Problem: Children tend to have hypokinetic circulation (Bar-Or, Shephard, & Allen, 1971); that is, their cardiac output is less than an adult's (cardiac output is the product of stroke volume and heart rate). Children have a smaller stroke volume than adults, reflecting their smaller hearts. They compensate in part with higher heart rates than adults at a given level of exercise, but their cardiac output is still somewhat lower than an adult's. Need Professional Help?