An active student injured his knee playing basketball and has been advised by his doctor to avoid impact activities that cause heavy force on his bones. what is the most effective activity he can do to maintain his stamina without further injury?

If it's a smaller child or infant, place one on the middle of the chest and on the child's back. (if it is a bigger child with enough room for two, place one on the upper right/your left of the chest, and one on the lower left/your right) the pads should never touch each other. 

Few days to several months depending on the severity of the stroke ;