Physical fitness is an integral part of overall good health, and is attained through regular exercise, eating a balanced diet, and getting the right amount of rest. Fitness can be categorized in the following ways:

• Flexibility
• Cardiovascular endurance
• Muscle strength
• Endurance
• Agility
• Balance
• Speed
• Body composition.

Flexibility refers to one's ability to move with full range of motion (how limber one is). Cardiovascular endurance, sometimes referred to as aerobic fitness, relates to an ability to engage in somewhat strenuous activity for a period of time, reflecting how well the lungs and heart work to oxygenate the body during physical activity. Muscle strength relates to how long a position can be held or how many times a particular motion (i.e., lifting weights) can be repeated. Agility and balance are closely related to flexibility, and are indicators of overall physical fitness. Body composition relates to the ratio of body fat to muscle, or body mass index (BMI).

The Obesity Epidemic

The overall lack of physical fitness in the United States has become a serious problem, with obesity rates having risen by over 60 percent in the last ten years. Obesity is highly correlated with diseases such as type II diabetes, which increased by 49 percent during the 1990s. Type II diabetes used to be unknown in those under the age of 20, but now accounts for 50 percent of the newly-diagnosed cases among the young.

Children and Fitness

Today, nearly 9 million young Americans, or 15 percent of America's youth, are overweight. As being overweight is highly correlated with a lack of physical activity, achieving physical fitness is an important tool in the struggle against childhood obesity. Children need to spend less time watching TV, playing video games, or sitting at the computer. Instead, they should engage in active play, athletics, running, bike riding, jumping rope, or dancing.

Aerobic Exercise

For adults, there are also many ways to increase physical fitness, with an emphasis on aerobic and strength training. The American College of Sports Medicine defines aerobic exercise as "any activity that uses large muscle groups, can be maintained continuously, and is rhythmic in nature" -- in other words, anything that gets the heart and lungs working more than usual. Such exercises might include: aerobic dancing, cycling, cross country skiing, in-line skating, fitness walking, jumping rope, running, stair climbing, and swimming.

Strength Training

Strength training may include a variety of weight lifting activities such as bench press, bicep curls, squats, leg extensions, and abdominal crunches. It is generally recommended that aerobic exercises be done three to five days per week, from twenty to sixty minutes of continuous activity at a time, such that the heart rate increases from 50 to 90 percent, depending on the intensity of the workout. Strength training should be accompanied by a warm up and cool down period, and be attempted only if the body is ready for it. As with aerobic exercise, it is recommended that one who is not used to exercise consult with a physician first to see what level of exercise is safe and beneficial.