Indoor Sport Services Training Guide

Whilst we all know that it will happen it is, never the less, a shock when puberty arrives, not just for the adolescent but also those around them. For this reason it is important for the coach or adult responsible for training that they understand the physiological changes that take place and are able to construct the training programme appropriately.

Growth Spurt

The adolescent growth spurt through puberty may increase height by up to 6? (15cm) or more. The spurt starts between 10 and 12 in girls, 12 and 14 in boys (but may start earlier or later in both). For a while girls may be bigger and stronger than their male peers. Before puberty 66% of growth is in legs; after, 60% is in trunk. Early maturers do well in age-group sport but may drop out later, as others catch them up.

Bones

After the growth spurt, girls have a broader pelvis, boys have broader shoulder girdles and longer arms - all relative to body size. The valgus angle (angle in elbow) in girls may interfere with throwing, and it makes the elbow susceptible to injury, e.g. javelin throwing.

Body Fat

Until the growth spurt, both sexes are fairly equal at about 16-18% body fat, then the boys lose fat to about 12-15% through adolescence and the girls gain it to about 21-25%, by 17. This fat difference penalises the girls in many sports, but may be an advantage in some swimming events.

Cardio-respiratory

Maximal adult heart rates tend to be around 200 bpm, but children may reach 20-25 beats higher, at lower blood pressures. Children have relatively higher respiratory rates than adults, and their Ventilatory Equivalent (VE) for oxygen is higher. The VE is the volume of air ventilated to give an oxygen intake of one litre. At 8 years old the VE may be 38 litres of air per litre of oxygen; by 18, this will have dropped to 28 litres. In young children this may predispose to hypocapnia, (a decreased level of carbon dioxide in the blood) with flexor spasms of hands and feet; treat by rebreathing via a paper bag.

Aerobic Power

Children are biomechanically and biochemically ?wasteful? of energy (as indicated by their higher VE). The oxygen costs of running and walking are relatively higher in children than in adults. For example, at 10km/hr the oxygen cost may be 47ml/kg at age of six, but only 38ml/kg at 17. In cycling, the energy costs are closer between younger and older children, as the mechanics of the cycle tend to even out the biomechanical differences.

Anaerobic Power

Even when normalised for body mass, the anaerobic energy produced by an 8-year old is about 70% of that at age 11, which in turn is less than a 14-year old. Children?s muscle contains less glycogen, it is utilised at a lower rate, and lower levels of lactic acid are produced. Thus young children don?t have the lactate fatigue barrier of adults.

Strength

With respect to strength, muscle forms a much lower percentage of body mass before puberty - e.g. 27% compared to 36-44%. Strength training, especially in boys, is more effective after puberty.

Thermoregulation

An 8-year old may have a body surface area/body mass ratio nearly 40% greater than an adult. This can lead to greater rates of heat absorption in the sun, or of heat loss in cold water. Sweat rates before puberty may be around 350-450ml/m2/hour compared to between 600-800ml/m2/hour after puberty.

Voluntary Dehydration

Especially in children, thirst tends not to match water loss over a few hours, as in exercise and sporting situations. Drink stops should be programmed.

Exercise Perception

At equivalent levels, children perceived exercise as being much easier than adults. Thus it is easy to overwork children in sports training situations.