All exercise involves meaningful muscular work. In order to be effective, exercise must be hard. If it is hard, it must be safe. Otherwise, unwanted side effects of pain and injury are the likely result. Slow-motion, high intensity strength training offers the ideal exercise prescription because it maximizes muscle effort while minimizing joint impact. Working out at optimal intensity requires less time due to rapid fatigue and lower frequency because muscles strengthen as you recover from the challenge. Most importantly, stronger muscles enable better performance of all the other activities you need and want to do.