To fully understand the evolving nature of the child's physical work capacity and exploitation capabilities, and to therefore the quality of their sports performance, we must venture into the field of ontogeny. Now ontogeny is a branch of biology that examines how an organism slowly evolves from an embryo all the way through to an adult. And then the case of the young athletes, the magnitude and multitude of the dramatic changes in shape and physiology of their body as they evolved into an adult is noticeable in the quality of the sports performance. Understanding the maturation of the child from the perspective of ontogeny, potentially provides a better indicator for identifying future early talent than the more common champion model that's currently used, and the champion model it assumes that children are simply miniature adults. And assesses this port talent by looking at how closely they resemble of physique and motor performance abilities of an elite athlete. Indeed, it is really really tempting to take this view, because we know from simple observation that children do get bigger with age. External changes reflect internal changes. A 16 year old boy for example, has lungs and oxygen capacity almost three times larger than it was when he was five. His heart is 2.7 times bigger that it was 95 grams at 5 and it is 258 grams at 16. A girl has tripled the grip strength at 16 than she had when she was age 5. Her muscle mass increases from 7 kilograms to 23 kilograms. And the longer leg length allows a 16 year old to run faster and with fewer strides, resulting in a lower oxygen requirement than a five year old must have. In other words, there is no question a child is smaller than an adult. And we also know that the child will eventually become an adult, and it doesn't take much brain power to figure this out, but this miniature adult view ignores how the body evolves into the adult form. It doesn't tell us what happens if the environmental conditions in which the child is growing is not conducive for allowing maximization of a genetic potential. Ontogeny provides these insights by explaining how the structures increase in size and their rate of growth by taking the environmental conditions into accounts. The body structures and physiology of a child do not evolve into an adult form at a uniform rate nor do all the potential elite athletes have the correct environmental conditions as a child to ensure successful evolution into an elite athlete. So let's just take another look at this chart, and we can see that there are periods of unstable transitions consisting of both progressions and regressions, lodged between short periods of stability. And this explains why a child's performance will accelerate at times, and in other times it will stabilize. And in other times, it will regress. And if you happen to be coaching a child who is in the regression phase, both you and the child will equally frustrated if you don't understand why this regression might be occurring. Now research on the leg stiffness of children nicely illustrates this phenomenon. When landing while running or jumping the touch down knee will bend slightly as it catches the body weight. The amount of bend provides an indication of leg stiffness. The less the bend,the stiffer the leg. And the yellow circle here indicates the knee bend phase of this runner as his body weight is moving over the knee so the leg can push off for the next stride. The leg stiffness study used boys between ages 7 to 16 years of subject to explore how the stretch shortening cycle responded as they aged. In the stress shortening cycle is an active stretch of the muscle followed by an immediate shortening. And the runner's thigh muscles here will stretch as they catch the weight of the body, and then, they will contract to accelerate the body forward. The same thing happens to the calf muscle and the Achilles tendon. The stretch shortening mechanism is fundamental to running and jumping and is a factor in leg stiffness. In the study, the young athlete's reactive strength was assessed using a hopping test involving five maximal vertical hops on a contact mat that was able to measure the contact time and the flight time. And the boys were instructed to maximize jump height and minimize ground contact time. And then an equation was used to assess leg reactive strength, and this equation was reactive strength, is equal to the jump height and that was in millimeters divided by the ground contact time, and that was in milliseconds. So, let's go back and take a look at the graph of the data. The black dotted line is the speed of growth of the child that we discussed in the previous module. And the red dotted line represents the leg reactive strength index. And the index actually indicates how quickly the stretch sensors and the muscle and the tendon react to maintain leg stiffness. Now stiffness of the leg is reflected in the knee bend upon landing. And a small knee bend is desirable because a stiff leg allows for faster speed and higher jumps. Now notice how reactive strength increases linearly between age 9 until about age 10. And then there is an accelerated increase between age 10 and 11. And then between age 11 and 12, there is a decline in leg stiffness. And this decline occurs immediately before the growth spurt. Now in this area corresponding to the growth spurt, there is an increase in leg stiffness. And this increase in leg stiffness continues until age 16 years. And it so happens that endurance, speed, and strength all show a similar fluctuation between accelerated improvement, followed by decline, and then followed by an accelerated improvement again. And the question is what on earth is going on here? And we're going to come back and answer those questions shortly after we examine another concept related to critical and sensitive periods of a child's development. And this concept is the notion of windows of opportunity.
