Key Concepts in Sport and Exercise Sciences

David Kirk, Carlton Cooke, Anne Flintoff, Jim McKenna, David Kirk, Carlton Cooke, Anne Flintoff, Jim McKenna

• Editorial: SAGE Publications Ltd
• Año: 2008
• ISBN:
  9781446243572
• Edición: 1
• Categoría: Education
• Categoría: Adult Education

?A very useful introduction to the key concepts in five main areas of study in sport and exercise science. The multi-disciplinary nature of the book is particularly attractive as it means that it can be used to support students studying a range of sport and exercise courses and modules. Furthermore, the chapters are concise, informative, written in an accessible style, and provide a good balance between theory and application to practice, making it a very interesting and relevant read? - Dr Lorraine Cale, Loughborough University

This book provides students and scholars with a fail-safe guide to the key concepts in the field of Sport & Exercise Science. Intelligently cross-referenced entries provide a sound map of the multi-disciplinary demands of sport related courses including physical and biological sciences, social science and education. The entries use clear definitions, examples and suggestions for further reading to explore each discipline and are:

"Comprehensive

"Lucid

"Pertinent to study needs

"Practically relevant

David Kirk is Professor in Physical Education and Youth Sport

Carlton Cooke is Professor in Physical Education

Anne Flintoff is Reader in Physical Education

Jim McKenna is Professor in Physical Activity and Health

All at the Carnegie Faculty of Sport and Education, Leeds Metropolitan University.

PART I

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Biomechanics

INTRODUCTION

Biomechanics is the area of sport and exercise science where the laws, principles and methods of mechanics are applied to the structure and function of the human body. Mechanics can be divided into two categories: statics, which is the study of stationary objects, and dynamics, which is the study of moving objects. Examples of static analysis in sport include standing, different balances in gymnastics and acrobatics and certain resistance exercises where no movement is apparent but large forces may be exerted such as in a scrum in rugby or a closely matched tug-of-war contest. Most activities in physical activity and sport involve movement and therefore require the application of dynamics to understand that movement.

Two other subdivisions are often used to describe different levels of biomechanical analysis: Kinematics, which is a description of the movement in terms of time and space, and kinetics, which is concerned with an explanation of the underlying mechanics of the movement and typically involves an assessment of forces. Kinematic analyses in sport typically rely on images recorded by video and other cameras, which can be played back many times either at normal speed or frame by frame, pausing on key frames that show important aspects of the technique. Kinetic analyses in sport and exercise also employ images, but supplement these with force plates and other force transducers, that allow the forces exerted against the ground or on sports equipment to be measured. An example of kinetic analysis related to health is gait analysis, which typically combines ground reaction force data captured as an individual steps on and off a force plate synchronised with frame-by-frame images recorded by a camera. Such an analysis may help a podiatrist to diagnose the cause of problems in walking, where the data collected can assist in prescribing orthotics, which are inserts to go into shoes to help alleviate problems in walking. A typical example from sport would also combine frame-by-frame images synchronised with force measurements, such as the video recording of a kayak paddling stroke, while simultaneously recording the magnitude and direction of the forces exerted on the shaft of the paddle.

The following entries introduce the different components of biomechanics and will help students gain a good understanding of how to analyse movement and learn how to explain how it is produced. The ability to separate good and bad elements of the mechanics of techniques and style is a requirement for all biomechanists who wish to be able to explain how movement patterns in physical activity and sport can be improved.

CARLTON COOKE

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Kinematics

Video analysis has become a very popular method to assess sports performance. The recording and repeated observation of motion captured by video cameras is relatively straightforward, especially now that the technology is so readily available and feedback on what has been recorded is immediate via playback through the camera.

However, there are different approaches to motion analysis, which are characterised by the principles and methodology underpinning them. Qualitative analysis (non-numerical and descriptive) is based entirely on visual observation of a movement, sequence of movements or a game performance and it draws its validity from the knowledge and experience of the person who observes and analyses the selected motion. In contrast a quantitative approach (numerical analysis) guarantees objective results as long as the correct mechanical principles and scientific methodology are used. The branch of Biomechanics that describes human or object motion mainly via image analysis is called kinematics. Kinematics describes motion in terms of space and time, and it provides valuable information regarding the position and the rate of movement of the human body, its segments or any implement used in a sport and exercise situation.

TYPES OF MOTION AND MECHANICAL QUANTITIES

The pathway of the motion experienced by moving bodies can be described as either straight line (rectilinear motion), or curved line (curvilinear motion) or they can rotate about an axis (angular motion). For example, an ice hockey player gliding straight across the ice with the same posture will result in all the segments of his body moving the same distance over the same time period (translation). In addition a discus travelling in the air following a curved path is an example of linear motion since its motion is translational too. In contrast, a gymnast who rotates around the high bar with a straight body position undergoes rotation about an external fixed axis where all the body segments travel through the same angle, in the same direction, in the same time, but covering different curvilinear distances with the segments further away from the axis (e.g. feet) travelling further than the segments closer to the axis (e.g. shoulders). There are also occasions where angular motion is observed with respect to an imaginary axis, which in many events could be located outside the physical boundaries of the human body (e.g. rotations in gymnastics or diving about the centre of gravity during flight). However, the most common form of motion in sport and exercise is a combination of angular and linear motion; this is called general motion. For instance in cycling, some body segments (e.g. thighs and legs) and parts of the bicycle (wheels) undergo rotation about joints of the body and the centre of the wheel respectively, whereas other body segments (e.g. hips and head) and bicycle parts (e.g. bicycle frame) undergo translation with the total movement of the system (bicycle and cyclist) being linear.

Once the type of motion has been established the kinematic analysis can be performed by applying mechanical principles and formulae that provide information about the changes in the distance covered, the speed of movement and temporal pattern of the movement. In other words, by using vector quantities (magnitude and direction) instead of scalar (magnitude), the position displacement, velocity and acceleration of a body and/or object can be measured and expressed in S.I. units by using the same techniques and formulae for both angular and linear kinematics. The names, symbols and specific units differ between linear and angular quantities to allow inclusion of the characteristics of each type of motion. For example, the definition of velocity is the rate at which a body changes its position with respect to time and it can be obtained if the change in displacement is divided by the time taken for the change in displacement. In linear motion this velocity is denoted by the Latin letter v and it is measured in m.s^-1. In angular motion it is denoted by the Greek letter ω and it is measured in rad.s^-1since the change in angular position is represented by the change in angle measured in radians (radians are used because they provide a means of calculating linear velocity of any point rotating around an axis by using the equation v=ω r, where v is linear velocity (m.s^-1), ω is angular velocity (rad.s^-1) and r is the radius (m). There are 2π radians in 360^o).

ANALYSING MOVEMENT IN PHYSICAL ACTIVITY AND SPORT

One of the main uses of biomechanics in sport and exercise science is in the analysis of patterns of human movement in either physical activity or sport. General movement patterns have common elements in terms of segment movements, axes of rotation and planes of movement and are easily recognised by most people and described as walking, running, jumping, throwing, catching, striking and kicking. When a general movement pattern is adapted for use in a particular physical activity or sport it is a skill. Taking the example of jumping, the high jump would be a particular skill within the general group of movement patterns we would all recognise as jumps. There are of course different ways of performing the high jump, with most children starting with a scissor jump and most, if not all, international high jumpers performing the Fosbury flop (named after its originator, high jumper Dick Fosbury). Different ways of performing a skill are called techniques, so that the scissor jump and Fosbury flop represent examples of very different high jump techniques. Each of these techniques would have common elements, which make them relatively easy for us to categorise as particular forms of high jump technique. However, if you watch international high jumpers performing the Fosbury flop, you will observe that not all jumpers execute the Fosbury flop in exactly the same way. Rather, they have adapted or modified the technique; and these individual differences and adaptations are known as the style of the performer. Skill, technique and style are developed as a function of the requirements and constraints of a particular event such as the high jump (e.g. the rules of high jumping that require a one-leg take-off; the shape of the high jump area, which allows for a curved approach; the size, shape and fitness of the jumper, which are human constraints; and the coach, who may develop the Fosbury flop with an emphasis on certain aspects of the technique).

APPLICATIONS OF KINEMATICS

There is a wide spectrum of applications of linear and angular kinematics in sport and exercise. These applications are extremely valuable in motion analysis, especially now that advanced technology has improved the equipment that is used to obtain kinematic data. The employment of high-speed video systems in conjunction with sophisticated software, which converts the captured images into two- and three-dimensional coordinates, enables the sports biomechanist to obtain accurate estimates of instantaneous values of the kinematic variables critical in the performance of a movement or sequence of movements. The calculation of instantaneous rather than average values of a given quantity (e.g. velocity) distinguishes quantitative kinematic analysis from qualitative observation. In most analyses of sport it is much more informative to determine the characteristics of a performance at a particular instant in time. For instance, the linear velocities of the centre of gravity and its projection angle with respect to the horizontal at the instant of take-off in long jump will determine to a large extent the distance jumped by the athlete. There are numerous examples of the use of kinematic analyses right across the range of sport and exercise performances. On many occasions the use of kinematic analysis is significant in examining sporting movements that rely extensively on the performance of correct and effective technique, such as in a tennis serve or a javelin throw. Data from a kinematic analysis of these two movements can provide the coach and the performer with valuable information on technique, but also inform recommendations with respect to corrections and adjustments that can lead to performance enhancement. Kinematic analysis has also proved successful in health-related applications, especially those that examine the effects of body posture and the specific movement patterns on the musculoskeletal system during different sport and recreational activities. The outcome of these applications is typically:

1. identification of the source of a problem affecting the performer (e.g. overpronation in running)
2. measures and advice on how to reduce or prevent the problem which, in running for example, might include a change of footwear or the prescription of an orthotic insert by a podiatrist.

When analysing movement a sound understanding of the laws, principles and methods of biomechanics can enable students to observe and explain which elements of technique and style are effective in optimising the movement and which need to be changed to produce a better movement pattern, either in terms of performance or prevention of injury. For example, a discus thrower who leans backwards as she makes the first turn at the back of the circle, will most probably translate that backward lean to the throwing position at the front of the circle. This will result in a loss of power and therefore velocity at the point of release. For a right-handed thrower leaning back through the delivery phase, the point of release will occur too soon and the discus will land towards the right line of the sector or, worse still, hit the cage or go out of the sector, producing a foul throw. An explanation of such errors in style and technique can only be made with good observational skills coupled with the application of biomechanics.

FURTHER READING

Hamill, J. and Knutzen, K.M. (2003) Biomechanical Basis of Human Movement, 2nd edn. Philadelphia, PA: Lippincott, Williams & Wilkins.

Watkins, J. (2007) Introduction to Biomechanics of Sport and Exercise. Oxford: Elsevier Health Sciences.

Zatsiorsky, V. (1998) Kinematics of Human Motion. Champaign, IL: Human Kinetics.

NASSOS BISSAS CARLTON COOKE

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Force

KINETICS

Understanding force is essential to understanding movement, not just in a sporting context but also in everyday activities. While kinematics is about describing movement and kinetics is about explaining cause and effect in movement, unde...