THE YOUNG ATHLETE

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and maturation. 4. Issues of quantifying the training load in relation to establishing a dose-response pattern remain unresolved. 5. For ethical reasons measurements must be non-invasive and therefore determining the mechanisms of the adaptations remains limited.

11 12 age, years Figure 3: Peak oxygen uptake by boys and girls (reproduced from Winsley RJ, 1997)

14% at 6 years increasing to 25% by 17 years. Greater muscle mass and lower body fat is considered to be an important advan- tage for boys compared to girls. This is because the involvement of a greater amount of muscle mass will enhance per- formance whilst the additional increase in fat mass for girls must be carried during weight bearing activities eg. running and will decrease mechanical efficiency.

Boys who are mature for their chronologi- cal age are on average taller, heavier and have higher weight-to-height ratios than those boys who are late maturers. Also early maturing boys gain advantages in increased shoulder breadth and upper body muscle mass. These body changes are asso- ciated with increases in strength and power. These changes in muscle strength and power also translate to increases in aerobic power that further enhance sports performance. Girls who are early maturers are also taller, heavier with greater weight- to-height ratios than their same aged female peers. Early female maturers also have broader hips and shorter legs, which are associated with increased body fatness and can be disadvantageous in some sports. Interestingly, late maturing girls exhibit more linear physiques, less weight- to-height ratio, less fatness, relatively longer legs and lower hip-to-shoulder ratios, traits indicative of successful sport- ing performance. However, even though the physiological differences associated with maturity are less pronounced in girls than boys, it is not usual for early matur- ing girls to dominate female sport.

TEMPERATURE REGULATION The physiological differences between chil- dren, adolescents and adults are particular- ly pertinent when temperature regulation

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is considered. Significant differences in body size and surface area create problems and disadvantage young children in the heat and the cold. Due to the larger surface area to body mass ratio, children will absorb heat quicker than adults, as well as losing heat during colder environments. When children gain heat more quickly than adults, they are further disadvantaged by a lower sweating rate compared to adults. This is partly because children have a delayed sweating mechanism, as a higher core body temperature needs to be reached before sweating commences. Therefore, children are more reliant on conductive cooling to lose heat and less on evapora- tive sweating mechanisms. Children may be more at risk from heat related injuries in humid conditions and coaches should ensure adequate rest periods and fluids. There is still more that needs to be investigated regarding temperature regula- tion, as the published literature is, at present confined to no more than 18 papers (9). There is some suggestion of a maturity effect regarding the sweating response, but like many other studies a lack of control of other confounding variables makes conclusions tentative.

TRAINING Influences of training The evidence to support the proposition that children are as trainable as adults is equivocal. This is due to a number of confounding variables: 1. Many studies have not measured or monitored maturity status and hence children in the training study start at different maturity stages. 2. Many studies are too short and contain too few participants to be statistically valid. 3. The training adaptations are difficult to differentiate from the effects of growth

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Despite these confounding factors, there is an increasing opinion that children and adolescents are perhaps as trainable as adults, especially in relative percentage terms, but more research is required in this area.

Aerobic or endurance type training Young athletes have a greater cardiac function than their sedentary peers with a larger heart volume and chamber size compared to non-athletic children. Although there is some concern about children and endurance exercise, a number of studies have found no adverse effect of intense endurance training on the heart of the child athlete. In one study the echocardiography of a group of 9-14 year old boys involved in a 4 km road race, showed no evidence of changes in left ventricular contractility (10). Based on the limited data there does not appear to be any indication that intense training of the child athlete injures the heart, but clearly more studies of a longitudinal nature and with more sports is warranted.

Training studies designed to increase aerobic power have generally shown that children are able to improve their aerobic power by ~5-10 % relative to body mass. This is similar to adult training studies (11). Interestingly, most of the studies conducted that examined the aerobic trainability of children have been conduct- ed on children aged 8-11 years. There are considerably fewer studies from 13 years onwards which is when the increase in sports specialisation training often occurs (12). As many cross sectional and longitu- dinal studies have only involved school children and adolescents who are perhaps not genetically predisposed to elite sporting performance and have imposed the minimal level of training stimuli, it should be no surprise that the resulting adaptations are minimal. Coaches working with elite child athletes under a more rigorous training schedule in an academy or national squad, would be able to monitor and record more impressive

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