Obesity represents a significant public health concern with one-third of adults classified as living with obesity in the United States and correlates with cardio-metabolic comorbidities that can decrease the quality of life.[1][2] Researchers have proposed that exercise is an important lifestyle measure to maintain a healthy weight. This review will cover the role of exercise in obesity and fitness.

Obesity is an excessive fat accumulation in adipose tissues and defined by a body mass index (BMI) 30 kg/m2 and above. Individuals in the BMI range of 25 to 30 kg/m2 are categorized as overweight while a BMI of 40 kg/m2 and above is morbidly obese.[3] Obesity correlates with increasing an individual’s risk of cancers, stroke, metabolic disease, heart failure, and other cardiovascular conditions [4][5][6], highlighting the need to reduce incidence and prevalence of obesity. Chronic low-grade inflammation associated with obesity is hypothesized to have associations with the adverse cardio-metabolic side effects.[7] Although short term inflammation is beneficial to initiate an immune response, chronically elevated levels of inflammation exhaust the immune system and contribute to immune dysfunction.[2] Researchers posit that this inflammation is stimulated by the excess adipose tissue, which has consistently shown to play a role as an active endocrine organ.[8]

Reducing adipose tissue is one of the ways to reduce weight in individuals with obesity, and is necessary to mitigate negative cardio-metabolic co-morbidities in obesity. Two methods exist that can effectively decrease adipose tissue and include: 

1. Dietary modification 

2. Energy expenditure modification (i.e., exercise)

Thus, increasing energy expenditure can help reduce excess adipose tissue and obesity. The current guidelines put out by the American College of Sports Medicine (ACSM) include either aerobic or anaerobic exercise. Aerobic exercise (i.e., running, cycling, rowing, etc.) is an exercise that exhausts the oxygen in the muscles, but oxygen consumption is sufficient to supply the energy demands placed on the muscles and does not need to derive energy from another source.[9] On the other hand, anaerobic exercise (or resistance exercise, i.e., weight lifting) is oxygen consumption that is not sufficient to supply the energy demands placed on the muscles, and your muscles must break down other energy supplies, such as sugars, to produce energy and lactic acid.[9] Physical activity (PA), is included in the exercise, although it does not necessarily include structured exercise plans/sessions.

The measurement of exercise is conducted in “metabolic equivalent tasks” (METs), which roughly equate to the effort and energy expenditure it takes for an individual to sit quietly. Physical activity is frequently incorporated into different lifestyle interventions, highlighting the need for regular amounts of physical activity throughout the day. Physical activity in the general lifestyle includes goal setting, problem-solving, leisure-time physical activity, and activity used for commuting. Outcomes of interest include cardiorespiratory fitness, body composition, and muscular fitness. Recently, much literature has shown the positive effects of exercise on not only physical health but also cognitive and emotional well-being in people of all ages.[10]

Overweight and obese people can partake in the same exercise prescriptions as individuals with normal weight. However, special considerations must be made, such as current co-morbidities that may be associated with obesity like orthopedic risk (i.e., arthritis), pulmonary, and/or cardiac co-morbidities. However, this should not deter individuals away from participating in exercise programs, as exercise is extremely important for overall health.[11][12] Currently, there are several exercise guidelines for individuals living with obesity and include the American College of Sports Medicine (ACSM), the Obesity Medical Association (OMA), and the Obesity Society (TOS), which are all clinically available to aid individuals in prescribing exercise. Here, we outline the general recommendations for individuals living with obesity as follows:

A. Patients must be cleared by their healthcare provider for any comorbid conditions by history and physical examination to maximize patient safety.[13] Examples include the Physical Activity Readiness Questionnaire (PAR-Q) and Health/Fitness Facility Preparticipation Screening Questionnaire.[14][15]

B. Minimum of 150 to 300 minutes of moderate physical activity per week or 75 to 150 minutes of vigorous physical activity weekly is essential to prevent weight regain, increase weight loss and improve fitness.[14] However, for individuals who wish to lose weight, at least 200 to 300 minutes of moderate to vigorous physical activity each week is recommended to encourage long-term weight loss.[14][15]

1. The recommendation for inactive individuals is “start low and go slow” by starting with lower intensity activities and gradually increasing frequency and duration of the activity. 
2. It is a good idea to spread out aerobic activity over the week, versus all the time in one day.
3. Utilize appropriate gear and sports equipment and chose safe environments. 
4. Adjust exercises as necessary to decrease orthopedic risk or is non-ambulatory (if applicable). This can include cycling instead of running if an individual has arthritis. If individuals are not ambulatory or may have to modify exercise due to special circumstances, the exercise guidelines still apply. However, the patient can get creative to find ways to achieve them, such as utilizing limbs that are more ambulatory than others (e.g., moving arms faster in order to get the heart rate up if legs are not able to be used, upper body ergometer, etc.)
5. Anaerobic training can be implemented and may even increase muscle mass. Anaerobic exercise has not been shown to be effective in altering energy expenditure or absolute weight loss.[13] However, if the goal of the patient is to increase muscle mass, then anaerobic exercise is highly encouraged. Furthermore, in order to increase muscle mass, each muscle group should be exercised at a minimum of 10 sets per week, with one set consisting of 8 to 10 reps. Also, ensure proper form to avoid injuries. Individuals who are not ambulatory or may have limited movement are still able to participate in an anaerobic exercise. Individuals must ensure proper form but can modify exercises as needed, such as upper body only exercises, lower body only exercises, using a neutral grip, keeping stable movements, etc.).

Utilizing exercise as a means of reducing obesity (i.e., reducing fat mass) has benefits beyond the reduction of fat mass. Fitness is associated with more desirable clinical outcomes in many instances, such as decreasing metabolic disease [14], cardiovascular disease [15], Alzheimer disease risk, inflammation [16], and many other disease states not listed here. 

Exercise/physical activity is a proven modality for treating the disease of overweight and obesity. However, management of this disease is best through dietary interventions and regular exercise. Exercise is an integral part of not only weight loss, but overall health as well.  A balanced hypocaloric diet, aerobic training, cognitive behavioral therapy (CBT) are helpful in reducing weight. Weight reducing pharmacotherapy is indicated in individuals with a BMI greater than 30 kg/m2 with or without comorbidities. Surgery (Bariatric) is only needed in reducing weight in BMI greater than 40 kg/m2, especially with comorbidity.

The Food Drug Administration (FDA) approved medications and their mechanism of action:

• Orlistat - Inhibits pancreatic gastric lipase
• Phentermine/topiramate combination - unknown, believed to inhibit Norepinephrine (NE) release and GABA gamma-aminobutyric acid transmission
• Bupropion/naltrexone combination - NE/Dopamine Reuptake Inhibitor (NDRI), Naltrexone is an opioid antagonist
• Liraglutide - Glucagon-like peptide- GLP-1 agonist, decreases dipeptidyl peptidase-IV metabolism and appetite.

It is important to know that aerobic exercise is the only form of physical activity that has been proven to be efficacious in the management of obesity. Recommended is moderate to high-intensity aerobics involving larger groups of muscles. It should be practiced for a long duration to appreciate the effect. Hence a weekly aerobic exercise of at least 150 -180 minutes can increase physical fitness. Resistance exercise has also been shown to have some meaningful impact on weight.[17][18][19][20][21]