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TABLE 1 Physical Activity Recommendations ADULT An average of 60 minutes per day of moderately intense physical activity (e.g., brisk walking or jogging at 3–4 mph) or shorter periods of more vigorous exertion (e.g., jogging for 30 minutes at 5.5 mph), in addition to activities identified with a sedentary lifestyle, was associated with a normal BMI range and is the amount of physical activity recommended for normal-weight adults. CHILDREN An average of 60 minutes of moderately intense daily activity is also recommended for children.

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PART II: PHYSICAL ACTIVITY 95 PHYSICAL ACTIVITY P hysical activity promotes health and vigor, and the lack of it is now a recognized risk factor for several chronic diseases. Observational and experimental studies of humans and animals have provided biologically plausible insights into the benefits of regular physical activity on the delayed progression of several chronic diseases, including cancer, cardiovascular dis- ease, Type II diabetes, obesity, and skeletal conditions. In addition, acute or chronic aerobic exercise may be related to favorable changes in anxiety, depres- sion, stress reactivity, mood, self-esteem, and cognitive functioning. Cross-sectional data from a doubly labeled water (DLW) database were used to define a recommended level of physical activity based on the physical activity level (PAL) that is associated with a normal body mass index (BMI) of 18.5–25 kg/m2. An average of 60 minutes per day of moderately intense physi- cal activity (e.g., brisk walking or jogging at 3–4 mph) or shorter periods of more vigorous exertion (e.g., jogging for 30 minutes at 5.5 mph), in addition to activities identified with a sedentary lifestyle, is the amount of physical activity recommended for normal-weight adults. An average of 60 minutes of moder- ately intense daily activity is also recommended for children. This amount of physical activity leads to an “active” lifestyle. Because the Dietary Reference Intakes are for the general healthy population, recommended levels of physical activity for weight loss of obese individuals are not provided. Historically, most individuals have unconsciously balanced their dietary energy intake and total energy expenditure due to occupation-related energy expenditure. However, occupational physical activity has significantly declined over the years. According to the 1996 Surgeon General’s Report on physical activ- ity and health, more than 60 percent of American adults were not regularly physically active and 25 percent were not active at all. This trend in decreased activity by adults is similar to trends seen in children who are less active both in and out of school. Physical activity and fitness objectives of the U.S. government’s Healthy People 2010 seek to increase the proportion of Americans who engage in daily physical activity to improve health, fitness, and quality of life. Similar recommendations to increase physical activity have been proposed in Canada. Excessive physical activity can lead to overuse injuries, dehydration and hyperthermia, hypothermia, cardiac events, and female athlete triad (loss of menses, osteopenia, and premature osteoporosis). To prevent adverse effects,

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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 96 previously sedentary people are advised to use caution when beginning a new activity routine. DETERMINING RECOMMENDATIONS Cross-sectional data from a DLW database were used to define a recommended level of physical activity for adults and children, based on the PAL associated with a normal BMI in the healthy range of 18.5 kg/m2 up to 25 kg/m2. PAL is the ratio of total energy expenditure (TEE) to basal energy expenditure (BEE). The data PAL categories were defined as sedentary (PAL ≥ 1.0 < 1.4), low active (PAL ≥ 1.4 < 1.6), active (PAL ≥ 1.6 < 1.9), and very active (PAL ≥ 1.9 < 2.5). Because an average of 60 minutes per day of moderate-intensity physical activities (or shorter periods of more vigorous exertion) provides a PAL that is associated with a normal BMI range, this is the amount of activity that is recom- mended for normal-weight individuals. For children, the physical activity rec- ommendation is also an average of 60 minutes of moderate-intensity daily ac- tivity. In terms of making a realistic physical activity recommendation for busy individuals to maintain their weight, it is important to recognize that exercise and activity recommendations consider “accumulated” physical activity. Box 1 provides examples of various physical activities at different intensi- ties. Additional examples of activity, along with instructions for keeping a weekly activity log, can be found in Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2002/2005). Special Considerations Pregnant women: For women who have been previously physically active, con- tinuing physical activities during pregnancy and postpartum can be advanta- geous. However, excessive or improper activity can be injurious to the woman and fetus. Appropriate physical fitness during pregnancy improves glucose tolerance and insulin action, improves emotional well-being, and helps prevent excessive weight gain. Fitness promotes a faster delivery, and the resumption of physical activity after pregnancy is important for restoring normal body weight. A full description of the benefits and hazards of exercise for the pregnant woman and fetus is beyond the scope of this publication. Women should consult with their physicians on how to safely exercise during pregnancy. Physical Activity Level and Energy Balance Increasing or maintaining an active lifestyle provides an important means for individuals to balance their energy intake with their total energy expenditure.

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PART II: PHYSICAL ACTIVITY 97 BOX 1 Examples of Various Physical Activities Mild (DPAL/hr: 0.05–0.10)a Billiards Canoeing (Leisurely) Dancing (Ballroom) Golf (with Cart) Horseback Riding (Walking) Loading/Unloading Car Playing Taking out Trash Walking (2 mph) Walking the Dog Watering Plants Moderate (DPAL/hr: 0.13–0.22) Calisthenics (No Weight) Cycling (Leisurely) Gardening (No Lifting) Golf (without Cart) Household Tasks, Moderate Effort Mopping Mowing Lawn (Power Mower) Raking Lawn Swimming (Slow) Vacuuming Walking (3–4 mph) Vigorous (DPAL/hr: 0.23–0.63) Chopping Wood Climbing Hills (No Load up to 5-kg Load) Cycling (Moderately) Dancing (Aerobic, Ballet, Ballroom, Fast) Jogging (10-Minute Miles) Rope Skipping Surfing Swimming Tennis DPAL/hr is the increase in PAL caused by the activity. a

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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 98 Changing one’s usual activity level can have a major impact on total energy expenditure and energy balance. The ultimate indicator of this energy balance is body weight, as seen through its maintenance or change. Energy intake and the energy expenditure of physical activity are control- lable variables that impact energy balance, in contrast to other uncontrollable variables that include age, height, and gender. During exercise, energy expendi- ture can increase far beyond resting rates, and the increased energy expenditure induced by a workout can persist for hours, if not a day or longer. Furthermore, exercise does not necessarily boost appetite or intake in direct proportion to activity-related changes in energy expenditure. HEALTHFUL EFFECTS OF PHYSICAL ACTIVITY Observational and experimental studies of humans and animals provide bio- logically plausible insights into the benefits of regular physical activity on the delayed progression of several chronic diseases, including cancer, cardiovascu- lar disease, Type II diabetes, obesity, and skeletal conditions. In addition, acute or chronic aerobic exercise may be related to favorable changes in anxiety, de- pression, stress reactivity, mood, self-esteem, and cognitive functioning. It is difficult to determine a quantifiable recommendation for physical ac- tivity based on reduced risk of chronic disease. However, meeting the physical activity recommendation of 60 minutes per day offers additional benefits in reducing the risk of chronic disease; for example, by favorably altering blood lipid profiles, changing body composition by decreasing body fat, and increas- ing muscle mass, or both. Endurance (Aerobic) Exercise Traditionally, the types of activities recommended for cardiovascular fitness are those of a prolonged endurance nature, such as bicycling, hiking, jogging, and swimming. Because of the energy demands associated with these pro- longed mild to moderate intensity endurance activities, they have the poten- tial to decrease body fat mass and preserve fat-free mass, thus changing body composition. Resistance Exercise and General Physical Fitness Although resistance training exercises have not yet been shown to have the same effects as endurance activities on the risks of chronic disease, their effects on muscle strength are an indication to include them in exercise prescriptions, in addition to activities that promote cardiovascular fitness and flexibility. Exer-

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PART II: PHYSICAL ACTIVITY 99 cises that strengthen the muscles, bones, and joints stimulate muscular and skeletal development in children, as well as assist in balance and locomotion in the elderly, thereby minimizing the incidence of falls and associated complica- tions of trauma and bed rest. EXCESSIVE PHYSICAL ACTIVITY Excessive physical activity can lead to the following adverse effects: • Overuse injuries: Too much or improper physical exercise can cause over- use injuries to muscles, bones, and joints, as well as injuries caused by accidents. In addition, pre-existing conditions can be aggravated by the initiation of a physical activity program. Activity-related injuries are of- ten avoidable but do occur and need to be resolved in the interest of long-term general health and short-term physical fitness. • Dehydration and hyperthermia: Exercise may cause dehydration, which can be aggravated by environmental conditions that increase fluid losses, such as heat, humidity, and lack of wind. People should consume water before, during (if possible), and after exercise. • Hypothermia: Hypothermia can result from water exposure and heat loss during winter sports. Poor choice of clothing during skiing, accidental water immersion due to a capsized boat, weather changes, or physical exhaustion may lead to the inability to generate adequate body heat to maintain core body temperature, which can lead to death, even when temperatures are above freezing. • Cardiac events: Although regular physical activity promotes cardiovas- cular fitness, heavy physical exertion can trigger the development of arrhythmias or myocardial infarctions or, in some instances, can lead to sudden death. • Female athlete triad: Athletic women who undereat or overtrain can de- velop a condition, or cluster of conditions, called the “female athlete triad.” In this triad, disordered eating and chronic energy deficits can lead to loss of menses, osteopenia, and premature osteoporosis, increas- ing the risk of hip, spine, and forearm fractures. Prevention of Adverse Effects Previously sedentary people are advised to begin a new activity routine with caution. The following people should seek medical evaluation, as well as clini- cal exercise testing, clearance, and advice prior to starting an exercise program: men over age 40 years, women over age 50 years, people with pre-existing

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DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 100 medical conditions, and people with known or suspected risk factors or symp- toms of cardiovascular and other chronic diseases (physical inactivity being a risk factor). For those with cardiovascular risk or orthopedic problems, physi- cal activity should be undertaken with professional supervision. For all indi- viduals, easy exercise should be performed regularly before more vigorous ac- tivities are conducted.

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PART II: PHYSICAL ACTIVITY 101 KEY POINTS FOR PHYSICAL ACTIVITY Lack of physical activity and obesity are now recognized risk 3 factors for several chronic diseases. Observational and experimental studies of humans and animals 3 provide biologically plausible insights into the benefits of regular physical activity on the delayed progression of several chronic diseases, including cancer, cardiovascular disease, Type II diabetes, obesity, and skeletal conditions. Acute or chronic aerobic exercise may be related to favorable 3 changes in anxiety, depression, stress reactivity, mood, self- esteem, and cognitive functioning. Changing one’s usual activity level can have a major impact on 3 total energy expenditure and energy balance. In addition to activities that characterize a sedentary lifestyle, 3 an average of 60 minutes per day of moderate-intensity physical activities (e.g., brisk walking or jogging at 3–4 mph) or shorter periods of more vigorous exertion (e.g., jogging for 30 minutes at 5.5 mph) is the amount of physical activity recommended for normal-weight adults. For children, the physical activity recommendation is also an average of 60 minutes of moderate-intensity daily activity. More than 60 percent of American adults are not regularly 3 physically active and 25 percent are not active at all. Similar trends are seen in children. Excessive physical activity can lead to overuse injuries, 3 dehydration and hyperthermia, hypothermia, cardiac events, and female athlete triad (loss of menses, osteopenia, and premature osteoporosis). Previously sedentary people are advised to begin a new activity 3 routine with caution to prevent adverse effects.