THE YOUNG ATHLETE KEY POINT

The timing (often referenced to chronological age) and tempo (rate of growth) of the maturation process will vary considerably relative to an individual’s CA.

25 cm of growth is observed. During the next year approximately 12 cm per year occurs and in the following year it is on average 6 cm per year. From three years of age onwards the rate of height increase is about 3-4 cm per year. The second highest growth rate experienced by an individual is during the adolescent growth spurt when a child enters puberty. The timing of this onset of growth is earlier for girls between 8.5-10.3 years compared to boys 10.3-12.1 years (Figure 1).

On average a boy will attain his highest growth rate in height between 13.4-14.4 years of age when he can expect to grow by 9 cm in that year, whilst a girl will experi- ence her highest growth rate approximate- ly two years earlier at 11.4-12.2 years and increase in height by 8 cm per year. Around this time most other parameters connected to general body size (body mass, heart size etc) will also be increasing at their maximal rates. This pattern of growth is well docu- mented through numerous longitudinal studies and forms the basis of percentile growth charts for children in the UK.

Maturation Biological maturation also follows a unique pattern and similarly is not linked to a chronological time frame. Hence in a class of children there will be a range of biolog- ically mature and immature children for the same chronological age. There are three main methods to assess maturity by: 1. Somatic (body dimensions) growth 2. Skeletal age 3. Secondary sexual characteristics.

Somatic growth The first assessment of biological maturity relates to predicting age at peak height velocity (PHV). The age at PHV can indi- cate maturity but serial measurements of height must be collected prior to and after the peak rate of growth and has been limited to longitudinal growth studies. More recently, a Canadian study (3) has led to the development of specific multiple regression equations based on chronologi- cal age, body mass, height, trunk length

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TABLE 1 GLOSSARY OF TERMS ■ Adulthood refers to the full maturation of all biological systems. Typically represented as 18 years and older by law.

■ Childhood is defined as the period from the first birthday to the beginning of puberty.

■ Chronological age refers to the number of years and days elapsed since birth. ■ Development refers to the interrelationship between growth and maturation in relation to the passage of time. The concept of development also includes the social, emotional, intellectual and motor realms of the child.

■ Growth refers to observable step-by-step changes in quantity, measurable changes in body size, for example, height, weight and fatness.

■ Infancy refers to the first year of life. ■ Maturation refers to qualitative system changes, both structural and functional in nature, in the organism’s progress toward maturity, for example, the change of car- tilage to bone in the skeleton.

■ Puberty refers to the somatic and physiological changes in children as the gonads change to the adult state. Puberty is not normally completed until the person is capable of producing a child. In England, puberty is recognised in law as 12 years for girls and 14 years for boys.

■ Skeletal age refers to the maturity of the skeleton determined by the degree of ossification of the bone structure.

■ Trainability refers to the responsiveness of developing individuals at different stages of growth and maturation to the training stimulus.

and leg length measures which eliminate the need for yearly measurements. This equation has been used to predict the age from PHV within ± 1 year in 95% of cases. Therefore it is quick, cheap and easy to use and can be used in cross sectional studies.

Skeletal age The second assessment of maturity is the estimation of the skeletal age. This requires an X-ray of the hand and wrist, although occasionally the knee is used. The principle of this method is that an individual more advanced in maturity will have greater bone development and a smaller amount of cartilage than a less mature person. In a group of 13 and 14 year olds, skeletal ages from 9 to 16 years have been found, demonstrating the wide variation of skeletal maturity for the same age (4). There are also concerns about whether the X-ray of the hand and wrist can accurately reflect the whole skeleton, as discrepancies of one year or more have been found between X-rays of the knee and the hand/wrist (5). However, the method is considered to be the best index of maturation but it is costly, involves a radiation dose to the individual and does require specialised equipment and trained personnel for interpretation.

Secondary sexual characteristics The final assessment is the rating of the secondary sex characteristics, a method devised by a paediatrician, James Tanner.

Tanner was responsible for conducting the classic longitudinal growth studies in the UK called the Harpenden Growth Study 1948-1971, on which much of this coun- try’s data on child growth is based. Tanner developed the characterisation of the secondary sex characteristics from earlier investigations by Reynolds and Wines in the 1950s. In brief, the breast develop- ment in girls, genitalia development in boys and pubic hair development in both sexes are categorised into five stages, as all follow a known pattern of development. These secondary sex stages are commonly known as Tanner stages. The ratings must be made by visual inspection, which is more easily accomplished in a clinical setting than a sporting one and can lead to some adolescents and parents feeling uncomfortable with this procedure. This uneasiness has led some investigators to use self-assessment methods whereby children or adolescents rate their sexual development from standardised drawings or photographs. However, there are concerns over the ability of individuals to accurately evaluate and self rate the five stages (6). Age at menarche is sometimes used as an indicator of maturity but the time when menarche occurs is relatively late compared to other somatic measures. Menarche typically occurs in non-athletes between 12.1-13.5 years with the suggestion that athletic girls experience menarche at a later age. This has lead to some concern that intensive training might

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