#345--The nervous system takes longer to recover than the muscular system. Thus, the more neurologically complex the exercise, the longer a person should rest between sets. For example, if you're performing a standard push up, one minute should be an adequate amount of time for the muscles involved in the movement to recover. But if you have your hands placed on a BOSU and one foot on a Physio ball while the other is unsupported, it could require 5-6 times as long before your nervous system has recovered enough to allow you to do the exercise again. Heavier loads are also more neurologically demanding as the body is asked to recruit muscle fibers which are rarely if ever used. So the rest interval between sets of something like heavy squats should be longer than when squatting at a lower weight. Failure to rest sufficiently could result in injury.