Increase blood flow, oxygen, and nutrition to the connective tissues prior to and after exercise. Repetitive isotonic activity delivers enhanced blood flow which carries the oxygen and nutrition to the muscles. Fuel for muscle action comes from the deployment of fatty acids and glucose accompanied by oxygen. Glucose emanates from glycogen, which is stored muscle fuel derived from carbohydrates in your diet. If oxygen is lacking due to improper warm-up, then oxygen will be deficient, causing the muscles to get energy by converting glucose to lactic acid.
Lactic acid is a waste product or toxin that causes muscle to fatigue and ultimately fail.
Drinking water and stretching after exercise will cause the lactic acid to dissipate, leaving you pain free and flexible for your next endeavor. Stretch to the point of mild discomfort, not pain. However, to increase the range of motion it is necessary to reach the existing limit regularly and exceed it. Intensify the contraction of the agonist muscles opposite to the antagonist muscles that are reciprocally relaxing and lengthening on the opposite side of the joint. Contraction of certain muscles will cause a concomitant relaxing and lengthening affect with the opposing muscle.