Roger Bartlett

Movement systems as dynamical systems: the functional role of variability and its implications for sports medicine.

In recent years, concepts and tools from dynamical systems theory have been successfully applied to the study of movement systems, contradicting traditional views of variability as noise or error. From this perspective, it is apparent that variability in movement systems is omnipresent and unavoidable due to the distinct constraints that shape each individual’s behaviour. In this position paper, it is argued that trial-to-trial movement variations within individuals and performance differences observed between individuals may be best interpreted as attempts to exploit the variability that is inherent within and between biological systems. That is, variability in movement systems helps individuals adapt to the unique constraints (personal, task and environmental) impinging on them across different timescales. We examine the implications of these ideas for sports medicine, by: (i) focusing on intra-individual variability in postural control to exemplify within-individual real-time adaptations to changing informational constraints in the performance environment; and (ii) interpreting recent evidence on the role of the angiotensin-converting enzyme gene as a genetic (developmental) constraint on individual differences in physical performance.The implementation of a dynamical systems theoretical interpretation of variability in movement systems signals a need to re-evaluate the ubiquitous influence of the traditional ‘medical model’ in interpreting motor behaviour and performance constrained by disease or injury to the movement system. Accordingly, there is a need to develop new tools for providing individualised plots of motor behaviour and performance as a function of key constraints. Coordination profiling is proposed as one such alternative approach for interpreting the variability and stability demonstrated by individuals as they attempt to construct functional, goal-directed patterns of motor behaviour during each unique performance. Finally, the relative contribution of genes and training to between-individual performance variation is highlighted, with the conclusion that dynamical systems theory provides an appropriate multidisciplinary theoretical framework to explain their interaction in supporting physical performance.

The use of performance indicators in performance analysis

The aims of this paper are to examine the application of performance indicators in different sports and, using the different structural definitions of games, to make general recommendations about the use and application of these indicators. Formal games are classified into three categories: net and wall games, invasion games, and striking and fielding games. The different types of sports are also sub-categorized by the rules of scoring and ending the respective matches. These classes are analysed further, to enable definition of useful performance indicators and to examine similarities and differences in the analysis of the different categories of game. The indices of performance are sub-categorized into general match indicators, tactical indicators, technical indicators and biomechanical indicators. Different research examples and the accuracy of their presentation are discussed. We conclude that, to enable a full and objective interpretation of the data from the analysis of a performance, comparisons of data are vital. In addition, any analysis of the distribution of actions across the playing surface should also be presented normalized, or non-dimensionalized, to the total distribution of actions across the area. Other normalizations of performance indicators should also be used more widely in conjunction with the accepted forms of data analysis. Finally, we recommend that biomechanists should pay more attention to games to enrich the analysis of performance in these sports.

Is movement variability important for sports biomechanists

This paper overviews the importance for sports biomechanics of movement variability, which has been studied for some time by cognitive and ecological motor skills specialists but, until quite recently, had somewhat been overlooked by sports biomechanists. The paper considers biomechanics research reporting inter- and intra-individual movement variability in javelin and discus throwing, basketball shooting, and locomotion. The overview does not claim to be comprehensive and we exclude such issues as the theoretical background to movement and coordination variability and their measurement. We overview evidence, both theoretical and empirical, of inter-individual movement variability in seeking to achieve the same task goal, in contrast to the concept of “optimal” movement patterns. Furthermore, even elite athletes cannot reproduce identical movement patterns after many years of training, contradicting the ideas of motor invariance and “representative” trials. We contend that movement variability, far from being solely due to neuromuscular system or measurement “noise” – as sports biomechanists may have previously supposed – is, or could be, functional. Such functionality could allow environmental adaptations, reduce injury risk, and facilitate changes in coordination patterns. We conclude by recommending that sports biomechanists should focus more of their research on movement variability and on important related topics, such as control and coordination of movement, and implications for practice and skill learning.

Advances in the application of information technology to sport performance

This paper overviews the diverse information technologies that are used to provide athletes with relevant feedback. Examples taken from various sports are used to illustrate selected applications of technology-based feedback. Several feedback systems are discussed, including vision, audition and proprioception. Each technology described here is based on the assumption that feedback would eventually enhance skill acquisition and sport performance and, as such, its usefulness to athletes and coaches in training is critically evaluated.

Research design and statistics in biomechanics and motor control

Biomechanics and motor control researchers measure how the body moves and interacts with its environment. The aim of this review paper is to consider some key issues in research methods in biomechanics and motor control. The review is organized into four sections: proposing, conducting, analysing and reporting research. In the first of these, we emphasize the importance of defining a worthy research question and of planning the study before its implementation to prevent later difficulties in the analysis and interpretation of data. In the second section, we cover selection of trial sizes and suggest that using three trials or more may be beneficial to provide more ‘representative’ and valid data. The third section on analysis of data concentrates on effect size statistics, qualitative and numerical trend analysis and cross-correlations. As sample sizes are often small, the use of effect size is recommended to support the results of statistical significance testing. In using cross-correlations, we recommend that scatterplots of one variable against the other, with the identified time lag included, be inspected to confirm that the linear relationship assumption underpinning this statistic is met and, if appropriate, that a linearity transformation be applied. Finally, we consider important information related to the issues above that should be included when reporting research. We recommend reporting checks or corrections for violations of underpinning assumptions, and the effect of these checks or corrections, to assist in advancing knowledge in biomechanics and motor control.

Normalisation of EMG amplitude: an evaluation and comparison of old and new methods

The purpose of this study was to evaluate and compare four different methods of normalising the amplitude of electromyograms (EMGs), from the biceps brachii. Five males performed isotonic contractions of the elbow flexors with an external force of 50 N, 100 N, 150 N and 200 N. These were followed by a single isometric maximal voluntary contraction (MVC) and ten isokinetic MVCs at 0.35 rad s(-1) intervals between 0.35 rad s(-1) and 3.50 rad s(-1). The processed EMGs recorded from the isotonic contractions were normalised by expressing them as a percentage of: (i) the mean (Dynamic Mean Method) and (ii) the peak EMG from the same contraction (Dynamic Peak Method), (iii) the EMG from the isometric MVC (Isometric MVC Method), and (iv) the EMG from an isokinetic MVC at the same elbow angle and angular velocity (Isokinetic MVC Method). The root mean square difference (RMSD) between the outputs of the Isokinetic MVC and Dynamic Mean methods was significantly greater (P<0.05) than between the Isokinetic MVC method and the Dynamic Peak and the Isometric MVC methods. The small (10%) difference between the Isokinetic MVC and the Isometric MVC Methods was a consequence, firstly, of the lack of difference in EMG recorded from the isometric and isokinetic MVCs and, secondly, the consistency in EMG over the range of motion and at different angular velocities of isokinetic MVC. We conclude that only the Isometric and Isokinetic MVC methods should be used to normalise the amplitude of EMGs from the biceps brachii.

The biomechanics of fast bowling in men's cricket: A review

This review concentrates on synthesizing and analysing the biomechanical research which has been carried out on fast bowling in mens cricket. Specifically, it relates to those elements of the bowling technique which contribute towards a fast ball release, the aerodynamics and technique of swing bowling, and the association between fast bowling and lower back injury. With regard to bowling technique, no firm conclusions are drawn on the relationships between elements of the fast bowling technique and ball release speed. Recommendations for future research in this area include intra-player studies to establish the bowler-specific factors which contribute to fast ball release and features of body segment dynamics. There is general agreement that the phenomenon of differential boundary layer separation is the reason for normal and reverse cricket ball swing. Systematic research to establish the essential aspects of the bowling technique which contribute to successful swing bowling is recommended, along with studies of the behaviour of the ball in games to ascertain the effects of ball asymmetries on ball swing. There is sufficient evidence in the literature to establish a strong link between injury to the lower back and the use of the mixed technique. Recommendations are made for screening and intervention to reduce the use of the mixed technique, and for research into other aspects of injury. Fundamental research to develop biomechanical models of the lower back in fast bowling is strongly recommended.

The relationship between basketball shooting kinematics, distance and playing position

Three-dimensional cinematography (100 Hz) was used to establish the relationship between distance and the kinematics of shooting with respect to playing position in basketball. Fifteen subjects, divided into guards, forwards and centres (all n = 5), performed jump shots from each of three distances: 2.74, 4.57 and 6.40 m from the basket. Increases in mean release speed were found as shooting distance increased for all groups. This was due to increased angular velocities of both shoulder flexion and elbow extension and an increased speed of the centre of mass in the direction of the basket. Release angles for the two shorter distances (52-55 degrees) tended to provide the advantage of a steep angle of entry into the basket, whereas those at the longest distance (48-50 degrees) were closer to those requiring the minimum possible release speed. All groups exhibited an earlier timing of release as shooting distance increased, which gave rise to an earlier rotation of the shoulder axis. The more consistent changes in kinematic patterns with changes in shooting distance exhibited by guards as compared to centres would suggest that such adjustments are easier to make for those players who regularly shoot from long range.

Biomechanical Factors Critical for Performance in the Men’s Javelin Throw

SummaryIn the men’s javelin event the athlete throws an 800g implement into a 40° sector. The objective is to throw as far as possible. Compared with most other throwing implements, the javelin is relatively aerodynamic. Even so, the most important release parameter is still the release speed. Maximising this parameter gives the athlete the best chance of attaining success in the event.For an elite thrower, as much as 70% of the release speed of the javelin is developed in the last 0.1 second. As such, the movements of throwers during this period and immediately preceding it have received attention from researchers. It would appear that a thrower’s body position at the instant of final foot strike, his ability to transfer momentum between the lower body and the upper body during the delivery, and coordination of the working body segments in the most effective manner are linked to his success in the event. This paper reviews the most important biomechanical research on the men’s javelin throw and highlights findings such as these which may improve the understanding of how elite javelin throwers achieve success.

The science and medicine of cricket: an overview and update

Abstract Research into the science and medicine underlying cricket performance and injury has progressed since the First World Congress of Science and Medicine in Cricket in 1999. This review covers material on the physiological and psychological demands of the game and preparation for it, the biomechanics and motor control of cricket skills, the psychology of team dynamics, performance analysis and cricket injuries. Technological aspects of cricket equipment are also covered, where such research could influence injury risk or player performance. Fielding remains the least studied of the skills. Much more research needs to be done before we can gain a full understanding of the scientific aspects of the game. There is a need to address common definitions of injury, along with more research into injury mechanisms. Research on batting needs to bring together motor control and biomechanics more fully. The fitness demands of the game are still poorly understood, along with the mechanisms causing fatigue. Evaluation of the efficacy of intervention strategies needs to continue and to develop. The applications of research need to be communicated more to coaches and players — for example, in team dynamics — so that they can be applied, and tested further, in international matches.