Okay, so now let's turn to thermoregulation. Compared with the mature adult, younger children generate more heat per kilogram of body mass when they're exercising. And for this reason, the child's thermoregulatory apparatus is under greater stress during exercise. Taking into account their smaller size, children have a higher density of active sweat glands. But each gland produces two and a half times less sweat than it does for the older athlete. Sweating also begins in a higher core temperature in children. And given these differences, here are some key points to consider when you're training children. First, children cannot sustain activity for as long as the immature athlete. Whenever the environmental temperature exceeds 40 degrees centigrade. Children also have a lower tolerance for swimming in cold water. Second, children are slow to acclimatize to both hot or cold climates. Third, dehydrated children are at risk of heat stroke and other heat related illnesses during hot weather. And when training children in hot weather encourage water replacement every 15 to 20 minutes. And point number four, children wearing protective Swatch clothing are special risk of heat related illnesses. So pay special attention to this when you're training children. Now let's move to the cardiovascular responses. Differences between the mature athlete and children are largely due to a child's smaller body size. The important variables to include are heart rate, which is the number of beats per minute. The stroke volume which is the amount of blood pumped from the heart each beat. Cardiac output is the amount of blood pumped out of the heart per minute and the blood pressure is the other variable to consider. Heart rate times stroke volume equals cardiac output. And this is a fairly common equation that you'll see in sports science. A heart and total blood volume of a child is smaller than that of a mature athlete and this results in a lower stroke volume at all levels of exercise. But to compensate for this, the child's heart beat is much faster, 30 to 40 times faster in fact that any given level of exercise with compare to the mature athlete. Next among heart rate in children under 10 years of age can exceed to 210 beats per minute. In the average 20 year old has a maximum heart rate of approximately 195 beats per minute. Maximum heart rate declines with age and there's independent agenda or level of training. The maximal cardiac output, which remember, is the amount of blood pumped out of the heart per minute of healthy children reaches three to four times it's resting value during exercise. A mature athlete, on the other hand, can reach seven times their resting value. Most of the increases in cardiac output is due to the heart rate in all athletes, in depend on age. In very young children blood pressure is lower than the mature athlete at all levels of exercise. And because of this, the cardiac output is lower. And this is not considered neither beneficial or detrimental to the child.