The patterning of local variability during the acquisition of a novel whole-body continuous motor skill in young adults

Time-specific convergence and divergence in individual differences in behavior: Theory, protocols and analyzes

Over the years, theoreticians and empiricists working in a wide range of disciplines, including physiology, ethology, psychology, and behavioral ecology, have suggested a variety of reasons why individual differences in behavior might change over time, such that different individuals become more similar (convergence) or less similar (divergence) to one another. Virtually none of these investigators have suggested that convergence or divergence will continue forever, instead proposing that these patterns will be restricted to particular periods over the course of a longer study. However, to date, few empiricists have documented time-specific convergence or divergence, in part because the experimental designs and statistical methods suitable for describing these patterns are not widely known. Here, we begin by reviewing an array of influential hypotheses that predict convergence or divergence in individual differences over timescales ranging from minutes to years, and that suggest how and why such patterns are likely to change over time (e.g., divergence followed by maintenance). Then, we describe experimental designs and statistical methods that can be used to determine if (and when) individual differences converged, diverged, or were maintained at the same level at specific periods during a longitudinal study. Finally, we describe why the concepts described herein help explain the discrepancy between what theoreticians and empiricists mean when they describe the "emergence" of individual differences or personality, how they might be used to study situations in which convergence and divergence patterns alternate over time, and how they might be used to study time-specific changes in other attributes of behavior, including individual differences in intraindividual variability (predictability), or genotypic differences in behavior.

Experience influences kinematic motor synergies: an Uncontrolled manifold approach to simulated Nordic skiing

Motor synergies are defined as central nervous system mechanisms which adjust participating degrees of freedom to ensure dynamic stability (control) of certain performance variables and have been identified during many motor tasks. The potential for synergistic control of individual segments during full-body tasks is often overlooked. Thus, this study compared individual differences in the potential stabilization of multiple performance variables on the basis of experience during a full-body sport activity. Normalized time series of synergy indices from Uncontrolled Manifold analyses on experienced (n = 9) and inexperienced (n = 19) participants were analysed using statistical parametric mapping during simulated Nordic skiing. Regardless of experience, hand, upper arm, and whole-body centre of mass (COM) kinematics were found to be stabilized by kinematic motor synergies. Only experienced Nordic skiers stabilized trunk COM position at all, while trunk COM velocity was stabilized for a longer duration than inexperienced participants. However, inexperienced participants stabilized hand velocity for a greater duration overall and to a greater magnitude during early pull phase than the experienced skiers. That motor synergies for hand and trunk COM velocity differed between experience groups suggests potential utility for these performance variables as indicators of motor skill development for full-body tasks such as Nordic skiing.

Self-directed kinematic adjustments when learning the kettlebell swing in young adults

The kettlebell swing is a complex exercise shown to provide cardiovascular and strength benefits. However, novice kinematic pattern differences might limit the effectiveness of the kettlebell swing to fully realise those benefits. The purpose of this study was to assess how novices self-directed their learning of the kettlebell swing using only an instructional video. Twelve young adults performed kettlebell swings sets over one week. We captured kinematic data of their first sets without practice, sets within-day following practice, and sets one week later following practice. The subjects received no augmented feedback. Ankle, knee, hip, and shoulder mean and variability kinematics were compared. In addition, the relative timing of peak sagittal plane angular velocity of the hip and shoulder was evaluated to determine whether the hips led to the shoulders. Within-day subjects reduced hip and shoulder peak extension, knee and hip peak flexion, and hip peak flexion velocity. Between-day subjects reduced mean hip peak flexion and range of motion, as well as peak knee flexion. Our results suggest novices prioritised improving consistency early in practice and then adjusted their kinematic pattern over the week. Moreover, most subjects transitioned to the hips leading shoulders, suggesting this is a perceivable coordination pattern by intrinsic feedback.

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.

Implications of Optimal Feedback Control Theory for Sport Coaching and Motor Learning: A Systematic Review

Best practice in skill acquisition has been informed by motor control theories. The main aim of this study is to screen existing literature on a relatively novel theory, Optimal Feedback Control Theory (OFCT), and to assess how OFCT concepts can be applied in sports and motor learning research. Based on 51 included studies with on average a high methodological quality, we found that different types of training seem to appeal to different control processes within OFCT. The minimum intervention principle (founded in OFCT) was used in many of the reviewed studies, and further investigation might lead to further improvements in sport skill acquisition. However, considering the homogenous nature of the tasks included in the reviewed studies, these ideas and their generalizability should be tested in future studies.