1 Growth and Sexual Maturation in Normal Puberty W. A. MARSHALL
At adolescence the maturation of the gonads is accompanied by acceleration of somatic growth (the adolescent spurt), the development of the secondary sex characters and other physiological events. In different individuals these changes vary greatly in the age at which they begin, in the time which elapses from their onset to their completion, and in the sequence in which they occur. These variations are the main theme of the present chapter. THE ADOLESCENT GROWTH SPURT Figure I illustrates the growth in stature, from birth to maturity, of a typical boy and girl. The curve for each child rises steeply in early life and then gradually levels ofT. Later, it suddenly becomes steeper again. This reflects the acceleration of growth which we term the adolescent spurt. This spurt is described more precisely by the lower curves which illustrate the children's rates of growth, or growth velocities, at each age. [t is usual to express growth velocities in 'centimetres per year'. This however does not imply that a given speed is necessarily maintained for a whole year. Just as a motor car may travel at 50 m.p.h. for a few minutes and then change its speed, a child may grow at a rate of, for example, 5 em per year for a few months and then grow at a different speed in the following months. Growth velocity is calculated by subtracting the child's stature at one age from his stature at a later age and dividing this increment by the time which elapsed between the two measurements. The arithmetic involved is quite simple if dates are expressed as decimals of a year rather than in days and months (see Appendix, page 24). The curve of growth velocity plotted against age shows the adolescent spurt as a sharp increase to a maximum, after which the velocity immediately begins to fall again. The maximum value, usually referred to as peak height velocity or PHV, is clearly defined on any velocity curve drawn from repeated measurements of the same child. It is therefore a very useful landmark in the growth process. In the Harpenden growth study 41 girls were measured every three months by the same skilled observer. A velocity curve was drawn for Clinics in Endocrinology and Metaholism-Vol. 4, No. I, March 1975.
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W. A. MARSHALL
each subject. Their peak height velocities, obtained from the curves, averaged 9.0 em/year with a standard deviation (s.d.) of 1.03 em/year. The velocity over the whole year centred on the peak, that is including six months before it and six months after it, average 8.4 em/year. The mean growth rate immediately before the spurt began was in the region of 5.0 em/year for both sexes. During the year in which PRY occurs, a girl may gain between 6 and II em and for some of them the rate of growth during adolescence will be nearly double their pre-adolescent rates. In 49 boys, PRY averaged 10.3 em/year with a standard deviation of 1.54 em/year and the velocity over the whole year centred on the peak averaged 9.5 em/year. 170
Q.)
130
\-.~
.aE
~~ CIJ
90
50 18
I
I \ \
O+---,------,--------y-
o
6
12
18
age (yrs) Figure 1. Above: growth in stature ofa typical boy (solid line) and a typical girl (interrupted line). Below: growth velocities at different ages of a typical boy (solid line) and a typical girl (interrupted line).
The mean age of reaching peak height velocity in the girls studied by Marshall and Tanner (1969) was 12.14 ± 0.14 years with a standard deviation of 0.88 years. Thus adolescent girls may reach their maximum growth rates any time between their 10th and 14th birthdays with a few outside even these limits. For boys the mean age was 14.06 ± 0.14 years with an s.d. of 0.92
GROWTH ANI) SEXUAL MATURATION IN NORMAL PUBERTY
5
years (Marshall and Tanner, 1970), i.e. most adolescent boys reach PHV between their 12th and 16th birthdays. Since the adolescent spurt occurs, on average, some two years earlier in girls than in boys, the majority of boys are still growing slowly while many girls are experiencing their growth spurts. As a result, a girl who experiences her spurt at the average age or earlier will temporarily become taller than many boys of her own age (Figure 1). However, this situation is usually temporary as her growth will slow down as that of the boys is accelerating, with the result that the boys, in general, become taller in the end.
190
170
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E o
At adolescence the maturation of the gonads is accompanied by acceleration of somatic growth (the adolescent spurt), the development of the secondary sex characters and other physiological events. In different individuals these changes vary greatly in the age at which they begin, in the time which elapses from their onset to their completion, and in the sequence in which they occur. These variations are the main theme of the present chapter. THE ADOLESCENT GROWTH SPURT Figure I illustrates the growth in stature, from birth to maturity, of a typical boy and girl. The curve for each child rises steeply in early life and then gradually levels ofT. Later, it suddenly becomes steeper again. This reflects the acceleration of growth which we term the adolescent spurt. This spurt is described more precisely by the lower curves which illustrate the children's rates of growth, or growth velocities, at each age. [t is usual to express growth velocities in 'centimetres per year'. This however does not imply that a given speed is necessarily maintained for a whole year. Just as a motor car may travel at 50 m.p.h. for a few minutes and then change its speed, a child may grow at a rate of, for example, 5 em per year for a few months and then grow at a different speed in the following months. Growth velocity is calculated by subtracting the child's stature at one age from his stature at a later age and dividing this increment by the time which elapsed between the two measurements. The arithmetic involved is quite simple if dates are expressed as decimals of a year rather than in days and months (see Appendix, page 24). The curve of growth velocity plotted against age shows the adolescent spurt as a sharp increase to a maximum, after which the velocity immediately begins to fall again. The maximum value, usually referred to as peak height velocity or PHV, is clearly defined on any velocity curve drawn from repeated measurements of the same child. It is therefore a very useful landmark in the growth process. In the Harpenden growth study 41 girls were measured every three months by the same skilled observer. A velocity curve was drawn for Clinics in Endocrinology and Metaholism-Vol. 4, No. I, March 1975.
3
4
W. A. MARSHALL
each subject. Their peak height velocities, obtained from the curves, averaged 9.0 em/year with a standard deviation (s.d.) of 1.03 em/year. The velocity over the whole year centred on the peak, that is including six months before it and six months after it, average 8.4 em/year. The mean growth rate immediately before the spurt began was in the region of 5.0 em/year for both sexes. During the year in which PRY occurs, a girl may gain between 6 and II em and for some of them the rate of growth during adolescence will be nearly double their pre-adolescent rates. In 49 boys, PRY averaged 10.3 em/year with a standard deviation of 1.54 em/year and the velocity over the whole year centred on the peak averaged 9.5 em/year. 170
Q.)
130
\-.~
.aE
~~ CIJ
90
50 18
I
I \ \
O+---,------,--------y-
o
6
12
18
age (yrs) Figure 1. Above: growth in stature ofa typical boy (solid line) and a typical girl (interrupted line). Below: growth velocities at different ages of a typical boy (solid line) and a typical girl (interrupted line).
The mean age of reaching peak height velocity in the girls studied by Marshall and Tanner (1969) was 12.14 ± 0.14 years with a standard deviation of 0.88 years. Thus adolescent girls may reach their maximum growth rates any time between their 10th and 14th birthdays with a few outside even these limits. For boys the mean age was 14.06 ± 0.14 years with an s.d. of 0.92
GROWTH ANI) SEXUAL MATURATION IN NORMAL PUBERTY
5
years (Marshall and Tanner, 1970), i.e. most adolescent boys reach PHV between their 12th and 16th birthdays. Since the adolescent spurt occurs, on average, some two years earlier in girls than in boys, the majority of boys are still growing slowly while many girls are experiencing their growth spurts. As a result, a girl who experiences her spurt at the average age or earlier will temporarily become taller than many boys of her own age (Figure 1). However, this situation is usually temporary as her growth will slow down as that of the boys is accelerating, with the result that the boys, in general, become taller in the end.
190
170
r(ji'
E o
