The main reason for warming-up is to prepare your body for more physical demanding activity that is to follow. A progressive warm-up begins an adaptation process in both your cardiovascular and musculoskeletal systems, which reduces the risk of premature physical overload and traumatic injuries. For example, as you warm-up your heart rate and systolic blood pressure gradually increase to accommodate the demands of higher activity levels. In addition, your blood vessels open up and previously closed capillary levels are activated to enhance blood flow to the working muscles. As your body temperature increases, muscles, connective tissues and joint structures warm-up for more efficient function.

Of course, the mental aspects associated with warming up should not be discounted. A standard pre-exercise warm-up procedure puts you into the proper mindset for a productive workout. Without an appropriate warm-up routine, you may find it difficult to begin your training sessions at the right intensity for a safe and sustained workout. That is, you may start too fast or too slow and never seem to hit your desired stride.

The reasons for including a cool-down segment in your exercise session are even more compelling. Certainly, cooling down provides a smooth transition period between your activity state and your resting state, in much the same way as the warm-up. Even more important, however, is the cool-down's effect on blood circulation and heart recovery. Consider that during a 30-minute jogging or cycling sessions your heart is circulating large quantities of blood throughout your body, and especially to the large muscles of the legs that are doing most of the work. If you simply stop exercising, the heart keeps pumping blood to the legs, but the muscles are no longer moving in rhythmic patterns that facilitated blood return back to the heart. As a result, blood tends to accumulate in the legs and an insufficient blood return causes the heart to work harder in an attempt to force more blood through the system.

A secondary outcome of blood pooling is a feeling of lightheadedness or even fainting due to inadequate blood-oxygen supply to the brain. Fortunately, by continuing to move after you cross the finish line you can maintain normal circulation and avoid these potentially harmful consequences. Even slow walking provides the piston-like pumping action n your leg muscles that squeezes blood through the one-way valves in your veins back to the heart.

So instead of suddenly stopping your exercise, slow down gradually and keep moving for at least five minutes after your training period. Of course, a harder workout requires a longer cool-down, that is, it takes more time to transition back to rest from a fast 30-minute run than from a slow 30-minute walk.

As you near the end of your cool-down, you may conclude with a few gentle and relaxing stretching exercises. It is generally recommended to perform your stretches when your body is fully warmed up and most flexible. This makes the cool-down the perfect place for your stretching routines. It also assists in leaving your workout feeling invigorated rather than exhausted.

Suggested Warm-Up and Cool-Down Routines
There is no specific formula for determining the optimum warm-up and cool-down protocols. Basically, this depends on a variety of factors, including your age, physical ability, the type of exercise activity and the level of training intensity.

Generally speaking, your warm-up and cool-down programs should be longer if you are older, less physically fit, or if you are exercising at a more challenging training level. For example, an older beginning exerciser may divide a 20-minute workout into about seven minutes of warm-up activity, seven minutes of actual training, and seven minutes of cool-down activity. As another comparison, a 30-minute walking workout may be safely sandwiched between a five-minute warm-up and a five-minute cool-down, whereas a 30-minute fast-paced stairclimbing session may require a seven minute warm-up and a 10-minute cool-down for beet results.

My suggestion for an effective warm-up is to begin with some abdominal exercises such as trunk curls, and twisting trunk curls for the important midsection (core) muscles. These may be followed by some half-squats or chair squats that address the large quadriceps, hamstrings and gluteal muscles of the hips and thighs. Next, perform a few standing exercises such as trunk bends and turns, shoulder rotations and gentle neck stretches. Then do at least a couple minutes of the workout exercise (walking, cycling, stairclimbing, etc.) at a very slow pace, gradually progressing towards your desired training intensity.

After completing your workout, please, move immediately into your cool-down phase. Your first step is to continue the training exercise for a few more minutes, while continuously slowing the pace to an almost effortless exertion level. When your heart rate has returned within 20 beats of resting (typically 80 to 90 beats per minute), you may perform a few walking stretches followed by a few standing stretches. Finish with some seated stretches, such as the Figure A stretch, and some supine stretches, such as the Letter T stretch.

Although warming up and cooling down add a little time to each training session, you will find that it is time well spent and time that enhances both your workout performance and your recovery ability. Warming-up and cooling-down may also make the difference between intermittent physical problems and injury-free exercise experiences.

Wayne L. Westcott, Ph.D., is fitness research director at the South Shore YMCA in Quincy, MA., and author of several books including the new releases Strength Training Past 50 and Strength and Power for Young Athletes.