What is a one-sentence summary of the following article?
It is commonly advised that stretching before exercising can actually hurt you. That is the case with static stretching, or holding the muscles still in a stretched out position. Dynamic stretching, on the other hand, involves deliberate motions which gently stretch your muscles in preparation for more rigorous exercise. Performing these exercises can greatly reduce the risk of hurting yourself or developing a cramp. It is important to warm up every muscle group in your body prior to exercising. Some dynamic exercises you can do for the upper body include:  Arm circles. Extend your arms out to either side and gently rotate them in a tight, circular motion. Shoulder rolls. Stand up straight and slowly rotate your shoulders backward. Try to touch your shoulders to your ears as you do this. After a few repetitions, switch directions and move your shoulders forward. For a cardiovascular workout that involves running, jogging or hiking, it is crucial to warm up your legs. For weight training, your legs need to be prepared to do most of the heavy lifting. Here are some examples of dynamic leg exercises:  Lunges. With your hands on your hips, take one large step forward. As your foot touches the ground, drop your back knee straight down as far as you can without touching the ground. Pushing off your back foot, swing your back leg to the front, repeating the dropping motion with the other leg. Knee lifts. Instead of dropping your knee downward, lift your opposite knee up to your chest as you take a step forward. This should look like a very exaggerated march. Back muscles are extremely prone to cramping during all types of exercise if they have not been properly warmed up. There are tons of different back exercises, including:  Torso twists. Stand with your feet shoulder-width apart and your arms bent at a 90-degree angle. Gently twist your torso back and forth. This motion mobilizes your spine. Standing back bends. With your hands on your hips and feet shoulder-width apart, lean back slightly, pressing your hip bones forward. Return your upper body to the upright position, and repeat several times.

Summary:
Prior to exercising, perform dynamic stretches. Begin by warming up your upper body. Move on to your lower body. Finally, you need to warm up your back muscles.