Essentials of Exercise Physiology and Exercise Testing

Prof. J. Bourgois, Ph.D.

Centre of Sports Medicine, Medical Oncology, Dept. Rehabilitation Sciences and Physiotherapy, Ghent University Hospital and Ghent University, Belgium

Exercise can be categorised as maximal effort exercise, short-term exercise, long-term exercise and progressive incremental exercise until exhaustion. The power-duration curve gives highly relevant information of the maximal sustained power output of an individual in function of exercise duration during cycling. Within the power-duration curve, maximal power may shifted upward or downward according to the strength of the leg muscles. The shape of the curve is influenced by muscle fibre type and by training.

Knowing that there are different muscle fibre types (Type I or Slow Twitch Fibres, Type II a and II b or the Fast Twitch Fibres, and II c or undifferentiated fibres), we need to understand their significance and the role that they play in exercise. Type I are well suited to aerobic (with oxygen) endurance exercise (long-term exercise). Type II a and b, on the other hand , are better suited to perform anaerobically (without oxygen: maximal effort– and short-term exercise). Type II c, normally rare and undifferentiated, may contribute to reinnervation and motor unit transformation. The needle biopsy technique allows us to study muscle fibres and to recognise the effects of acute exercise and chronic training on their composition and metabolic characteristics. During most forms of movement, there appears to be an orderly hierarchy of motor unit recruitment. During light exercise mostly Type I fibres will be recruited, during moderate exercise both Type I and II a, and during more severe exercise all fibre types will contribute to force production.

Energy from the breakdown of ATP provides energy for all forms of biological function. Within the muscle, ATP is generated through 3 energy systems: regeneration during exercise through phosphocreatine (ATP and PCr: anaerobic alactic metabolism), the anaerobic metabolism of glucogen or glucose (glycolysis: anaerobic lactic metabolism) or the aerobic metabolism of acetyl-CoA derived principally from the breakdown of carbohydrates or lipid. The availability of extra-muscular fuel and of oxygen influences the metabolic response to exercise. Therefore, cardiovascular and pulmonary physiology is highly relevant to any consideration of muscle metabolism during exercise. The percentage contributions of the aerobic and anaerobic energy transfer depend largely on exercise intensity and duration. A number of factors are known to influence the selection of fuel for exercise, and there can be significant interactions between several of them. Evaluation of the immediate (ATP-PCr), the short-term (glycolysis) and the long-term (aerobics) energy system can give interesting information of an individual’s bioenergetics. The capacity for each form of energy transfer varies considerably among individuals. Performance and capacity test, as well as appropriate physiological measurements, evaluate energy-transfer capacity of the different energy systems.

Children and adolescents are not mini-adults. The physiological characteristics and the response to exercise in children and adolescents are different from those of adults:

physical

pulmonary

cardiovascular

metabolic

hormonal

thermoregulatory

During growth and maturation, these differences become more similar to the adult’s characteristics and responses to exercise. The knowledge and the understanding of these differences between children/adolescents and adults are of major and practical importance to scientists, physicians, paramedics,… working with children and adolescents.