Injury or Fainting. Warm-up and Cool-Down. You Decide.

Warm-up
You must prepare your body before taking part in physical training, sports competition, or vigorous physical activity. A warm-up may help prevent injuries and maximize performance.
The warm-up increases the body’s internal temperature and the heart rate so that more oxygen-rich blood can be pumped through the muscles. The chance of getting injured decreases when the heart, muscles, ligaments, and tendons are properly prepared for exertion and, vica versa the risk of injury increases unnecessarily when you do not go through a proper warm-up.
A warm-up should include some running-in-place or slow jogging, stretching, and calisthenics. Get all the major muscle groups involved in the warm-up and pay particular attention to warming-up the parts of the body that will become subject to the most stress during the conditioning activity. After stretching all his major muscle groups, a major-league pitcher warms-up by throwing baseballs at increasing velocity. The last couple pitches are at game speed. Warming-up from the general to the specific like the major league pitcher is a good model to adapt and follow.
A good warm-up should last five to seven minutes and should occur just before the sports activity or muscular endurance and strength part of the workout. The warm-up effect won’t last more than five minutes or so. If the delay before the intense physical activity begins exceeds five minutes then perform at least one or more mini-warm-ups before starting. After a proper warm-up, you have prepared your body for a more intense conditioning activity.
Cool-down
You should cool down properly after each exercise period, regardless of the type of workout. Even swimming needs a cool down. The cool down serves to gradually slow the heart rate and helps prevent pooling of the blood in the legs and feet.
During exercise, the muscles squeeze the blood through the veins. This helps return the blood to the heart. After exercise, however, the muscles relax and no longer do this, and the blood can accumulate in the legs and feet. This can cause a person to faint. A good cool-down will help avoid this possibility.
During the warm-up you specifically engaged the muscle groups that you would be using during the conditioning activity. You do not have to engage the same muscle groups again for the cool down. For a proper cool down you can walk and stretch until your heart rate returns to less than 100 beats per minute (BPM) and heavy sweating stops. This usually happens five to seven minutes after the end of the conditioning activity.
You can check your BPM on the radial artery on your wrist (just above the base of the thumb), a carotid artery on your neck (just beside the Adam’s apple), or by putting your hand over your heart. Count the beats for 10 seconds and multiple by 6 to get BPM.