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INTRODUCTION

Physiology is the study of how the body functions: how individual cells, tissues and organs work in isolation and how they interact in a coherent way in the whole living organism. An understanding of physiology is of central importance in medicine and all of the related health sciences, including nutrition. It is also important to recognise that the modern science of biochemistry—and all its offshoots, including molecular biology and the various omics technologies—grew from physiology. Biochemistry, the chemistry of life, which is fundamental to nutrition and metabolism, developed as an offshoot of physiological chemistry, the chemistry of processes occurring in living animals. The scope of physiology ranges from understanding events at the molecular level (e.g. how muscles contract or how cells sense nutrients) to the integrative physiology of organs and systems (e.g. the brain and the cardiovascular and respiratory systems) and how they are regulated and adjust to stress or change (e.g. in response to exercise or to environmental extremes such as the microgravity of space flight). The emphasis of physiology is on the integration of molecular, cellular, system and whole-body function. Understanding normal function allows prediction of how the organism will respond to any stimulus or stress that is applied.

Exercise physiology is the study of how the body functions in response to the challenge of exercise. Again, this includes the study of how cells, tissues and organs work, but specifically in preparation for exercise, during exercise and in the recovery period after exercise. Research in the field of exercise physiology has led to understanding in a wide range of topics related to sport and exercise nutrition. The physiology of sports performance is built on the foundation of exercise physiology and includes the study of elite athletes in an effort to understand the physiological characteristics that contribute to successful performance in different sports, and the various factors, including training and nutrition, that can modify these characteristics and so determine performance in various types of sports activities. Exercise physiology also includes the study of various clinical populations; such studies can shed light on how malfunction of various organs may limit the ability to perform exercise.

HOMEOSTASIS

Homeostasis refers to the maintenance of a relatively constant internal environment of the body. It is the central feature of the body’s physiological processes. These processes aim to reverse any imposed change and so maintain a constant internal environment. The existence of these mechanisms allows the human body to cope with conditions far beyond those that are normally encountered; typically, we use only a small part of our functional capabilities in normal day-to-day activities. A bout of hard exercise is one of the biggest threats to this homeostasis that the healthy individual is likely to encounter. Exercise, if it is sufficiently severe and prolonged, will result in changes to the partial pressure of oxygen in the tissues, blood volume and blood pressure, temperature, acid-base ...

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