NUTRITION IN SPORT

(Martin Jones) #1

et al. 1989), suggesting that the short stature of
the elite gymnast is determined largely by
genetic rather than training and nutritional
factors. Although Theintz et al. (1989) found no
evidence that the predicted adult height for a
group of elite young female gymnasts, who had
already been training intensively for a period of 5
years, was less than the target height, their subse-
quent work suggested otherwise (Theintz et al.
1993). However, for this question to be resolved,
both groups of athletes (Theintz et al. 1993;
Baxter-Jones 1995) need to be reassessed to ascer-
tain their actual adult height.
The biological maturity status of athletes has
also been studied extensively, especially age at
menarche (Malina 1994; Beunen & Malina 1996).
When considering the influence of nutrition
on the biological development of the elite young
athlete, it is important to remember that this
analysis is beset with a number of difficulties.
Firstly, the definition of what constitutes an elite
young athlete is vague, and secondly, as already
discussed, it is likely that young athletes self-
selected themselves for their sport due to their
appropriate size and physique (Baxter-Jones &
Helms 1996). A girl’s menarcheal age is closely
related to her mother ’s menarcheal age and this
appears to be due mainly to a genetic influence
on hormonal changes (Tanner 1989). Potential
environmental influences include physical activ-
ity and nutrition (Malina 1983). In abnormal cir-
cumstances, nutrition may play an important
role in the attainment of menarche, although this
clearly relates to the malnourished child. It has
been hypothesized that young athletes undertak-
ing intensive training have delayed menarche
due to the effects of training at an early age. In the
British longitudinal study (Baxter-Jones & Helms
1996), all the sports (gymnastics, swimming and
tennis) had later mean ages of menarche (14.3,
13.3 and 13.2 years, respectively) than the previ-
ously reported UK reference value of 13.0 years
(Fig. 32.3). A positive correlation was found
between menarcheal age in mothers and daugh-
ters (n=201,r=0.27,P<0.01; Baxter-Jones et al.
1994). Analysis of covariance, using maternal
menarcheal age, socio-economic group, duration


of training and type of sport confirmed that
maternal menarcheal age and type of sport have
a significant influence on the subject’s age of
menarche. As maternal menarcheal age and
sport were the best predictors of menarcheal age
in the athletes studied, it would appear that
menarche was intrinsically late rather than
delayed (Baxter-Jones et al. 1994); this suggests
that some form of sport-specific selection had
occurred.

Nutrition and performance

The remainder of this review will be limited to
nutritional factors that could affect performance
in the young athlete. Performance will be delim-
ited to three major sporting areas: strength and
flexibility-based sports (gymnastics), endurance
sports (running/cycling) and high-intensity
intermittent sports (soccer, rugby, basketball).

Carbohydrate and fat
The major substrates used by the muscles during

the young athlete 433


15

12

14

13

Gymnastics

Age of menarche (years)

Swimming

UK
median
age

Tennis

Fig. 32.3Mean age of menarche and associated
standard errors for British mothers () and daughter
athletes ( ) in different sports, with reference to the
UK median age (Tanner 1989). Significant differences
were found between mothers’ and daughters’ age of
menarche in gymnastics and tennis (P<0.05). From
Baxter-Jones et al. (1994), with permission of Taylor &
Francis.
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