This issue of JAMA includes a summary of the new Physical Activity Guidelines for Americans, 2nd edition. These guidelines update those presented in 2008 and expand the medical conditions for which physical activity is likely beneficial.
Paul D. Thompson MD, Thijs M. H. Eijsvogels PhD, JAMA Network November 12, 2018
The final recommendations are based on a systematic literature review by a committee of exercise and health experts and include only those recommendations judged to have strong, or moderately strong, scientific support. Achieving the guideline-recommended levels of physical activity will be difficult for the entire nation, given that approximately 80% of US adults and adolescents do not presently accumulate sufficient physical activity for optimum health.
Efforts to increase physical activity among people in the United States will require the cooperation of many sectors of society including clinicians, other health care professionals, and health care organizations. Achieving these recommendations will substantially improve individual and population health. So what are the key messages for clinicians, and what should clinicians tell patients?
Probably the most important message from the 2018 guidelines is that the greatest health benefits accrue by moving from no, to even small amounts of, physical activity, especially if that activity is of moderate (eg, brisk walking) or vigorous (eg, jogging and running) intensity. Multiple studies demonstrate that the steepest reduction in disease risk, such as for coronary heart disease, occurs at the lowest levels of physical activity.
Patients need to understand that even small amounts of physical activity are beneficial and that reductions in the risk of disease and disability occur by simply getting moving. The evidence demonstrates that adults obtain the maximal benefits of physical activity by regularly performing 150 to 300 minutes per week of moderate-intensity or 75 to 150 minutes per week of vigorous-intensity activity or an equivalent combination of moderate- and vigorous-intensity aerobic activity. These levels of activity are possible for most healthy people.
The new guidelines also provide evidence that even brief bouts of physical activity are beneficial. Prior guidelines suggested that bouts of at least 10 minutes’ duration were required, but the present guidelines suggest there is no threshold of benefit and that even short-duration activities such as climbing a flight of stairs are beneficial. The key point for patients is that large health benefits accrue from even small amounts of physical activity and that even short-duration activity lasting less than 10 minutes is beneficial.
Patients should be reassured that they do not need large amounts of time or complex exercise regimens to be healthier. Any activity is better than none. It is also possible to perform all activities on 1 or 2 days per week, because this yields health benefits similar to those achieved through activity on 3 or more days per week.
Another important message for patients and clinicians is that some of the health benefits of physical activity are acute effects produced by recent exercise. It has long been known that a single exercise session acutely reduces blood pressure in men with hypertension for up to 13 hours after moderate-to-vigorous exertion.  
Similarly, a single exercise session reduces triglyceride levels and improves insulin sensitivity measured 24 hours after exertion.  The magnitude of these effects depends on the amount and intensity of exercise so that the effects are small in physically unfit individuals because of their inability to tolerate high or intense exercise workloads, but these acute effects can be considerable in healthy individuals, especially in trained athletes. Consequently, patients need to know that they do not need to “get into shape” to benefit from physical exertion, although these acute exercise effects increase as they are able to exercise more.
The new guidelines provide recommendations on the amount and type of physical activity for virtually all people and patient groups because of evidence that nearly all groups achieve health benefits from physical activity. Preschool children aged 3 through 5 years are encouraged to be physically active throughout the day.
Children and adolescents aged 6 through 17 years should perform at least 60 minutes of moderate-intensity to vigorous-intensity physical activity daily. The recommended levels of physical activity for adults (150-300 minutes of moderate-intensity or 75-150 minutes of vigorous-intensity activity weekly) should be supplemented by 2 sessions of resistance or muscle-building exercise.
Older individuals should follow the adult aerobic and strength activity recommendations but include exercises to enhance balance, since such activity decreases fall risk. Even individuals in their 90s can improve their quadriceps muscle strength with appropriate exercise training, demonstrating that it is never too late to use physical activity to help ensure that older adults do not outlive their muscles.
An examination of the evidence for the utility of physical activity during pregnancy and the postpartum period was not part of the committee’s original charge. This topic was added later, and the committee found sufficient evidence to recommend that pregnant and postpartum women should accrue 150 minutes weekly of moderately intense aerobic activity. Individuals with chronic health conditions and disabilities should also attempt to achieve the levels of physical activity recommended for adults. These recommendations demonstrate that a broad range of patient groups can benefit from increased physical activity. The message for clinicians is that an assessment and plan for physical activity should be part of most patients’ management.
The health benefits of physical activity are also broad and listed in the summary in the guidelines. Benefits in adults include reduced risk for all-cause and cardiovascular mortality, cardiac and cerebrovascular events, hypertension, type 2 diabetes, lipid disorders, and cancer of the bladder, breast, colon, endometrium, esophagus, kidney, stomach, and lung.
Physical activity alone is not an effective weight loss strategy for most people because of the prodigious volume of exercise required to expend sufficient calories to lose weight, but physical activity slows the rate of weight regain with aging, contributes to weight loss with caloric restriction, and helps prevent weight gain after weight loss. Many of these benefits are well known, but less appreciated is the evidence that physical activity improves cognition and sleep and reduces anxiety and the risk of depression and dementia.
The point for clinicians is that physical activity should be strongly considered as primary or adjunctive therapy for many common clinical conditions such as mild depression, anxiety, and sleep difficulties. How muscular activity produces these health effects is reasonably well-defined for some conditions such as hypertriglyceridemia  and reduced glucose uptake. The mechanisms for beneficial effects on systems not directly affected by physical activity are less clear but may be mediated by the release of cytokines (“myokines”)  and exosomes  from skeletal muscle during activity.
Skeptics of the benefits of physical activity can argue that these guideline recommendations lack the high-quality evidence provided by randomized clinical trials. This is only partly true. Many of the risk factors for cardiovascular diseases, for example, have been examined in clinical trials. Similarly, there are multiple randomized clinical trials of exercise-based cardiac rehabilitation. Most trials were too small to individually demonstrate benefit, but collectively they do demonstrate a 26% relative reduction in cardiovascular mortality.
There is unlikely to ever be a placebo-controlled clinical trial of physical activity in the healthy population—the required sample size would be prohibitively large or the duration prohibitively long. Skeptics also can argue that the ability or desire to be physically active is somehow genetically determined. Most developed societies have become sedentary only over the last century—too short a time for such rapid evolution. Even recent history demonstrates that, as with earlier generations, almost everyone can become more physically active.
Clinicians and other health care professionals should have a major role in this “call to activity.” The clinical examination should routinely include an assessment of physical activity. Indeed, several nationally respected health care systems, including Kaiser Permanente and Intermountain Healthcare, now include physical activity as a fifth vital sign during patient examinations. This both shows the patient that physical activity is important to the clinician and helps to identify inactive patients, a group who can benefit the most.
Clinicians and other health care practitioners need to encourage physical activity in their patients but also encourage physical activity opportunities in workplaces, schools, and communities. Clinicians also must avoid being a barrier to physical activity because of concerns about the cardiovascular and orthopedic risks of increased activity.
Both risks are extremely small with gradually progressive physical activity. Physicians and other educators in academic health care centers should ensure that there is sufficient training about the benefits of exercise and physical activity to make future practitioners comfortable with prescribing exercise as an important component of a healthy life.
Physical activity has been described by Morris, a pioneering exercise epidemiologist and lead investigator of the London Transport Workers Study, as “the best buy in public health.”  Clinicians cannot afford to allow patients to miss out on this inexpensive path to healthier lives.
New Physical Activity Guidelines A Call to Activity for Clinicians and Patients, JAMA. Published online November 12, 2018. doi:10.1001/jama.2018.16070
Source JAMA Network
New HHS Guideline on Physical Activity for Americans in Medscape
Physical Activity Guidelines for Health and Prosperity in the United States in JAMA Network
Physical Activity Should be a Vital Sign of Children’s Overall Health in American Academy of Pediatrics