The most common or popular method of warming up is stretching. However, it is well known that in order to have an effective stretch, the muscles must already be warmed up especially in the case of static stretching, which is typically recommended. But, if you already warm-up prior to doing stretches, why is it necessary to do stretching?
Many experts recommend stretching before a strength or cardio workout. Rarely asked is how much stretching is needed and what is the purpose of the stretching. Keep in mind that stretching is used to either 1) increase the range of motion in the joint, or 2) regain the normal range of motion in the joint after being sedentary for a certain period of time.
In the latter case, stretching is important before working out so that you are capable of going through the full range of motion in the exercise. In this case, rather than doing static stretching, which is used mainly to increase flexibility, you should do active stretching which not only regains the normal range of motion, but also warms up the muscles at the same time. In this way you accomplish two goals at the same time.
In active stretching, the muscles are involved in the stretch. When the muscles contract on one side of the joint to move the limb or body through a particular range of motion, the muscles on the opposite side of the joint undergo an eccentric stretch. In the process the muscles develop tension while they relax and thus develop heat to get warmed up. Active stretches can also be done with weights, once you are warmed up. By going through the full range of motion, with ample resistance, you can gain strength and flexibility at the same time.