We're going to talk about the aerobic capacity of a young athlete. As the child grows, the components determining the O2 max, there's their lungs and the heart and skeletal muscle, also grow. Consequently, absolute values of maximal aerobic power increases. Here are the VO2 max course for males and females. Once again boys are on blue and girls are in pink. The VO2 max of both boys and girls is at the same level its 6 years of age, and between 6 to 12 years. Both of the boys and girls increased their VO2 mags at a fairly steady rate, reflecting the prepubescent growth of the VO2 mag structures. Then at around 12 years of age notice the rapid increase in the VO2 max of boys is they quickly outstrip the girls. Also note how the VO2 max of the girls plateaus at about 14 years of age. To explain this gender difference in VO2 max we have to remember that VO2 max represents the maximum amount of oxygen the active lean tissue is consuming. As boys grow they develop more active lean tissue than girls do. So some of the difference between the VO2 max of boys and girls Is due to growth of muscle tissue. Testosterone also plays a role in increasing the male lean body mass. Girls, on the other hand, stop developing significant muscle mass at around 14 years of age. And their additional weight is due to fat mass rather than lean body mass. The additional fat mass doesn't contribute to VO2 max. And this explains the plateau and decline as the female gets older. Also remember that a bigger child of either gender will usually have more muscle and therefore are larger the VO2 max regardless of age. Between eight to 16 years, boys can have an average yearly increase and peak VO2 of around 11%. For girls, the growth in VO2 max increases by almost 12% per year between 8 to 13 years. At age 14, the difference between boys and girls is around 25%. And by age 16, the difference can be up to 50%. Now these data are for all children and are not specific to trained children. We are going to address trained children shortly. So if we look at the aerobic capacity from a relative rather than absolute perspective, we see an interesting picture emerging. Remember, now we're looking at VO2 max in terms of the amount of oxygen consumed per kilogram of body weight per minute. VO2 max is relatively stable in males throughout childhood and adolescence as is indicated by the flat VO2 max line. In females, you see a decrease in VO2 max after about age 10, and this is probably due to the increasing ratio of fat mass for females. As females mature, they carry more fat mass, and since the measure of VO2 max does not account for this it probably explains some of the decrease in the aerobic capacity of girls. When the influence of body fat is removed, the difference between boys and girls remains but it is much less pronounced as you can see here. The VO2 max value for boys remains constant until around 16.5 years and continues to decrease by 6% by the age 21.5 years. And girls they decline stats at age 14.5 years and continues to decline an additional 15% by the time they reach age 21. Now, these data suggest that when considering the aerobic capacity of the muscle fiber for both boys and girls, they both lose relative aerobic capacity as they age. And since these data are for untrained children, one explanation for this phenomenon is that both genders become less active as they age. However because boys maintain a higher level of activity than girls through puberty and beyond, they lose less of their aerobic capacity.