Another interesting curve is represented by the subcutaneous fat layer in the body which is rather complicated in comparison to the other tissues and was described by Tanner in 1962. The width of the subcutaneous fat is measured either by X-rays or by specially designed skinfold callipers applied to a fold of fat pinched up from the underlying muscle. The distance and velocity curves of skinfolds taken over the triceps muscle (triceps skinfold thickness) and under the angle of scapula (subscapular skinfold thickness) are summarised in figure 3.4 and figure 3.5, respectively. The subcutaneous fat usually begins to be laid down in the foetus at about 34 weeks and subsequently increases from then until birth, and from birth .mtil 9 months in average child; while in some the peak may be reached as early as 6 months and in some it may occur as late as 15 months. From 9 months, when the velocity is thus zero, the subcutaneous fat decreases, Le., has a negative velocity, until age 6-8 years when it begins to increase once again.
It should be well kept in mind that the decrease in width of fat layer must not be confused with the decrease in the cross-sectional fat area. The fat is a ring around a musculo-skeletal centre which is increasing at all ages; if the cross-sectional fat area stayed constant the width of the ring would be reduced simply by enlargement of the musculo-skeletal core. However, calculations from measurements of fat on X-rays show that cross-sectional area does in fact decrease during the early childhood years. The decrease is less in girls than boys, so that after the age of one year girls possess more fat than boys. The increase from age 7 years is however, noticed in both sexes, in both limb-fat and body-fat. But at adolescence, the limb-fat in boys decreases and not gained until the age of20 years. In boys’ trunk-fat a much smaller loss (if at all) occurs; there is only a temporary halt to the gradual increase. On the contrary, in girls there is a slight halting of limb-fat increase, but no loss; and trunk-fat shows nothing but steady rise. The decrease in extremity skinfolds during the adolescent spurt in males contributes to the sex differences in subcutaneous fat distribution. Girls at all ages have more subcutaneous fat than boys and show proportionate development of limb and trunk fat during adolescence. The decrease in the fat distribution at several regions of the body in both sexes during adolescence is mainly attributed to the utilization of energy reserves offat for peak growth spurt.
Sample Questions
- 1) What do you understand by growth curves? Elaborate how a distance curve is different from a velocity curve.
- 2) Describe Scarnmon’s curves of different tissues and organs of the body.
- 3) What is a sigmoid curve? How is it different from that of a neural curve?
- 4) Describe the growth curves of subcutaneous tissue. Flow these curves vary among boys and girls with reference to limb fat?