The research is fairly clear on a few things. Brain circuits, important for sport performance, for example, develop at different times. And this impacts the appropriate introduction of specific forms of training. The general window for opportunity for most gross motor skills is between birth and around five years of age. Movement experiences during this period lay down the brain circuits dedicated to motor control. These circuits connect the cerebellum that receives information from the sensory systems, from the spinal cord and from other parts of the brain, and then regulates the motor movements such as posture, balance and coordination, resulting in a smooth and balanced muscular activity. Before age five, different movement experiences have a really strong impact on early brain development and motor control. And this I believe is fairly well established. Now the windows of opportunity for fine motor control typically follow the peak in gross motor development, and is open until around nine years of age. Movement experiences during this time period develop the primary circuits needed for learning the type of sports skills requiring high degree of hand and foot and limb dexterity and coordination. The general window of opportunity for attaining reasonable proficiency in most motor abilities narrows around ten years of age. And the ability of the child to easily learn more complex motor skills after ten years of age, we flex the experiences that began prior to age ten. And when we examine the period of accelerated development of motor performance abilities, we see that they're occurring in two different phases. One period occurs before puberty and is related to the chronological age related enhancement in neuromuscular efficiency, due to the maturing nervous system. And we talked about these nervous system maturations in the previous module. The second phase occurs during and after puberty, with our increases in hormone levels and muscle fibers type develops and there are changes in the muscle mass. Movement exposure during the naturally occurring growth and maturation before puberty is analogous to putting the throttle for developing future athletic talent halfway down. Theoretically the addition of a wide variety of movement exposures during these naturally occurring accelerating periods of growth pushes the throttle closer to the floor. And this further accelerates and enhances motor development beyond what might have occurred naturally. Now it's not possible to raise the athlete's genetic ceiling through these movement exposures during these prepubescent acceleration windows. However exposure during these sensitivity windows potentially optimizes, or perhaps even enhances, the structural growth and therefore, noted performance abilities. And this potentially allows the athlete to more easily reach their genetic potential after puberty. Enriched environment exposures could also permit athletes to reach their genetic potential sooner, providing a fully developed athlete with a longer time for maximal sport performance. That is five years instead of three years. And whether this effect occurs or not is not known and requires additional research. Okay, so returning to the leg stiffness research, there are two possible explanations for why we see a period of decline in leg stiffness and other motor performance abilities right before puberty. This is the body may have insufficient energy to concurrently manage both sexual maturation and improvements in motor performance abilities. That is the brain can't multitask. And second, the body needs to direct all its resources to building structures from maturation. And when the maturational structure building phase is completed, resources then are redirected back to improving structures necessary for the motor abilities, so they match the new maturational level of the body. In essence, motor abilities accelerate in order to catch up to the child's enhanced physical growth and sexual maturation. Aggressively enhancing motor abilities inside the appropriate sensitivity window potentially stimulates an even higher growth of the structures that will enhance the specific motor ability.