Components of Physical Fitness
Rather than a single item, physical fitness comprises several components that combine to make performing physical activities easier. These components are divided into the following 2 categories: skill and health related. The skill-related components include qualities that are important in sports performance, such as agility or reaction time. The health-related components are needed by athletes and the general population to reduce the risk of injury and chronic disease. The 5 components of health-related physical fitness are cardiorespiratory endurance, muscular strength, muscular endurance, flexibility, and body composition. Each is measurable and can be improved with exercise training.
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Cardiorespiratory endurance is the ability of the heart, lungs, and metabolic pathways to provide oxygen to active muscles and resist fatigue so that physical activity can continue over a period of time.13 Aerobic exercise improves cardiorespiratory endurance by increasing one’s heart rate (HR) and oxygen consumption for extended amounts of time. Physical activity research has long focused on cardiorespiratory endurance and continuous aerobic exercise as being the key to reducing the risk of chronic disease. More recent studies14 suggest that shorter bursts of strenuous activities, such as sprinting, can also improve the risk factors for CVD.
Muscular strength is the ability to create enough force to move a heavy object once. Muscular endurance is the ability to perform multiple contractions one after another. Exercises that improve muscle strength and endurance are important for maintaining health and physical function. The pull of the muscles on bone, particularly those at the pelvis and spine, encourages the regeneration of bony tissue that prevents osteoporosis.15 Muscles respond to exercise by increasing the number and size of their fibers. This adaptation helps reduce the loss of muscle tissue in older adults. The loss of muscle with age has negative effects on force production and balance; the risk of falling is greater in older adults who do not exercise.16
Flexibility is the ability to move one’s joints through normal ranges of motion (ROMs) without pain or limitation.17 An individual’s flexibility is based on several factors, such as age,18 gender,19 types and volume of physical activity,20 and history of injury.16 Each joint has a specific ROM that is determined by the bony structures and musculature of the joint. Changes in the collagen fibers of the tendons and joint inflammation occur with age and account for some of the losses experienced over time. Repetitive use or disuse of muscles may also cause muscles to lengthen or shorten excessively. For example, sitting at a computer with head and shoulders slouched forward can limit one’s neck, back, and shoulder ROM (Figure 2-1).21
Epidemiology and Physical Activity 23 Figure 2-1. Sitting postures.
The mix of fat to nonfat tissues in the body is called body composition. Nonfat, or lean, tissues include the muscles, bones, and organs. There are multiple measures for body composition. It can be measured as a ratio of height to weight, called the body mass index (BMI), as the percentage of fat relative to the whole body, or by the taking the circumference of the abdomen. Obesity is defined as having a BMI greater than 3022 or having a body fat greater than 25% for men and 32% for women.23 The risk for chronic disease is greater in obese persons than those with normal body masses.24 However, the risk for overweight and obese people who are physically fit is similar to those of normal weight.25