Stretching allows as full a range of motion to the joints as our genetics or physical condition allows. The body's second circulation system, the lymphatic system, is an important part of its defense against disease and toxins. Movement of the lymphatic fluid toward the heart is partially dependent on muscular compression of the lymphatic vessels. Exercise is an excellent stress reducer. Stress manifests itself in the form of muscular tension and hormonal imbalances.
Exercise releases the tension in muscles and stimulates the hormonal system.
Exercise is a much more effective deterrent to stress than drugs or alcohol. Exercise results in a general improvement in bodily function, combined with improved lymphatic low and increased immune hormonal balance. For each benefit I've covered here, there are 10 maybe 100 more. When the independent changes are combines, the synergistic total effect is awesome. During and after an aerobic workout, we feel good because of a combination of the above effects.