Muscles get tight after a heavy weightlifting sessions. Some trainers state that it is wise for body builders to stretch or do yoga at least three days a week. On your rest day (s) you should consider engaging in yoga, light walking, or other forms of activity that keep your blood flowing but still allows for significant rest. You don't want to be one of those guys/gals that get so tight they lose their range of motion and begin to rip muscles. Think of total health.