Your body will produce more stress hormone, called cortisol, if you exceed an hour long workout. Cortisol blocks testosterone--a hormone that promotes muscle growth--and undermines all of the work you are putting into building muscle. If you keep your workouts under sixty minutes, you will reap the rewards of your efforts faster and enjoy the benefits of your hard work.Bemass Muscle After exercising it is vital to stretch, so that your muscles can build and repair themselves well. Anyone that is under forty years old needs to make sure that each stretch is held for a minimum of thirty seconds. However, if you are over 40, hold the stretch for a little longer, 60 seconds at least.