Aristotle helped define the standards of fitness 2,500 years ago when he taught that a thing that suits its purpose well is fit. Fortunately for us, the cardiovascular system, lungs, skeleton, muscles, endocrine system and all the other amazing components of the body function for our purpose: to live well.

Exercising aids fitness in numerous ways, each involving one or more of those systems.

Increased physical activity causes the heart to work harder than at rest. That increases blood flow, floods tissues with fresh oxygen and removes cellular waste products.

Exercise causes the lungs to draw in extra oxygen to bathe the tissues and help power the heart. Exhalation removes carbon dioxide, a waste product of certain biochemical reactions.

Regular, moderate exercise helps raise HDL (High-Density Lipoprotein) cholesterol (the 'good' type). It helps regulate blood sugar levels and converts stored fat into sugars that are used to provide energy. That process also prevents obesity.

The other benefits of a regular fitness program are more obvious and usually among the more direct goals of most people who make the effort: increased muscle mass, toned legs, buttocks, arms, stomach and healthier looking skin. Along the way, the individual receives the added value of greater strength, improved balance, higher endurance and (often) a better frame of mind.

Different types of routines will emphasize one area more than another. Aerobic routines help the cardiovascular and pulmonary systems, weight lifting focuses on building muscle tone and mass, yoga and pilates helps balance, flexibility and muscular control. But each of these, and several more, help more than just the intended focus group. The body is an integrated system and improving one area almost always has beneficial consequences for others.

All those benefits, at least to a moderate degree, can be had for minimal daily effort. Moderate intensity activity for 30 minutes per day, at least five days per week, will go a long way toward optimizing fitness.

A brisk walk, taking the stairs up one or two flights, a short daily jog, jumping rope and many other simple activities can be carried out with no special equipment or training.

More intense activity, done properly, can raise that level even further. A vigorous tennis game, a few laps in the swimming pool, an hour on the treadmill or exercise bike, or any of a dozen others, can raise your fitness to a peak with only a moderate investment of time and money.

For the truly committed there are, of course, a thousand and one classes at the gym, and every conceivable kind of home fitness equipment to fit a variety of budgets. A daily routine using free weights, followed by a good jog around the park will keep all systems functioning well.

And, as Aristotle taught all those centuries ago, to function well is to live well.

Static and dynamic stretching are two elements in a warm-up routine that help prevent injury and maximize performance. But, consider, why do we warm-up at all? And, are there other aspects to a good warm-up routine?

By performing warm-up routines, you actually do literally just that - warm up the body. Internal body temperature can't raise by a large amount, or you would have all the symptoms of a fever. Nevertheless, the temperature in the muscles can, and should, be raised slightly in order to dilate blood vessels and loosen muscles.

That dilation leads to greater blood flow, which helps oxygenate muscles and remove the waste products of cellular activity. Warm muscles are looser, more supple and flexible. That reduces stiffness and lowers resistance to larger movements. That helps reduce the risk of injury and prepares the body for high-performance activity.

A good warm-up also raises the heart rate, respiratory capacity and the overall metabolic level. Among other benefits, this helps deliver nutrients to muscles that will be useful for the workout to come. Warm-ups help lubricate joints, too, as well as lowering the risk to stretched tendons and tears.

No matter what kind of sport or workout you favor, having a well-functioning cardiovascular system and supple joints and muscles are essential for peak performance and low risk of injury.

A 10-15 minute warm-up period, including static and dynamic stretching activities, should be a low-intensity version of the routines that will be undertaken when the warm-up is complete.

Focus the non-stretching aspect of your warm-up more on the specific types of movement called for by the sport or activity you plan to engage in. If you plan to jog five miles, take a brisk walk, followed by a few gentle laps of a hundred yards or less. If you plan to play tennis or golf, spend a few minutes on low-speed, low-impact swings.

As you progress through the warm-up, gradually increase the speed and range of movement. This helps prepare the body and mind both.

Making the increase gradual helps increase the cardio and lung systems, and slowly cranks up needed body chemicals systems without depleting them. It helps gear up the mind for a high performance routine or sports event, in a way that static or even dynamic stretches won't.

Like any physical activity, don't overdo it. Don't warm-up too much or too fast. The idea is to prepare the body for a workout, not perform one.

At the end, you'll be ready to perform the sport or workout of your choice at peak level with minimal risk of injury.