The American College of Sports Medicine developed an opinion statement on the amount of physical activity needed for optimal functional capacity and health. They proposed that children and adolescents should obtain 20–30 min of vigorous exercise each day. In the beginning of the 1990s this recommendation was refined by the International Consensus Conference on Physical Activity Guidelines for Adolescents (Sallis & Patrick 1994), in which new physical activity guidelines for adolescents were developed.
The expert committee, with researchers from the USA, Canada, Europe and Australia, decided not to develop guidelines for children’s physical activity, because of a lack of scientific evidence in the younger age groups.
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Although it is not the intention to review the many combinations and permutations that can arise by manipulating the components of a resistance training programme, this section will highlight some of the main points that have some scientific foundation within the literature.
As it is not within the scope of this chapter to identify all of the research studies and groups who have reported their findings in the literature, the following section highlights some of the major results that have been presented by Faigenbaum and his associates over the last 12 years. A search of the literature using any of the computer-based search engines will provide further details of the individual studies by Faigenbaum and his colleagues.
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Lactate is continuously produced in skeletal muscle, even at rest, but with the onset of exercise, increases in the glycolytic resynthesis of ATP result in a correspondingly greater production of lactate in active fibres.
Lactate metabolism is a dynamic process and while some fibres produce lactate, adjacent fibres simultaneously consume it as an energy source. Nevertheless, during exercise lactate accumulates within the muscle and, although output does not match production, some lactate will diffuse into the blood where, during submaximal exercise, it can be sampled, assayed and analysed to provide an estimate of the anaerobic contribution to exercise and therefore a measure of aerobic fitness.
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Aerobic fitness may be defined as the ability to deliver oxygen to the exercising muscles and to utilize it to generate energy during exercise. Aerobic fitness therefore depends upon the pulmonary, cardiovascular and haematological components of oxygen delivery and the oxidative mechanisms of the exercising muscle.
Maximal oxygen uptake (VO2max), the highest rate at which an individual can consume oxygen during exercise, is widely recognized as the best single measure of adults’ aerobic fitness. Maximal oxygen uptake conventionally implies the existence
of a VO2 plateau but this response is not typical of children and adolescents and it has gradually become more common to use the term peak VO2, the highest VO2 elicited during an exercise test to exhaustion, to describe young people’s aerobic
fitness.
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The work required to inflate and deflate the lung is governed by the equation: work = total intrapleural pressure × change in lung volume. For a given lung volume, it is therefore the internal pressures opposing inflation and deflation that dictate the efficiency of the lung.
Three main components contribute to intrapleural pressure other than the active contraction of the diaphragm and respiratory muscles: airway resistance, respiratory system compliance and elastic recoil. Each of these components change with growth, and have important implications with regard to ventilatory patterns in children.
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