2017 Exercise is Medicine Conference

Aging is associated with the replacement of muscle by fat.

Waist circumference increases due to an increase in visceral fat, which causes chronic inflammation. Muscle loses quality and strength, contributing to the disabilities of old age.¹

Aging is also associated with increased insulin resistance and diabetes.

Physical inactivity accounts for many of these problems, which can be greatly reduced by exercise.

Exercise reduces blood glucose levels.

This report is based on the Exercise is Medicine conference held in Denver, Colorado, in June 2017. It reveals new findings on the favorable effects of even moderate increases in physical activity.

Fitness and Risk of Death

Robert Ross, Ph.D. (professor, Queen's University, Ontario, Canada) studies the health benefits of fitness.

People who are fit have a lower risk of death—even if they smoke and have elevated cholesterol and blood pressure—compared to unfit people that have none of those risk factors.²

Patients with dyslipidemia (elevated blood cholesterol and triglycerides) who are highly fit but are not taking statins have a substantially lower risk of dying than dyslipidemia patients taking statins who are unfit.³

Dr. Ross was chair of a 2016 American Heart Association Committee that issued a report showing that low cardiorespiratory fitness is a stronger predictor of death than smoking, high cholesterol, type II diabetes, or high blood pressure.⁴

Inactivity and Blood Vessel Health

Jaume Padilla, Ph.D. (assistant professor, University of Missouri) is concerned with the effects of physical activity on endothelial function.

Endothelial dysfunction refers to the reduced capacity of blood vessel walls (the endothelium) to dilate and thereby increase blood flow. Endothelial dysfunction is one of the early changes contributing to atherosclerosis,⁵ a narrowing of the arteries that increases the risk of heart attack and stroke.⁶ A 1% increase in endothelial function is associated with a 13% reduced risk of cardiovascular disease.⁷

Exercise prevents the decline of endothelial function that occurs with age.⁷

In one experiment, Dr. Padilla showed that only five days of reduced activity (from 10,000 steps per day to 5,000 steps per day) substantially reduced endothelial function in leg arteries.⁸

He also showed that engaging in exercise prior to prolonged sitting could prevent the endothelial dysfunction normally caused by sitting.⁹ Even fidgeting the legs for one minute out of every five can prevent the endothelial dysfunction caused by sitting.¹⁰

Finally, Dr. Padilla has also demonstrated that the endothelial dysfunction of leg arteries resulting from six hours of continuous sitting could be reversed by a 10-minute walk.¹¹

Exercise Against Aging

Brian Irving, Ph.D. (assistant professor, Louisiana State University) has an interest in the benefits of different types of exercise for the elderly. For example, resistance training, but not endurance training, has been shown to increase muscle size and mitochondrial density in the elderly.¹² Endurance training does, however, prevent mitochondria from becoming dysfunctional.¹³

Dr. Irving's team has shown that a combination of endurance and resistance exercise is the best way to improve cardiorespiratory fitness, muscle strength, and mitochondrial capacity.¹⁴

The team also demonstrated that the increase in insulin resistance that happens with aging is due to increasing fat rather than simply being an inevitable consequence of aging.¹⁵ Endurance exercise has been shown to increase insulin sensitivity.¹⁶

Exercise Capacity and Heart Health

Jonathan Myers, Ph.D. (health research scientist, Veteran Affairs Health Care System, Palo Alto, California) has established that exercise capacity is a better predictor of the risk of death than smoking, diabetes, high blood pressure, or other exercise test results.¹⁷

Exercise capacity is the maximum metabolic equivalent (MET) measured on exercise equipment. MET is the ratio of energy expended during an activity compared to the energy expended when a person is passive (such as watching television). Leisurely walking uses just over 2 METs of energy, whereas jogging uses about 7 METs.

Dr. Myers has also established that cardiorespiratory fitness (peak oxygen uptake during maximum exercise) is the best way to determine the exercise intolerance seen in heart failure patients.¹⁸

Exercise testing requires equipment and trained staff that are often not available in medical facilities. So Dr. Myers has been evaluating questionnaires that estimate exercise capacity in order to attempt to predict mortality.¹⁹

The single question, "How do you rate your cardiorespiratory fitness compared to your peers?" has proven to be very effective. Those who rated themselves lower than their peers have a 91% greater chance of dying of cardiovascular disease compared to those who rate themselves higher than their peers.²⁰

High Intensity Interval Training

Martin Gibala, Ph.D. (professor, McMaster University, Ontario, Canada) studies the effects of high-intensity interval training (HIIT). HIIT exercise involves alternating between a brief period of "all-out" effort for several seconds, and a period of resting recovery time.

Dr. Gibala conducted a study in which he compared 45 minutes of moderate intensity cycling with a HIIT protocol consisting of three 20-second "all-out" cycling efforts interspersed with 2 minutes of low-effort cycling. The two groups of previously inactive men exercised three times per week for 12 weeks.

The study showed that improvement in insulin sensitivity, cardiorespiratory fitness, and muscle mitochondrial content was the same for both groups, despite the fact that the moderate intensity cycling group spent five times more total time exercising than the HIIT group.²¹

A review of the literature showed that when overweight/obese people practiced HIIT for more than 12 weeks, they experienced a reduction in body fat, waist circumference, and blood pressure, and an increase in cardiorespiratory fitness.²²

Dr. Gibala has established that HIIT can be achieved by stair-climbing as effectively as on an exercise bike.²³

Benefits and Risks of Exercise

Barry Franklin, Ph.D. (professor, Wayne State University, Detroit, Michigan) is concerned with whether excessive exercise can be harmful.

Exercise reduces cardiovascular disease by improving the function of the heart²⁴ and blood vessels.²⁵ But excessive and vigorous exertion in those who have a poor cardiorespiratory condition and who are at increased risk of heart disease due to coronary artery disease or structural defects of the heart, has been shown to markedly increase the risk of sudden cardiac death and heart attack. Snow-shoveling is one confirmed cause of this, but any bout of excessive exercise in unfit, at-risk individuals can have this result.^26,27

Even in individuals without known heart disease, vigorous physical activity can increase the risk of acute heart attack and sudden cardiac death (SCD). This is because of the temporary stress placed on the heart by excessive exercise, making silent cardiac disease suddenly deadly when sedentary individuals overexert themselves.

This underlines the importance of beginning any program of physical activity gradually, with expert guidance, and only after a thorough evaluation of cardiovascular health and risk.

Exercise for Diabetes

Steven Malin, Ph.D. (assistant professor, University of Virginia) studies differences in insulin sensitivity, fat disposal, and the effects of exercise between individuals. He has been particularly interested in the ability of the pancreas to compensate for insulin resistance.

In the early stages of insulin resistance, blood glucose levels do not change because the pancreas can increase insulin production to compensate for the fact that insulin resistance increases the difficulty of getting glucose into cells. But eventually the pancreas becomes unable to compensate, which results in higher blood glucose and lower levels of insulin.²⁸

Dr. Malin highlights the importance of cardiorespiratory fitness for glycemic control and its importance in the production of insulin by the pancreas.²⁹

Exercise for Cognitive Function and Depression

Ryan Olson, Ph.D. (assistant professor, University of North Texas) is concerned with exercise, depression, and cognitive function.

More than 15% of the U.S. population will experience major depressive disorder at some point in their lifetime.³⁰ Dr. Olson's research suggests that depressed people ruminate about negative past experiences, and that the rumination contributes to cognitive impairment.³⁰

In an eight-week experiment in which depressed individuals did either stretching or endurance exercise, Dr. Olson found that endurance exercise reduced depressive symptoms by 58%, whereas stretching only reduced the symptoms by 22%.³¹ Endurance exercise also resulted in greater improvement in cognitive function.³¹

A 12-week study of depressed individuals compared the exercise equivalent of walking three miles per hour for 75 minutes per week with walking four miles per hour for 210 minutes per week. The greater amount of exercise resulted in greater improvement of cognitive function.³²

Christiane Wrann, Ph.D. (assistant professor of Medicine, Harvard Medical School) is interested in how exercise improves cognitive function. Exercise results in the creation of new brain cells in the area of the brain concerned with the formation of new memories.³³

A study of healthy elderly people showed that those who did endurance exercise for six months experienced increased brain volume in the prefrontal and temporal cortex, the brain areas that normally show the greatest age-related deterioration.³⁴

Dr. Wrann has been most interested in a protein called irisin that is secreted from muscle during exercise.³⁵ She has found that irisin release is caused by another exercise-induced protein, PGC-1 alpha, which is a primary stimulator of mitochondrial biogenesis.³⁶ Irisin reduces insulin resistance and obesity, and PGC-1 alpha has been shown to prolong lifespan in mice.³⁷

Exercise in Pregnancy

Michelle Motolla, Ph.D. (professor, Western University, Ontario, Canada) studies the effects of exercise on pregnant women. Dr. Mottola has shown that pregnant women who do not exercise are 2.5 times more likely to give birth to an overweight infant, and three times more likely to develop high blood pressure.³⁸

Every 2.2 pounds above average birthweight is associated with a 12% higher risk of dying from cardiovascular disease when the child becomes an adult.³⁹ Women who exercise while pregnant reduce the risk of having an overweight newborn.⁴⁰

Nearly half of the women who develop diabetes during pregnancy (called gestational diabetes) will have an overweight infant. These infants are likely to become an obese, diabetic adult.⁴¹ Dr. Mottola has conducted a clinical trial showing that exercise during pregnancy reduced the incidence of gestational diabetes and prevented excessive weight retention in the mothers after they gave birth.⁴²

Concluding Remarks

Exercise can do much to reduce the disabilities of aging, prevent diabetes, and reduce the risk of dying from cardiovascular disease.

Physicians often find it easier to prescribe a pill rather than to prescribe exercise, despite the fact that exercise may be more effective. Patients also often find that it is more convenient to take a pill than to exercise.

Exercise is a medicine without the side effects of a drug. Too many people avoid experiencing the benefits of exercise at too great a cost.

References

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