Physical Activity Treatment

Seth A. Creasy

Danielle Marie Ostendorf

Victoria A. Catenacci

CLINICAL SIGNIFICANCE

Increasing physical activity is recognized as a significant, modifiable risk factor for the prevention and treatment of overweight and obesity. In 2018, the US Department of Health and Human Services published the second edition of the Physical Activity Guidelines (PAG) for Americans, which provides scientific evidence of the benefits of physical activity.¹ There were four main recommendations for US adults (see Table 6.1). Importantly, the PAG recommend ≥150 to 300 minutes/week of moderate-intensity aerobic activity or ≥75 to 150 minutes/week of vigorous-intensity aerobic activity and muscle strengthening activities at least two times per week for overall health benefits. The PAG also recognize that higher levels of aerobic activity (≥300 minutes/week of moderate-intensity aerobic activity or ≥150 minutes/week of vigorous-intensity aerobic activity) are associated with additional health benefits including prevention of weight gain and regain following weight loss.² However, in 2018, only 54.2% (53.2% to 55.3%) of adults nationwide self-reported achieving the minimum aerobic threshold of ≥150 minutes/week of moderate-intensity physical activity or ≥75 minutes of vigorous-intensity physical activity and even fewer adults, 37.4% (36.4% to 38.4%), reported achieving ≥300 minutes/week of moderate-intensity physical activity or ≥150 minutes/week of vigorous-intensity aerobic activity.³ Individuals with obesity engage in even lower amounts of physical activity compared with adults without obesity. It is difficult to determine the extent to which low levels of physical activity precede the development of obesity diagnosis or whether the presence of obesity limits an individual’s ability to engage in physical activity.

Health Benefits of Physical Activity

There is extensive literature outlining the benefits of regular physical activity for individuals with and without obesity. Physical activity helps to lower risk for CVD, hypertension, type 2 diabetes (T2D), and some cancers.¹ An increase from being inactive to achieving 150 minutes/week of moderate-intensity physical activity is associated with a 34% lower risk for CVD mortality, a 21% lower incidence of CVD, and a 27% lower incidence of T2D.⁴ A meta-analysis of cohort studies found a 14% reduction in risk for all-cause mortality associated with engaging in 150 minutes/week of moderate-to-vigorous physical activity (MVPA) and a 26% reduction in risk for mortality associated with engaging in 300 minutes/week of MVPA.⁵ In addition, there are other benefits of physical activity such as providing opportunities to have fun, be with friends and family, and enjoy the outdoors.

Consequences of Sedentary Behavior and Inactivity

Sedentary behavior is defined as any behavior during waking hours characterized by low energy expenditure, while in a sitting, reclining, or lying posture.⁶ Common sedentary behaviors include watching television, playing video games, using a computer, and driving a car. On average, Americans spend ˜55% (7.7 hours/day)
of their waking hours engaged in sedentary behaviors.⁷ Studies have shown a link between sedentary behaviors and increased rates of obesity, independent of the overall level of physical activity.⁸,⁹,¹⁰ Higher levels of sedentary behavior are also associated with greater risk for all-cause mortality, CVD, CVD mortality, T2D, and cancers of the colon, endometrium, and lung.¹ Thus, both increasing physical activity and decreasing sedentary behavior are important for overall health. As illustrated in Figure 6.1, the risk of all-cause mortality is associated with both behaviors. To summarize this figure, individuals would benefit from making efforts to increase levels of MVPA as well as decreasing sitting time.

TABLE 6.1 Summary of Key Recommendations From the 2018 Physical Activity Guidelines for Americans

KEY RECOMMENDATIONS

1. Adults should move more and sit less throughout the day. Some physical activity is better than none. Adults who sit less and do any amount of moderate-to-vigorous physical activity gain some health benefits.

2. For substantial health benefits, adults should do at least 150 minutes (2 hours and 30 minutes) to 300 minutes (5 hours) a week of moderate-intensity aerobic physical activity, or 75 minutes (1 hour and 15 minutes) to 150 minutes (2 hours and 30 minutes) a week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate-intensity and vigorous-intensity aerobic activity. Preferably, aerobic activity should be spread throughout the week.

3. Additional health benefits are gained by engaging in physical activity beyond the equivalent of 300 minutes (5 hours) of moderate-intensity physical activity a week.

4. Adults should also do muscle strengthening activities of moderate or greater intensity and that involve all major muscle groups on 2 or more days a week, as these activities provide additional health benefits.

Physical inactivity, which is distinct from sedentary behavior, is defined as a lack of any MVPA (see Table 6.2) beyond basic movement from daily activities. Physical inactivity is considered the fourth leading risk factor for death due to noncommunicable disease worldwide and contributes to >3 million preventable deaths annually. In sum, overwhelming evidence supports the benefits of regular physical activity and the negative consequences of inactivity and sedentary behavior. Current PAG (see Table 6.1) focus not only on increasing physical activity but also on making an effort to sit less. Thus, a simple message to “move more and sit less” can summarize this information succinctly for patients.

FIGURE 6.1 Relationship between moderate-to-vigorous physical activity (MVPA), sitting time, and risk of all-cause mortality in adults. Having high amounts of sitting time concomitantly with low amounts of MVPA is associated with the highest risk of all-cause mortality (indicated in red in upper left corner). As one increases MVPA, the risk associated with high amounts of sitting begins to decrease (indicated by orange color). Engaging in high amounts of MVPA is associated with lower risk of all-cause mortality even when combined with high amounts of sitting (indicated by green in the upper right corner). At the lowest levels of MVPA and the lowest levels of sitting time, there is still increased risk of all-cause mortality (indicated by orange in lower left corner). Risk of mortality increases with increased sitting. The highest levels of MVPA and lowest levels of sitting time are associated with the lowest risk of all-cause mortality (indicated by green in lower right corner). (Adapted from Physical Activity Guidelines Advisory Committee. 2018 Physical Activity Guidelines Advisory Committee Scientific Report. U.S. Department of Health and Human Services; 2018. Adapted from data from Ekelund U, Steene-Johannessen J, Brown WJ, et al. Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women. Lancet. 2016;388(10051):1302-1310.)

REVIEW OF EVIDENCE FOR PHYSICAL ACTIVITY IN OBESITY TREATMENT

Physical Activity and Weight Gain Prevention

Epidemiological data suggest that adults tend to gain an average of 1 to 2 pounds of body weight per

year.¹¹ This annual weight gain places individuals at an increased risk for becoming overweight or obese with age. Physical activity has been postulated as a potential strategy for either attenuating or preventing this age-related weight gain. Several prospective, observational studies provide evidence that engaging in regular physical activity helps to prevent weight gain.¹² Randomized trials have also examined the relationship between physical activity and weight gain with most studies suggesting that engaging in moderate-intensity physical activity is sufficient to prevent weight gain.¹² In a study by Church et al., postmenopausal women who engaged in three different doses of supervised moderate-intensity aerobic activity (approximately 72, 136, and 194 minutes/week) over 6 months lost 3.0, 4.6, and 3.3 lb of body weight, respectively, compared with a 2 lb weight loss in the nonactive control group.¹³ In a similar study, McTiernan et al. found that men and women who participated in a facility-based and home-based physical activity program over 1 year lost 3.0 and 4.0 lb compared with 0.2 and 1.5 lb weight gain in nonactive controls.¹⁴ The combination of these studies and others suggest that a dose of approximately 150 to 250 minutes/week of moderate-intensity aerobic activity is effective for preventing weight gain and potentially eliciting modest weight loss.

TABLE 6.2 Physical Activity and Exercise Terminology

TERMS	DEFINITION
Metabolic equivalents (METs)	A method of standardizing the intensity of an activity. This method is based on the energy cost of an activity. 1 MET is equivalent to the resting energy expenditure. 3 METs, which is considered moderate-intensity physical activity, means that the activity elicits an energy cost that is threefold resting energy expenditure.
Aerobic activity	Activities where the energy demand is met via aerobic pathways; also known as cardiovascular activities; typically associated with increases in breathing and heart rate.
Strength/resistance activity	A form of physical activity that focuses on muscular contraction and seeks to improve muscular strength and endurance. Typically done for shorter periods of time compared with aerobic activity.
Rating of perceived exertion (RPE)	The perceived intensity of an activity. Usually rated on a 0-10 scale. Moderate intensity is typically associated with an RPE of 3-5.
Sedentary behavior	Time spent awake with a low energy expenditure (<1.5 METs) in a sitting/reclining posture. Examples: watching TV, desk work, driving
Light physical activity	Activities where heart rate is not elevated much above resting (≥1.5-<3.0 METs). Examples: normal daily activity, intermittent periods of normal walking, some forms of yoga
Moderate physical activity	Activities where heart rate is moderately elevated (50%-70% of maximum heart rate); ≥3.0-<6.0 METs. Examples: brisk walking, cycling <10 miles/hour, water aerobics
Vigorous physical activity	Activities where heart is elevated (70%-85% of maximum heart rate); ≥6.0 METs. Examples: running, swimming, cycling >10 miles/hour
Moderate-to-vigorous physical activity	Any activity ≥3.0 METs. Commonly used in public health recommendations. This is a summary measure that includes both moderate and vigorous physical activity
Dose/volume	The total dose or volume of activity is usually a summary of weekly activity. For overall health benefits, the dose of physical activity should progress up to 300 minutes/week. For weight loss and weight loss maintenance, even higher amounts of physical activity may be necessary. Energy expenditure per week: Physical activity and exercise can be prescribed based on the energy expenditure of activity. This type of prescription is difficult and requires careful measurements. It is typically done in controlled research studies. MET-minutes per week: This prescription takes into account the intensity and duration of physical activity. The MET value of each activity is multiplied by the duration of the activity. Measuring physical activity as MET-min is typically done in research studies only.

Physical Activity Alone for Weight Loss

It has long been believed that increasing physical activity leads to increased energy expenditure and subsequent weight loss. Between 2013 and 2016, ˜63% of the US adults who attempted to lose weight reported using exercise as a primary strategy.¹⁵ Despite its frequent use as a weight loss strategy, physical activity alone typically results in only modest weight loss. Several well-designed prospective intervention trials have shown that prescribing physical activity alone (i.e., without dietary modification) typically produces weight losses of 1% to 3%.¹² Furthermore, the changes in body weight observed in these studies are on average only ˜30% of predicted based upon the expected energy expenditure of the activity prescription. This is true even when exercise is supervised and adherence to physical activity is carefully monitored. Studies have also shown marked interindividual variability in weight loss in response to exercise, with some individuals losing substantial amounts of weight and others gaining weight. Recent studies suggest that a subset (˜50%) of individuals may “compensate” for the increase in physical activity with increased energy intake and/or increased sedentary behavior and thereby lose less weight than expected. A recent study found that compensation to supervised physical activity was largely due to increases in energy intake rather than increases in sedentary behavior.¹⁶ In addition, individuals who compensated had increased hunger and cravings for sweets. Thus, compensation and nonadherence mitigate the beneficial effects of physical activity on body weight in some individuals.

Despite the number of studies demonstrating relatively modest weight loss from physical activity alone, a few studies have shown that physical activity alone, when dosed in high amounts and supervised, results in clinically significant (≥5%) weight loss.¹² For example, when men and women engaged in 225 minutes of supervised physical activity per week for 16 months, men reduced body weight by 11.4 lb (˜5%) more than nonactive controls and women had 5.0 lb (˜3%) less weight gain compared with nonactive controls.¹⁷ This large difference in weight change in men versus women was believed to be due to sex differences in physical activity energy expenditure. Notably, engaging in physical activity at the same intensity for the same duration would likely lead to higher energy expenditure during physical activity sessions for men compared with women due to their larger body size. Additional studies suggest that high volumes of physical activity can elicit weight loss of ≥5% in men and women when dosed based on energy expenditure rather than exercise duration. In addition, there appears to be a dose-response relationship with more physical activity energy expenditure being associated with greater weight loss.

In summary, engaging in ≥150 minutes/week of MVPA will elicit modest (1% to 3%) weight loss on average; however, higher amounts of MVPA (≥250 minutes/week) are needed to elicit clinically significant (≥5%) weight loss. Weight loss with physical activity is typically less than predicted from the energy expended in activity due to compensatory changes in eating and nonexercise activity behaviors, and there is considerable variability in weight change in response to physical activity alone. Future research is needed to understand strategies to reduce compensation and make physical activity alone a more effective weight management strategy.

Physical Activity Combined With Dietary Restriction for Weight Loss

Most behavioral weight loss interventions encourage individuals to increase physical activity in combination with an energy-reduced diet.¹⁸ These interventions also employ behavioral support in order to maximize adherence to these recommendations. If the reduced energy diet severely restricts calories (i.e., >800 to 1,000 kcal/day deficit), similar weight losses are observed between a diet plus physical activity program and a diet-only program.¹² However, several studies have found that the combination of a more modest energy-reduced diet (i.e., 500 to 750 kcal/day deficit) and physical activity produces greater weight loss than diet alone.¹² A
systematic review of studies lasting ≥12 months found that diet plus physical activity resulted in a mean weight loss of 8.8% compared with a weight loss of 6.9% from diet alone.¹⁹

Physical Activity and Weight Loss Maintenance

High levels of physical activity, and more specifically MVPA, are consistently and positively associated with long-term weight loss and weight loss maintenance success.¹²,²⁰,²¹ One study found that individuals who maintained a weight loss of >10% at 18 months engaged in an amount of physical activity equivalent to brisk walking for ˜260 minutes/week²⁰ or approximately 10,000 steps per day.²² Importantly, ˜35% of their total steps were at a moderate-to-vigorous intensity and were taken in bouts ≥10 minutes. In a recent cross-sectional study, successful weight loss maintainers (WLMs, individuals maintaining a weight loss of >30 lb for >1 year) engaged in a total of 665 minutes/week of MVPA with 272 minutes of MVPA accumulated in bouts ≥10 minutes.²¹ In addition, WLMs engaged in ≥60 minutes of MVPA on 73% of days of the week suggesting they achieve high levels of activity with consistency across the week. These and other studies²³ suggest that WLMs maintain their body weight by engaging in high amounts of physical activity, thereby allowing them to eat a similar amount of calories as they were consuming prior to weight loss.

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