Lack of exercise is a major cause of chronic diseases
Chronic diseases are major killers in the modern era. Physical inactivity is a primary cause of most chronic diseases. The initial third of the article considers: activity and prevention definitions; historical evidence showing physical inactivity is detrimental to health and normal organ functional capacities; cause vs. treatment; physical activity and inactivity mechanisms differ; gene-environment interaction [including aerobic training adaptations, personalized medicine, and co-twin physical activity]; and specificity of adaptations to type of training. Next, physical activity/exercise is examined as primary prevention against 35 chronic conditions [Accelerated biological aging/premature death, low cardiorespiratory fitness (VO2max), sarcopenia, metabolic syndrome, obesity, insulin resistance, prediabetes, type 2 diabetes, non-alcoholic fatty liver disease, coronary heart disease, peripheral artery disease, hypertension, stroke, congestive heart failure, endothelial dysfunction, arterial dyslipidemia, hemostasis, deep vein thrombosis, cognitive dysfunction, depression and anxiety, osteoporosis, osteoarthritis, balance, bone fracture/falls, rheumatoid arthritis, colon cancer, breast cancer, endometrial cancer, gestational diabetes, preeclampsia, polycystic ovary syndrome, erectile dysfunction, pain, diverticulitis, constipation, and gallbladder diseases].
The article ends with consideration of deterioration of risk factors in longer-term sedentary groups; clinical consequences of inactive childhood/adolescence; and public policy. In summary, the body rapidly maladapts to insufficient physical activity, and if continued, results in substantial decreases in both total and quality years of life. Taken together, conclusive evidence exists that physical inactivity is one important cause of most chronic diseases. In addition, physical activity primarily prevents, or delays, chronic diseases, implying that chronic disease need not be an inevitable outcome during life.
1. Organization of article
1.1 Entire article
An underappreciated primary cause of most chronic conditions is the lack of sufficient daily physical activity (“physical inactivity”). Overwhelming evidence proves the notion that reductions in daily physical activity are primary causes of chronic diseases/conditions and that physical activity/exercise is rehabilitative treatment (therapy) from the inactivity-caused dysfunctions. The general strategy of presentation divides the article into three major sections: 1) Conceptual information forming the foundation to understand the remaining article; 2) Primary literature supporting physical inactivity as a primary cause to a myriad of chronic conditions/diseases, and 3) additional considerations. The aim of the entire article is to bring better understanding and insight into the observation that a lack of physical activity at ancestral levels initiates 35 pathological and clinical conditions.
1.2 First third of article
Conceptual information is presented in five parts in the first third of the article. 1) Definitions of forms of physical activity, functional capacity, types of fitness, chronic diseases, types of prevention so that the reader understands how the article employs these words; 2) A brief chronology of the three-millennia history that recognizes that physical inactivity reduces functional capacity and health; 3) Cause vs. treatment are discussed to emphasize that physical inactivity is a primary cause of chronic conditions/diseases; 4) Growing evidence that mechanisms by which inactivity causes disease differ from mechanisms by which physical activity is a therapy/treatment to act as a primary preventer of disease; and 5) Gene-environment interactions have varying degrees of gene involvement in the magnitude of change to physical activity.
1.3 Center portion of article
Physical inactivity is a primary cause initiating 35 separate pathological and clinical conditions. Many of the 35 conditions are subdivided under major categories, such as loss of functional capacities with chronological aging; metabolic syndrome, obesity, insulin resistance, prediabetes/type 2 diabetes, non-alcoholic liver disease, cardiovascular diseases, cognitive functions and diseases, bone and connective tissue disorders, cancer, reproductive diseases, and diseases of digestive tract, pulmonary, and kidney.
1.4 Final portion of article
The article ends with considerations of clinical significance, increasing risk factors during long-term sedentarism, the developmental and clinical consequences of inactive childhood/adolescence, and policy.
2.1 CDC definitions of forms of physical activity
Verbatim definitions for exercise and health are from the US Centers for Disease Control and Prevention (CDC) are used where possible due to the authority they carry (90). US governmental definitions were selected for the article to provide the framework for this article’s discussions of how 1) exercise/physical activity prevents chronic diseases and 2) lack of physical activity is a primary event that causes chronic diseases.
“A subcategory of physical activity that is planned, structured, repetitive, and purposive in the sense that the improvement or maintenance of one or more components of physical fitness is the objective”, as defined by CDC (90).
“Physical activity performed during leisure time with the primary purpose of improving or maintaining physical fitness, physical performance, or health”, as defined by CDC (90).
“Any bodily movement produced by the contraction of skeletal muscle that increases energy expenditure above a basal level. Physical activity generally refers to the subset of physical activity that enhances health”, as defined by CDC (90).
“A human condition with physical, social and psychological dimensions, each characterized on a continuum with positive and negative poles”, as defined by CDC (90).
Health-enhancing physical activity
“Activity that, when added to baseline activity, produces health benefits. Brisk walking, jumping rope, dancing, playing tennis or soccer, lifting weights, climbing on playground equipment at recess, and doing yoga are all examples of health-enhancing physical activity”, as defined by CDC (90).
As previously stated, this article will concentrate on the use of physical activity to prevent physical inactivity, and, thus, prevent many chronic diseases.
2.2 Definition of physical inactivity
CDC definitions for exercise do not include a definition of “physical inactivity”. We define physical inactivity as “physical activity levels less than those required for optimal health and prevention of premature death”. Further consideration of the definition is given in section entitled, “Prevention of death by primary prevention of physical inactivity”.
2.3 Definition of functional capacity
We define “functional capacity” as the ability of a cell, organ, system, or body to maintain homeostasis within their narrow limits of survival in response to a specified stress. If an external stress disrupts homeostasis beyond an organism’s functional capacity, life may not be sustained. Diminished ability to adapt to stressors increases the likelihood of death. Functional capacity is pliable; declining rapidly with extreme physical inactivity or more slowly with aging, while preventing inactivity can increase functional capacity (considered in specific detail in the aging section). Importantly, a direct relationship between functional capacity and survival is a cornerstone of general medicine theory. A major predictor of functional capacity is maximal aerobic capacity (VO2max), which while directly testing cardiovascular fitness and integrity also represents a combination of other physiologic components. For instance, VO2max also depends on pulmonary and muscle function, health status of other organ systems, nutritional status, medications, orthopedic limitations, and others (352). An aerobic functional capacity in patients under 4-metabolic equivalents (METs), a typical demand during normal daily activities, increases postoperative (time from admission to discharge from surgery) cardiac and long-term risks (155). In another study, patients were grouped by MET capacity in relationship to complication prevalence after they underwent angiographically verified coronary artery disease and subsequent open abdominal nonvascular surgery. (265). Those from the group < 4 METs had cardiologic complications in 64% of cases, the 4–7 METs group had 29%, and the 7–10 METs group had 8%. These remarkable findings can be extrapolated to other stresses where the probability of complications, and even survival, is dependent upon the functional capacity needed to maintain homeostasis.
2.4 Physical fitness vs. physical activity
Some people incorrectly use physical fitness and physical activity interchangeably. The CDC defines physical fitness as “The ability to carry out daily tasks with vigor and alertness, without undue fatigue, and with ample energy to enjoy leisure-time pursuits and respond to emergencies. Physical fitness includes a number of components consisting of cardiorespiratory endurance (aerobic power), skeletal muscle endurance, skeletal muscle strength, skeletal muscle power, flexibility, balance, speed of movement, reaction time, and body composition”. The CDC defines physical activity as “Any bodily movement produced by the contraction of skeletal muscle that increases energy expenditure above a basal level” (90)..
Inherited genes and their interaction with physical activity levels determine physical fitness. However, chronic physical activity levels themselves modulate fitness. Further, the levels of physical activity, themselves, modulate whether fitness improves. For example, Sisson et al. (478) concluded that the most important finding of their study was that greater volumes of exercise were associated with a lower probability of being a nonresponder. The percentage of non-responders at a given level of training progressively decreased as the exercise volume increased.
2.5 Cardiorespiratory fitness (CRF)
We define CRF as the capacity of the cardiovascular (heart and blood vessels) and respiratory (lungs) systems to supply oxygen-rich blood to the working skeletal muscles and the capacity of the muscles to use oxygen to produce energy for movement. The gold standard to determine CRF is the aforementioned VO2max, or maximum aerobic fitness. However in large clinical human studies, an acceptable surrogate for VO2max is the length of time running or cycling in standardized test, assuming appropriate physiological/biochemical/psychological proof of exhaustion is obtained (65, 263).
The majority of data about fitness and physical activity is focused on aerobic fitness. Data indicates that rapid, severe physical inactivity can rapidly decrease CRF. For instance, in the Dallas Bed Rest study, healthy, young males’ VO2max decreased 27% after 20 days of continuous bed rest (454) and another study in Denmark 2 weeks of reducing daily step number from 10,501 to 1344 VO2max decreased 7% (389).
2.6 Strength fitness
We define strength fitness as the capacity of the skeletal muscle to move an external load. Strength is highly dependent upon skeletal muscle mass, which contains a major genetic component (Discussed later in Twin studies-Modulation of twin health by physical activity), and is sensitive to decreased mechanical loading resulting in skeletal muscle atrophy regardless of endowed muscle mass (49, 508).
2.7 Balance and flexibility fitness
We define balance fitness as the ability to control the body’s position throughout movement,and flexibility fitness as the ability to achieve an extended range of motion. Both have components of genetic inheritability and are also trainable (Discussed later in Twin studies-Modulation of twin health by physical activity).
2.8 Definition of chronic diseases and their prevalence
We define chronic disease as a disease slow in its progress (decades) and long in its continuance, as opposed to acute disease, which is characterized by a swift onset and short course.
Medicine, public health, pharmaceutical industry, and educational systems have reduced infectious diseases and early life mortality resulting in record average life spans for much of the human population. In place of infectious diseases most people in the US now die of chronic diseases.
The CDC Website states, “Chronic diseases—such as heart disease, cancer, and diabetes—are the leading causes of death and disability in the United States. Chronic diseases account for 70% of all deaths in the U.S., which is 1.7 million each year (85). These diseases also cause major limitations in daily living for almost 1 out of 10 Americans or about 25 million people (85), The CDC further wrote, “Chronic diseases – such as heart disease, stroke, cancer, diabetes, and arthritis – are among the most common, costly, and preventable of all health problems in the U.S.” (86). In addition to the CDC, former US Secretary of Health and Human Services, the Honorable Michael O. Leavitt in the 2008 Physical Activity Guidelines for Americans, wrote,
Along with President Bush, I believe that physical activity should be an essential component of any comprehensive disease prevention and health promotion strategy for Americans. We know that sedentary behavior contributes to a host of chronic diseases, and regular physical activity is an important component of an overall healthy lifestyle. There is strong evidence that physically active people have better health-related physical fitness and are at lower risk of developing many disabling medical conditions than inactive people (532).
2.9 Definitions of types of prevention
For the purposes of this article, physical activity is presented as primary prevention of physical inactivity. The CDC defines physical inactivity as an actual cause of chronic conditions (213, 345). Physical activity, itself, rarely causes chronic conditions, e.g., participation in specific sports improves general health, but can increase the risk of osteoarthritis in specific populations (71); discussed later in section “Osteoarthritis”. The next definitions are taken from a commissioned paper by the U.S. Institute of Medicine (267).
Prevent implies taking advanced measures against something possible or probable. Prevention in medicine has been divided into three progressive stages – primary, secondary, and tertiary (267).
“Primary prevention refers to health promotion, which fosters wellness in general and thus reduces the likelihood of disease, disability, and premature death in a nonspecific manner, as well as specific protection against the inception of disease” (267).
“Secondary prevention refers to the detection and management of pre-symptomatic disease, and the prevention of its progression to symptomatic disease. Screening is the dominant practice…The margins between primary and secondary prevention can at times blur (268).”…For example, `”If hypertension is defined as a disease, its treatment is secondary prevention; if defined as a risk factor for coronary disease that does not yet exist, it is primary prevention” (267).
“Tertiary prevention refers to the treatment of symptomatic disease in an effort to slow its further progression to disability, or premature death…there is a legitimate focus on prevention even after disease develops, such as the prevention of early cancer from metastasizing, or the prevention of coronary disease from inducing a myocardial infarction or heart failure. This domain also encompasses rehabilitation, the purpose of which is to preserve or restore functional ability, and thus prevent its degeneration” (267).
2.11 Application of exercise to prevention categories
Examples for our view that exercise is a primary, secondary, and tertiary preventer of disease are as follows: 1) Primary prevention (direct treatment of cause to prevent disease occurrence) is voluntary avoidance of physical inactivity or treatment of physical inactivity with physical activity; 2) Secondary treatment [eliminating one cause (physical inactivity) of existing hypertension by eliminating physical inactivity] is treatment of existing hypertension with physical activity; and 3) Tertiary prevention with physical activity is cardiac rehabilitation where exercise benefits do not reverse the anatomical pathology from myocardial infarction. We propose that the greatest health benefit of physical activity is primary prevention of 35 chronic diseases/conditions to become clinically overt. This article is largely restricted to consideration of primary prevention of inactivity as an actual cause of chronic conditions.
(TO BE CONTINUED)
Frank W. Booth, Ph.D.,1 Christian K. Roberts, Ph.D.,2 and Matthew J. Laye, Ph.D.3 SOURCE https://www.ncbi.nlm.nih.gov 2012