Physical fitness is not limited to a lean or buff appearance. Fitness is determeined by the ability of the muscular, circulatory and respiratory systems to meet increased intensity demands. There are five basic elements that, together, lead to overall fitness. With optimal fitness levels, come numerous health benefits -- improved quality of life, the staying power to perform everyday tasks without undue fatigue, and a reduced risk of illness and injury.Cardiovascular endurance is measured by how efficiently your heart and lungs provide fuel, in the form of blood and oxygen, to your tissues and cells to sustain continuous movement. You can keep track of cardiovascular fitness by tacking your heart rate while performing continuous movement using large muscle groups -- while running on a treadmill, for example. Other assessments measure distances traveled while jogging or the time taken to complete a specified distance. Improved cardiovascular endurance results in a reduced risk of high blood pressure, heart attack, stroke and other heart-related problems.Muscular fitness is based on the ability of your muscles to exert force to overcome resistance. Check muscle strength by measuring the amount of force needed to overcome maximal resistance in an exercise in one effort. An example is the amount of weight that can be lifted in a one-repetition bench press. Build muscle endurance by performing many repetitions of a lower resistance exercise with a less than maximal amount of force. An example is the number of pushups that can be performed using your body weight as resistance. Optimal strength and endurance help to increase muscle mass, improve posture and alignment, and reduce the risk of back problems and joint injuries.Defined as the range of motion of your joints, surrounding muscles and connective tissue, flexibility is joint specific, so no one test can assess overall flexibility. Evaluations, such as the sit and reach, are based on the distance that your body covers while performing stretches. While sitting with your legs extended in front, hinge at the hips to extend your upper body towards your feet. If you can touch your toes, your hamstrings, the large muscles along the back of your thighs, are flexible. Adequate flexibility enhances physical performance while lowering the risk of injuries.Compare lean body mass to body fat to determine body composition. Assessments are based on the percentage of body fat to total body weight. Recommended body fat percentages depending on age, according to Sports Fitness Advisor, range from 14 to 25 percent for women and nine to 19 percent for men. Excess body fat percentages increase the risk of obesity and health-related problems such as diabetes and heart disease. Body composition levels can be managed with a combination of exercise and proper nutrition.