Fundamental Biomechanics of Sport and Exercise

James Watkins

• Publisher: Routledge
• Year: 2014
• ISBN:
  9781135074951
• Edition: 1
• Topic: Medicine
• Subtopic: Sports Medicine

Fundamental Biomechanics of Sport and Exercise is an engaging and comprehensive introductory textbook that explains biomechanical concepts from first principles, showing clearly how the science relates to real sport and exercise situations.

The book is divided into two parts. The first provides a clear and detailed introduction to the structure and function of the human musculoskeletal system and its structural adaptations, essential for a thorough understanding of human movement. The second part focuses on the biomechanics of movement, describing the forces that act on the human body and the effects of those forces on the movement of the body.

Every chapter includes numerous applied examples from sport and exercise, helping the student to understand how mechanical concepts describe both simple and complex movements, from running and jumping to pole-vaulting or kicking a football. In addition, innovative worksheets for field and laboratory work are included that contain clear objectives, a description of method, data recording sheets, plus a set of exemplary data and worked analysis. Alongside these useful features are definitions of key terms plus review questions to aid student learning, with detailed solutions provided for all numerical questions.

No other textbook offers such a clear, easy-to-understand introduction to the fundamentals of biomechanics. This is an essential textbook for any biomechanics course taken as part of degree programme in sport and exercise science, kinesiology, physical therapy, sports coaching or athletic training.

Part I

---

Functional anatomy of the musculoskeletal system

The open-chain arrangement of the bones of the skeleton – two arms and two legs attached independently to the vertebral column – allows us to adopt a wide range of body postures and perform a wide range of movements. However, this movement capability is only possible at the expense of low mechanical advantage of skeletal muscles, such that in most postures and movements other than lying down, the muscles have to exert very large forces, which, in turn, result in very large forces in bones and joints. The musculoskeletal components normally adapt their size, shape and structure, a process referred to as structural adaptation, to more readily withstand the time-averaged forces exerted on them in everyday physical activity. Structural adaptation is continuous throughout life, but the capacity for structural adaptation decreases with age after maturity. Consequently, there is an intimate relationship between the structure and functions of the components of the musculoskeletal system. Part I describes how musculoskeletal function – the generation and transmission of forces to control the movement of the body – is reflected in the structure of the musculoskeletal components.

Chapter 1 – The musculoskeletal system – describes the composition and function of the musculoskeletal system. Chapter 2 – The skeleton – describes the bones of the skeleton and, in particular, the features of the bones associated with force transmission at joints. Chapter 3 – Connective tissues – describes the ordinary connective tissues, in particular, ligaments, tendons and fascia, and the special connective tissues of cartilage and bone. Chapter 4 – The articular system – describes the joints and, in particular, the way joint design reflects a trade-off between stability and flexibility. Chapter 5 – The neuromuscu-lar system – describes the interaction between the nervous and muscular systems in the control of joint movements. Chapter 6 – Mechanical characteristics of musculoskeletal components – describes the response of the musculoskeletal components to the forces exerted on them during everyday activity. Chapter 7 – Structural adaptation – describes how the musculoskeletal components adapt to the time-averaged forces exerted on them.

Chapter 1

---

The musculoskeletal system

All living organisms are made up of cells. The human body is made up of billions of cells, which are organised into complex groups that carry out specific functions. These groups include the cardiovascular system, which transports blood around the body, and the musculoskeletal system, which enables us to move. The first part of this chapter describes the four fundamental types of cell in the body and the organisation of the cells within functional groups. The second part of the chapter describes the composition and structure of the musculoskeletal system.

OBJECTIVES

After reading this chapter, you should be able to do the following:

1. Describe the four types of tissue.

2. Describe cellular organisation in multicellular organisms.

3. Describe the composition and function of the musculoskeletal system.

UNICELLULAR AND MULTICELLULAR ORGANISMS

The fundamental structural and functional unit of all living organisms is the cell. The lowest forms of life consist entirely of single cells and are referred to as unicellular organisms. Higher forms of life, like the human body, consist of many cells and are referred to as multicellular organisms.

There are two general categories of cells, prokaryotes and eukaryotes (Alberts et al. 2002). A prokaryotic cell consists of an outer cell membrane (comprised of proteins and lipids) that encloses a semitransparent fluid called cytosol (a complex solution of proteins, salts and sugars). The cell membrane, usually referred to as the plasma membrane or plasmalemma, separates and protects the cell from its surrounding environment and allows interchange of substances between the cytosol and the surrounding environment via a system of channels and pumps.

Eukaryotes are similar to prokaryotes in that they have a cell membrane that encloses cytosol. However, whereas the cytosol of a prokaryotic cell is largely featureless, the cytosol of a eukaryotic cell surrounds a number of distinct structures, which differ in size and shape (Figure 1.1). The most distinct of these structures is the nucleus, which contains the cell’s genetic material (23 pairs of chromosomes in human beings). The other structures are called organelles; these include lysosomes (involved in digestion of nutrients), mitochondria (production of energy), ribosomes (assembly of amino acids into proteins), and centrioles (involved in cell division). The nucleus organises and controls, via the organelles, the life processes of the cell. The life processes include growth and development, respiration, circulation, digestion, excretion, reproduction and movement. In prokaryotes the genetic material is distributed throughout the cytosol and the life processes are carried out by indistinct structures in the cell membrane.

Figure 1.1 Section through a generalised eukaryotic cell.

All prokaryotic organisms, which include bacteria, are unicellular. Eukaryotic organisms range from unicellular organisms, such as amoeba and euglena, to multicellular organisms, such as the human body. All mammals, birds and fish are multicellular organisms. The number of cells in multicellular organisms varies considerably. For example, the nematode worm Caenorhabditis elegans is 1 mm (millimetre) in length and consists of 959 cells (Kenyon 1988). Most multicellular organisms consist of millions of cells; the human body consists of approximately 10¹⁴ (one hundred million million) cells (Alberts et al. 2002).

The fundamental structural and functional unit of living organisms is the cell. A unicellular organism consists entirely of a single cell. A multicellular organism consists of many cells.

Like cytosol, the cell membrane consists of a viscous fluid, but it is usually much more viscous than the cytosol. The viscous (capacity to change shape in response to an applied force) nature of the cell membrane and cytosol enables a cell to change its shape without losing its integrity. During normal functioning, many cells regularly change shape and the amount of change depends on the type of cell. For example, in muscle cells the ability to change shape is highly specialised and is an essential feature of normal function. Muscle cells are long and thin and may shorten by up to 40% during contraction (production of a pulling force). In contrast, bone cells occupy tiny spaces within a fairly hard bony matrix, such that change in shape of bone cells is minimal during normal everyday activity.

The structure of a cell determines its function. Whereas muscle cells and bone cells are both eukaryotic, they have different functions and, as such, are different in structure. The human body is made up of four fundamental types of eukaryotic cells, called tissues.

CELLULAR ORGANISATION IN MULTICELLULAR ORGANISMS

All living organisms carry out all of the essential life processes. In unicellular organisms the life processes are, in biological terms, relatively simple. However, in multicellular organisms the cells are organised into complex functional groups that carry out the various life processes for the organism as a whole. There are three levels of cellular organisation in each functional group: tissues, organs and systems.

Tissues

In multicellular organisms all of the cells originate from a single cell formed by the fertilisation of a female ovum by a male sperm. This cell undergoes rapid cell division to form a large number of similar cells. Soon after this, the cells differentiate in size, shape and structure, in order to carry out different functions within the developing organism (Wozniak and Chen 2009). This process of cellular differentiation results in the formation of four types of cells called tissues: epithelia, nerve, muscle and connective. A tissue is a group of cells having the same specialised structure, so as to perform a particular function in the body (Freeman and Bracegirdle 1967). The word tissue is also used in a general sense, such as in the description of skin, muscles, tendons, ligaments and fat as soft tissues.

Epithelial tissue

There are two types of epithelial tissue: covering and glandular. Covering epithelia form the surface layers of cells of all the internal and external free surfaces of the body except the surfaces inside synovial joints. For example, the surfaces of the skin and the lining of the alimentary canal, heart chambers and blood vessels are all examples of covering epithelia.

All cells secrete fluid to a certain extent, but glandular epithelial cells are specialised for this purpose and form the two types of glands: exocrine and endocrine. Many of the exocrine glands (glands with ducts that discharge secretions onto a surface), such as the gastric glands in the lining of the stomach, secrete fluids containing enzymes necessary for the digestion of food. Endocrine glands (ductless glands that discharge secretions directly into the blood stream), such as the pituitary gland at the base of the brain and the adrenal glands at the upper end of each kidney, secrete hormones that, in association with the nervous system, regulate and coordinate the various body functions.

Nerve tissue

Nerve cells (neurons) are specialised to conduct electroc...