There are many ways to identify physical fitness. It may be helpful for you to think about physical fitness in relation to “specificity of training” which means that physiological adaptations to exercise are specific to the system worked during the stress of exercise. In other words, the type of exercise that develops cardiovascular endurance is not very effective for developing an optimum balance of muscular strength. Flexibility training usually increases the range of motion about a specific joint, such as the hip, but it is not effective for improving cardiovascular endurance or muscle strength. Resistance training, such as weightlifting, is the best way to increase strength, but it is not the most effective way to improve cardiovascular fitness.
Optimum physical fitness is often defined as the condition resulting from a lifestyle that leads to the development of an optimal level of cardiovascular endurance, muscular strength, and flexibility, as well as the achievement and maintenance of ideal body weight. Because training is specific, as described above, an individual must participate in cardiovascular, strength and flexibility exercise to achieve optimum (balanced) physical fitness.
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Cardiovascular, or cardiorespiratory endurance, also referred to as aerobic fitness, describes the ability of the cardiovascular / cardiorespiratory system (heart, lungs, blood vessels) to deliver an adequate supply of oxygen to exercising muscles. Blood must flow from the heart through blood vessels to the lungs to pick up oxygen that can be delivered to exercising muscles.
Muscular strength is the maximum amount of force a muscle or muscle group can develop during a single contraction. Muscular endurance is the number of repeated contractions a muscle or muscle group can perform against a resistance without fatiguing, or the length of time a contraction can be held without fatigue.
Flexibility describes the amount of movement that can be accomplished at a joint, such as knee or shoulder, and is usually referred to as the “range of motion about a joint”. Maintaining flexibility may help reduce the risk of injury and can also help improve performance in many activities.