaching developmental framework are coordinated so as to keep the self-organization of skill development (movement pattern and tactics) continually evolving, while preserving the child's motivation and enjoyment for the expanding repertoire and performance capacity of his/her perceptual-motor skills. In this open skill and elementary school age-related context, generality and specificity are both necessary and complementary in the expression of task, skill and practice influences on motor learning and performance.

Establishing Task-Relevant MVC Protocols for Modelling Sustained Isometric Force Variability: A Manual Control Study.

The present study examined how prevalent methods for determining maximal voluntary contraction (MVC) impact the experimentally derived functions of graded force-force variability. Thirty-two young healthy subjects performed continuous isometric force tracking (20 s trials) at 10 target percentages (5-95% MVC) normalized to a conventional discrete-point (n = 16), or sustained (n = 16) MVC calculation. Distinct rates and magnitudes of change were observed for absolute variability (standard deviation (SD), root mean squared error (RMSE)), tracking error (RMSE, constant error (CE)), and complexity (detrended fluctuation analysis (DFA)) (all p < 0.05) of graded force fluctuations between the MVC groups. Differential performance strategies were observed beyond ~65% MVC, with the discrete-point group minimizing their SD at force values below that of the criterion target (higher CE/RMSE). Moreover, the sustained group's capacity to minimize SD/RMSE/CE corresponded to a more complex structure in their force fluctuations. These findings reveal that the time component of MVC estimation has a direct influence on the corrective strategies supporting near-maximal manual force control. While discrete MVC protocols predominate in the study of manual strength/endurance/precision, a 1:1 MVC-task mapping appears more to be ecologically valid if visuo-motor precision outcomes are of central importance.

Exploration of the Specificity of Motor Skills Hypothesis in 7-8 Year Old Primary School Children: Exploring the Relationship Between 12 Different Motor Skills From Two Different Motor Competence Test Batteries.

This study examined the specificity hypothesis by examining the association between two specific motor competence test batteries [Movement Assessment Battery for Children (MABC) and Test of Motor Competence (TMC)] in a sample of young children. In addition, we explored the factorial structure of the MABC and TMC. A total of 80 children participated in the study (38 girls and 42 boys) with a mean chronological age of 7.9 years (SD 0.55). The correlation between total score MABC and total z-score TMC was r = 0.46. In general, low pair-wise correlations (r 2 < 0.20) between the different motor tasks were found. The highest correlation was between the placing bricks and building bricks r = 0.45 (TMC); the stork balance and jumping in squares r = 0.45 (MABC). These low pair-wise relations of items are consistent with findings from younger and older children's age-related motor competence test batteries. Principal components analysis (PCA) showed that the 1st component accommodated 25% of the variance and was dominated in the top five variable weightings by items of the MABC test; whereas the 2nd component accommodated 12% of the variance with the higher weightings all from the TMC test. The findings provide evidence with children for specificity rather than generality in learning motor skills a viewpoint that has predominantly been driven by adult learning studies. The PCA revealed that the MABC and TMC are testing different properties of children's motor competence though in both cases the variance accounted for is relatively modest, but generally higher than the motor item pair-wise correlation.

Learning the High Bar Longswing:I. Task Dynamics and Emergence of the Coordination Pattern.

We studied novice gymnasts (N = 25) learning to form the longswing movement coordination pattern. The focus was the emerging behavioural organisation of centre of mass (CM) dynamics and the relative phase of the bar-CM angular motion. Seven novices learned a complete longswing by the end of the study, 8 novices showed no improvement in proportion of circle completed, and the remainder produced modest but persistent increments of final swing height without achieving a full circle. The radial angular velocity generated in the free fall phase and the circle location of bar-CM relative phase progressively and predominantly predicted circle completion. Bar-CM relative phase produced a consistent qualitative relation within- and between-subjects characteristic of a collective variable with the bar leading the CM on the initial downward antiphase segment and the CM leading on the upward antiphase segment. The ratio of these phases was related by the last practice session to degree of circle completion. The findings showed strong individual differences in the effect of practice on the early steps of learning the movement coordination where the progressive emergence of the longswing circle is driven by exploiting the positive- and minimising the negative-influence of gravity on the bar-CM coordination dynamics (candidate collective variable).

Attractor dynamics of elite performance: the high bar longswing.

Combining biomechanics and motor control, the aim of this study was to investigate the limit cycle dynamics during the high bar longswing across the UK elite gymnastics pathway age groupings. Senior, junior and development gymnasts (N = 30) performed three sets of eight consecutive longswings on the high bar. The centre of mass motion was examined through Poincaré plots and recurrence quantification analysis exploring the limit cycle dynamics of the longswing. Close to one-dimensional limit cycles were displayed for the senior (correlation dimension (CD) = 1.17 ± .08), junior (CD = 1.26 ± .08) and development gymnasts (CD = 1.33 ± .14). Senior elite gymnasts displayed increased recurrence characteristics in addition to longer longswing duration (p < .01) and lower radial angular velocity of the mass centre (p < .01). All groups of gymnasts had highly recurrent and predictable limit cycle characteristics. The findings of this research support the postulation that the further practice, experience and individual development associated with the senior gymnasts contribute to the refinement of the longswing from a nonlinear dynamics perspective. These findings support the idea of functional task decomposition informing the understanding of skill and influencing coaches' decisions around skill development and physical preparation.

Learning the high bar longswing:II. energetics and the emergence of the coordination pattern.

This paper is Part II of a study of the effects of practice on young adult novice gymnasts learning the movement coordination pattern of the longswing. The focus was the early stage of learning a critical component of the longswing, namely: through joint motion to inject mechanical energy into the upswing segment effectively to complete the longswing circle. Twenty-five novice male gymnasts received expert instruction while practicing two sessions a week for 3 weeks between a pre- and a post-practice assessment test trial. Seven novices completed a full circle by the end of Test 4. Completion of the longswing was positively related to the angular velocity generated in the gravity driven free fall of the initial segment and the greater rate of energy input in the upward segment. A successful performance in terms of the emergent movement pattern requires coordination of the onset, rate and level of energy input to counterbalance the negative influence of gravity on the second half upwards segment. The development of the complete longswing through the emergence of the collective variable dynamics (Paper 1) and biomechanical energetics of the gymnast (Paper 2) informs coaches, scientists and clinicians regarding task decomposition and learning the longswing.

Atypical neural processing during the execution of complex sensorimotor behavior in autism.

Stereotyped behavior is rhythmic, repetitive movement that is essentially invariant in form. Stereotypy is common in several clinical disorders, such as autism spectrum disorders (ASD), where it is considered maladaptive. However, it also occurs early in typical development (TD) where it is hypothesized to serve as the foundation on which complex, adaptive motor behavior develops. This transition from stereotyped to complex movement in TD is thought to be supported by sensorimotor integration. Stereotypy in clinical disorders may persist due to deficits in sensorimotor integration. The present study assessed whether differences in sensorimotor processing may limit the expression of complex motor behavior in individuals with ASD and contribute to the clinical stereotypy observed in this population. Adult participants with ASD and TD performed a computer-based stimulus-tracking task in the presence and absence of visual feedback. Electroencephalography was recorded during the task. Groups were compared on motor performance (root mean square error), motor complexity (sample entropy), and neural complexity (multiscale sample entropy of the electroencephalography signal) in the presence and absence of visual feedback. No group differences were found for motor performance or motor complexity. The ASD group demonstrated greater neural complexity and greater differences between feedback conditions than TD individuals, specifically in signals relevant to sensorimotor processing. Motor performance and motor complexity correlated with clinical stereotypy in the ASD group. These findings support the hypothesis that individuals with ASD have differences in sensorimotor processing when executing complex motor behavior and that stereotypy is associated with low motor complexity.

Skill level and the free moment during a pistol aiming task.

The present study investigated the transversal rotation of body and its relation to the horizontal movement for expert shooters and novices in a pistol aiming task. Participants stood on a force plate with an air pistol and aimed it to the centre of a target, positioned 1.4 m above the floor and 10 m away from the force plate, for 30 s as accurately as possible. The results revealed that the novice group showed greater transversal body variability represented by the free moment (FM) than the expert group. Correlation analysis showed that there is tight coupling between the FM and centre of pressure both in the anterior-posterior and medio-lateral directions for the expert group while only strong coupling of that in the anterior-posterior direction for the novice group. The findings suggest that FM is a critical factor to accurately aim the pistol on the target and there is a different postural strategy, in terms of the body motion in the transversal and horizontal space, as a function of skill level to realise success in the pistol aiming task.

Multifractal roots of suprapostural dexterity.

Visually guided postural control emerges in response to task constraints. Task constraints generate physiological fluctuations that foster the exploration of available sensory information at many scales. Temporally correlated fluctuations quantified using fractal and multifractal metrics have been shown to carry perceptual information across the body. The risk of temporally correlated fluctuations is that stable sway appears to depend on a healthy balance of standard deviation (SD): too much or too little SD entails destabilization of posture. This study presses on the visual guidance of posture by prompting participants to quietly stand and fixate at distances within, less than, and beyond comfortable viewing distance. Manipulations of the visual precision demands associated with fixating nearer and farther than comfortable viewing distance reveals an adaptive relationship between SD and temporal correlations in postural fluctuations. Changing the viewing distance of the fixation target shows that increases in temporal correlations and SD predict subsequent reductions in each other. These findings indicate that the balance of SD within stable bounds may depend on a tendency for temporal correlations to self-correct across time. Notably, these relationships became stronger with greater distance from the most comfortable viewing and reaching distance, suggesting that this self-correcting relationship allows the visual layout to press the postural system into a poise for engaging with objects and events. Incorporating multifractal analysis showed that all effects attributable to monofractal evidence were better attributed to multifractal evidence of nonlinear interactions across scales. These results offer a glimpse of how current nonlinear dynamical models of self-correction may play out in biological goal-oriented behavior. We interpret these findings as part of the growing evidence that multifractal nonlinearity is a modeling strategy that resonates strongly with ecological-psychological approaches to perception and action.

Bidirectional causal control in the dynamics of handstand balance.

The aim of this study was to identify motor control solutions associated with the ability to maintain handstand balance. Using a novel approach, we investigated the dynamical interactions between centre of pressure (CoP) and centre of mass (CoM) motion. A gymnastics cohort was divided into a 'less skilled' group, who held handstands for 4-6 s, and a 'more skilled' group, who held handstands in excess of 10 s. CoP-CoM causality was investigated in anterior-posterior (AP) and medio-lateral (ML) directions, in addition to time-space, time-frequency and Hurst Exponent (H) analyses. Lower AP CoP to CoM causal drive and lower H values (> 0.6) indicated the more skilled gymnasts were less reliant on CoP mechanics to drive CoM motion. More skilled performance demonstrated greater adaptability through use of reactive, as opposed to anticipatory, control strategies. Skilled performers additionally exploited mechanical advantages in ML (e.g. a wider base of support), compared to the less skilled athletes. A multiple regression analysis revealed H and frequency domain measures to be better predictors of handstand balance duration than time-space domain measures. The study findings highlight the advantage of an adaptable motor control system with a directional profile, and provide new insight into the clear, measurable footprint of CoP on the dynamics of CoM.

Collective Variables and Task Constraints in Movement Coordination, Control and Skill.

In this paper we review studies that have identified collective variables (order parameters) in movement coordination, control and skill with emphasis on whole-body multiple joint degree of freedom (DF) tasks. Collective variables of a dynamical system have been proposed formally and informally from a diverse set of perceptual-motor tasks, from which we emphasize: bimanual coordination, locomotion (pedalo, walking, running, bicycle riding), roller ball task, static (quiet standing) and dynamic (moving on a ski-simulator) balance, grasping, and juggling. Several types of candidate collective variables have been identified, including: relative phase, frequency ratio, number of hands active in grasping, synchrony, learning rate and relative timing. There is a strong influence of the task goal in determining the collective variable that can be body or environment relative. The emergence of the task relevant collective variable is typically in the early stage of skill learning where subjects through practice adapt movement organization to realize a never previously produced movement coordination pattern. Throughout, the paper elaborates on open theoretical, experimental and analysis issues for collective variables in the context of task constraints and Bernstein's (1967) view of skill acquisition as learning to master redundant DF.