BOX 3-1

Physical Activity and Physical Fitness

As noted in Chapter 1 (see the box titled “Key Terms Used in This Report” on p. 17), physical activity, a behavior, is defined as bodily movement that increases energy expenditure, whereas fitness is a physiologic trait, commonly defined in terms of cardiorespiratory capacity (e.g., maximal oxygen consumption), although other components of fitness have been defined (IOM, 2012b). Exercise, a subset of physical activity, is “planned, structured and repetitive” (Carpersen et al., 1985, p. 128) and designed to target a particular outcome, for example, cardiorespiratory capacity or another component of fitness. Physical education provides opportunities for developmentally appropriate physical activity, usually structured to promote motor skill development, fitness, and health.

The relationship between physical activity and physical fitness is complex and bidirectional. Numerous studies have shown a significant relationship between physical activity and cardiorespiratory fitness, which may mean that physical activity improves fitness or that physically fit individuals choose to engage in physical activity more than their less fit peers, or both. Experimental studies have shown that exercise training improves fitness (Malina et al., 2004), although the response is variable and clearly influenced by genetics (Bouchard, 2012), and physical activity and fitness are independently related to health and academic performance (see the figure below).


Conceptual framework illustrating relationships among physical activity, physical fitness, health, and academic performance.

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