Warming up the body before any intense physical activity is important to your health; as well as cooling down. What do I mean by intense? I mean any activity that raises the heart rate beyond its daily comfortable range. It would not be wise to randomly attempt to lift a 300 lbs. barbell, or even a set of 30 lbs. dumbbells, or running a half marathon without warming up and cooling down. (And of course, you wouldn't want to attempt any of these extremes without proper training.) Why?
First up, warming-up does a number of things like expanding your cardiorespiratory system’s capacity so you are able to breathe efficiently and carry a ready supply of oxygen and other nutrients in the blood to the muscles; that your muscles will desperately need during your workout.
You will want to warm-up gradually, the heart and lungs have a heavy demand to supply the muscles with oxygen and nutrients in order to produce force. Without warming up the heart and lungs you are forcing those organs to supply and demand, on point, without being prepared.
It's like going to work and doing a presentation that can change the fate of the company with no prior experience or knowledge of the subject you are supposed to be presenting. It wouldn't do you much good.
Forcing the body to produce force with no ready supply of ATP or oxygen is setting up the muscles to fail before they even begin. This can lead to serious injuries and lead to issues in the cardiorespiratory system.
Warming-up the body is literally what it says! Your body temperature will rise. What’s the purpose? The rise in body temperature increases your muscles range of contraction. In other words you reduce the risk of injury because the muscles have a wider range to lengthen while under contraction.
Rise in the tissue temperature will increase your metabolic rate and prepares your mind for the hard work that you are about to put your body through.
This is important because we want to avoid and prevent injury. For example, if you haven’t worked out in over three months and you decide to lift up 30 lbs. dumbbells without warming up, you will more than likely tear the muscle beyond repair and you will be left with a painful injury, which will take at least six weeks to recover and then you find yourself back at square one.
Do your body a solid and warm it up; think of it as insurance, it’s a pain in the rear and time consuming but you’ll appreciate it when it does its job.