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.     

Confidence crisis of results in biomechanics research

Many biomechanics studies have small sample sizes and incorrect statistical analyses, so reporting of inaccurate inferences and inflated magnitude of effects are common in the field. This review examines these issues in biomechanics research and summarises potential solutions from research in other fields to increase the confidence in the experimental effects reported in biomechanics. Authors, reviewers and editors of biomechanics research reports are encouraged to improve sample sizes and the resulting statistical power, improve reporting transparency, improve the rigour of statistical analyses used, and increase the acceptance of replication studies to improve the validity of inferences from data in biomechanics research. The application of sports biomechanics research results would also improve if a larger percentage of unbiased effects and their uncertainty were reported in the literature.     

Significant and meaningful effects in sports biomechanics research

Errors in statistical analysis of multiple dependent variables and in documenting the size of effects are common in the scientific and biomechanical literature. In this paper, I review these errors and several solutions that can improve the validity of sports biomechanics research reports. Studies examining multiple dependent variables should either control for the inflation of Type I errors (e.g. Holm's procedure) during multiple comparisons or use multivariate analysis of variance to focus on the structure and interaction of the dependent variables. When statistically significant differences are observed, research reports should provide confidence limits or effect sizes to document the size of the effects. Authors of sports biomechanics research reports are encouraged to analyse and present their data accounting for the experiment-wise Type I error rate, as well as reporting data documenting the size or practical significance of effects reaching their standard of statistical significance.     

A review of batting in men’s cricket

In this review, we critically evaluate the scientific research into the morphology and physiology of cricket batsmen. We consider all aspects of the motor control of this skill, in the context of research into dynamic interceptive actions, the biomechanics (kinematics and kinetics) of the various phases of batting strokes and injuries to batsmen. Some attention is also devoted to batting equipment and to psychological factors in batting. Because of the lack of published scientific research into women's cricket, this review focuses on the men's game and covers research on batsmen of various playing standards. For the future, we see as a high priority research into injury mechanisms, rather than simple injury statistics, and the role of cricket equipment design in injury prevention. A second priority is for multi- or inter-disciplinary research, linking the biomechanics of batting to the underlying motor control of the movements and the effect of environmental information. Biomechanical studies of the variability of the batsman's movements are needed, and these should be related to the compensatory variability proposal of ecological psychology. Clearly, there is also a need for scientific research into batting in women's cricket, which has been inadequately researched to date.     

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.     

A review of batting in men's cricket

In this review, we critically evaluate the scientific research into the morphology and physiology of cricket batsmen. We consider all aspects of the motor control of this skill, in the context of research into dynamic interceptive actions, the biomechanics (kinematics and kinetics) of the various phases of batting strokes and injuries to batsmen. Some attention is also devoted to batting equipment and to psychological factors in batting. Because of the lack of published scientific research into women's cricket, this review focuses on the men's game and covers research on batsmen of various playing standards. For the future, we see as a high priority research into injury mechanisms, rather than simple injury statistics, and the role of cricket equipment design in injury prevention. A second priority is for multi- or inter-disciplinary research, linking the biomechanics of batting to the underlying motor control of the movements and the effect of environmental information. Biomechanical studies of the variability of the batsman's movements are needed, and these should be related to the compensatory variability proposal of ecological psychology. Clearly, there is also a need for scientific research into batting in women's cricket, which has been inadequately researched to date.     

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.     

Understanding and measuring coordination and control in kicking skills in soccer: Implications for talent identification and skill acquisition

In this review, we explore the role of motor control and biomechanics in developing an understanding of soccer skills using kicking as the main vehicle. The links between these sub-disciplines of sport science have not been well established in the past because of an emphasis on cognitive processes in traditional accounts of motor behaviour. We argue that a dynamical systems interpretation of the processes of coordination and control in movements with multiple degrees of freedom signals a new era in the relationship between the sub-disciplines of motor control and biomechanics. Although research on coordination and control of soccer skills is currently sparse, there are indications that the relationship between motor control and biomechanics could form a significant component of scientific programmes in talent identification and skill development. Further interdisciplinary work is needed to enhance understanding of coordination and control of soccer skills.     

Understanding and measuring coordination and control in kicking skills in soccer: implications for talent identification and skill acquisition

In this review, we explore the role of motor control and biomechanics in developing an understanding of soccer skills using kicking as the main vehicle. The links between these sub-disciplines of sport science have not been well established in the past because of an emphasis on cognitive processes in traditional accounts of motor behaviour. We argue that a dynamical systems interpretation of the processes of coordination and control in movements with multiple degrees of freedom signals a new era in the relationship between the sub-disciplines of motor control and biomechanics. Although research on coordination and control of soccer skills is currently sparse, there are indications that the relationship between motor control and biomechanics could form a significant component of scientific programmes in talent identification and skill development. Further interdisciplinary work is needed to enhance understanding of coordination and control of soccer skills.     

The science and medicine of cricket: an overview and update

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.     

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.     

Use of deterministic models in sports and exercise biomechanics research

A deterministic model is a modeling paradigm that determines the relationships between a movement outcome measure and the biomechanical factors that produce such a measure. This review provides an overview of the use of deterministic models in biomechanics research, a historical summary of this research, and an analysis of the advantages and disadvantages of using deterministic models. The deterministic model approach has been utilized in technique analysis over the last three decades, especially in swimming, athletics field events, and gymnastics. In addition to their applications in sports and exercise biomechanics, deterministic models have been applied successfully in research on selected motor skills. The advantage of the deterministic model approach is that it helps to avoid selecting performance or injury variables arbitrarily and to provide the necessary theoretical basis for examining the relative importance of various factors that influence the outcome of a movement task. Several disadvantages of deterministic models, such as the use of subjective measures for the performance outcome, were discussed. It is recommended that exercise and sports biomechanics scholars should consider using deterministic models to help identify meaningful dependent variables in their studies.     

Use of deterministic models in sports and exercise biomechanics research

A deterministic model is a modeling paradigm that determines the relationships between a movement outcome measure and the biomechanical factors that produce such a measure. This review provides an overview of the use of deterministic models in biomechanics research, a historical summary of this research, and an analysis of the advantages and disadvantages of using deterministic models. The deterministic model approach has been utilized in technique analysis over the last three decades, especially in swimming, athletics field events, and gymnastics. In addition to their applications in sports and exercise biomechanics, deterministic models have been applied successfully in research on selected motor skills. The advantage of the deterministic model approach is that it helps to avoid selecting performance or injury variables arbitrarily and to provide the necessary theoretical basis for examining the relative importance of various factors that influence the outcome of a movement task. Several disadvantages of deterministic models, such as the use of subjective measures for the performance outcome, were discussed. It is recommended that exercise and sports biomechanics scholars should consider using deterministic models to help identify meaningful dependent variables in their studies.     

A systematic approach to analysing sports performance

A systematic approach to the analysis of sporting events is discussed. The basic tenet is that objective quantification of critical events is required for a complete analysis. This approach encompasses diverse areas of methodology and research, such as quantification, biomechanics and physiology. The theoretical underpinning are behavioural, in so far as athletes produce observable behaviour that can be quantified and ultimately changed. Several areas of analysis are linked together in a general framework and each one of these areas is dealt with in detail.     

Refining and regaining skills in fixation/diversification stage performers: the Five-A Model

Technical change is one of many factors underpinning success in elite, fixation/diversification stage performers. Surprisingly, however, there is a dearth of research pertaining to this process or the most efficacious methods used to bring about such a change. In this paper we highlight the emergent processes, yet also the lack in mechanistic comprehension surrounding technical change, addressing issues within the motor control, sport psychology, coaching and choking literature. More importantly, we seek an understanding of how these changes can be made more secure to competitive pressure, and how this can be embedded within the process of technical change. Following this review, we propose the Five-A Model based on successful coaching techniques, psychosocial concomitants, the avoidance of choking and principles of effective behaviour change. Specific mechanisms for each stage are discussed, with a focus on the use of holistic rhythm-based cues as a possible way of internalising changes. Finally, we suggest the need for further research to examine these five stages, to aid a more comprehensive construction of the content and delivery of such a programme within the applied setting.     

Evidence for biomechanics and motor learning research improving golf performance

The aim of this review was to determine how the findings of biomechanics and motor control/learning research may be used to improve golf performance. To be eligible, the biomechanics and motor learning studies had to use direct (ball displacement and shot accuracy) or indirect (clubhead velocity and clubface angle) golf performance outcome measures. Biomechanical studies suggested that reducing the radius path of the hands during the downswing, increasing wrist torque and/or range of motion, delaying wrist motion to late in the downswing, increasing downswing amplitude, improving sequential acceleration of body parts, improving weight transfer, and utilising X-factor stretch and physical conditioning programmes can improve clubhead velocity. Motor learning studies suggested that golf performance improved more when golfers focused on swing outcome or clubhead movement rather than specific body movements. A distributed practice approach involving multiple sessions per week of blocked, errorless practice may be best for improving putting accuracy of novice golfers, although variable practice may be better for skilled golfers. Video, verbal, or a combination of video and verbal feedback can increase mid-short iron distance in novice to mid-handicap (hcp) golfers. Coaches should not only continue to critique swing technique but also consider how the focus, structure, and types of feedback for practice may alter learning for different groups of golfers.     

A New Perspective on Motor Skill Automation

Abstract

The article by Richard A. Schmidt is directed to the locus of movement control. The paper's major goal is to describe a reconciliation between the peripheralists and the centralists. Schmidt describes major research issues for the future, along with current thinking about the central control of action in various theoretical conceptualizations of the structure of central motor programs. In the presentation on motor skill automation George E. Stelmach and Douglas D. Larish introduce the concept of attention and review research findings concerning attention, automation, and movement. They recommend automatic sequencing as a more viable theoretical position. Empirical support is given for the stance taken by these authors, followed by examples of potential approaches to research in motor behavior.     

Reviewing the Variability-Overuse Injury Hypothesis: Does Movement Variability Relate to Landing Injuries?

Purpose: Overuse injuries are common in sport, but complete understanding of injury risk factors remains incomplete. Although biomechanical studies frequently examine musculoskeletal injury mechanisms, human movement variability studies aim to better understand neuromotor functioning, with proposed connections between overuse injury mechanisms and changes in motor variability. Method: In a narrative review, we discuss the variability-overuse injury hypothesis, which suggests repeated load application leads to mechanical tissue breakdown and subsequent injury when exceeding the rate of physiological adaptation. Due to the multidisciplinary nature of this hypothesis, we incorporate concepts from motor control, neurophysiology, biomechanics, as well as research design and data analysis. We therefore summarize multiple perspectives while proposing theoretical relationships between movement variability and lower extremity overuse injuries. Results: Experimental data are presented and summarized from published experiments examining interactions between experimental task demands and movement variability in the context of drop landing movements, along with comparisons to previous movement variability studies. Conclusion: We provide a conceptual framework for sports medicine researchers interested in predicting and preventing sports injuries. Under performance conditions with greater task demands, we predict reduced trial-to-trial movement variability that could increase the likelihood of overuse injuries.     

Body Segment Contributions to Sport Skill Performance: Two Contrasting Approaches

Abstract

To lead off this section, Anne E. Atwater examines recent developments in kinesiology and biomechanics and discusses the appropriateness of distinguishing between these two areas. Atwater proceeds by tracing the development of the two areas, attempting to clarify the similarities and differences, and concludes by discussing new developments in technology and methodology, along with future directions for both kinesiology and biomechanics. The article by Doris I. Miller contrasts two methods for approaching the problems of body segment contributions to motor performance: joint immobilization with restraint and resultant muscle torque pattern. Miller indicates a preference for the second approach, but indicates that investigators face three major challenges when using it. The author completes the presentation with applications of this method to research on kicking and running.