Exercise and Chronic Disease
Karl B. Fields
Kenneth P. Barnes
Catherine R. Rainbow
Medical problems lead to approximately 70% of the visits that athletes make to doctors.
Many athletes, particularly those older than age 35, have chronic medical problems.
In recent decades, obesity, diabetes, hypertension, and asthma have increased in frequency in youth and adolescents.
This chapter provides an overview of principles of healthy exercise in athletic individuals who have some of the more common chronic diseases.
According to data from the National Health and Nutrition Examination Survey (NHANES) obtained in 2007-2008, approximately 32.2% of men and 35.5% of women in the United States are obese. Overall, 68.0% of Americans are either overweight or obese (body mass index [BMI] > 25.0) (34)
In 2007-2008, an estimated 16.9% of children and adolescents between ages 2 and 19 were obese — an increase from 5.0% in 1971-1974 and 10.0% from 1988-1994 data (85). (NHANES data)
Obesity contributes to excess morbidity and mortality from hypertension, Type 2 diabetes, coronary artery diseases, stroke, gallbladder disease, sleep apnea, and osteoarthritis. Cancers with an increased frequency in obese individuals include endometrial, breast, prostate, and colon cancers (82,91).
Centripetal obesity in which the waist-to-hip ratio is high indicates a subset of individuals at much higher risk of cardiovascular diseases (91). Generally a waist circumference of > 35 inches in women and > 40 inches in men is considered high risk (82).
Some over weight athletes have achieved high levels of sports success. In sports, including football, weight throws in track and field, heavyweight wrestling, and power lifting, excessive weight has generally been considered advantageous.
Athletes often pursue strategies that lead to dietary excess and pose health risks when they are trying to gain excessive weight. These may include diets with excessive high fat and high glycemic foods.
Obesity has direct consequences in sport, for example, a much greater risk of heat illness during competition (50).
The odds of sustaining a musculoskeletal injury increase with BMI. Overweight individuals are 15% more likely and those with Class III Obesity (BMI > 40) are 48% more likely to have an exercise-related injury (33).
Highly competitive athletes may need to consume 1,500-2,000 excess calories daily during intense training. Dietary calorie consumption appears to be a learned behavior and appetite often does not decline with a reduction in activity levels in the off-season or after retirement (56). This can quickly lead to obesity.
All forms of muscular activity burn calories, but aerobic activity generally serves as the backbone of a weight-loss program. Individuals on a strength-training program or on a mixed exercise program may show comparable weight loss with a well-designed, vigorous program.
Most weight loss occurs with decreased caloric intake, but sustained physical activity is important in maintenance of weight loss (82).
A combination of a reduced calorie diet and increased physical activity has strong evidence as an effective way to achieve weight loss (80) (based on meta-analysis of 15 randomized controlled trials [RCTs])
Nonathletes have trouble losing weight on an exercise program alone perhaps because effective weight loss through exercise requires a consistent moderate-to-high level of activity.
Epidemiologists note that we have seen a dramatic gain in weight of Americans in the last 2 decades; a period with a modest increase in calorie consumption but a dramatic decline in physical activity.
As of 2007, 23.6 million Americans had diabetes with an approximate 5.7 million of those undiagnosed (22).
Diabetes mellitus is considered a cardiac equivalent because of the strong association of this disease with cardiovascular
problems. Maintaining a good fitness level lowers the risk of cardiac death and is associated with longevity (11).
In a large group of diabetics, walking at least 2 hours a week lowered cardiovascular mortality rates. This level of walking prevented 1 death per year for every 61 patients (41). A similar study demonstrated patients who performed moderate-to-vigorous exercise had a 40% lower risk of cardiovascular disease than those who did not exercise (47).
Aerobic exercise mildly lowers systolic and diastolic blood pressure (119). Aerobic exercise may also delay or prevent the development of hypertension. Good control of blood pressure (BP) lessens the risk of complications in diabetic patients.
Aerobic exercise improves lipid profiles. In a meta-analysis of > 4 weeks aerobic exercise, high-density lipoprotein (HDL) was shown to increase 9% and triglycerides to decrease by 11% — other effects were not statistically significant (54). A focused meta-analysis in diabetics (220 patients) revealed a statistically significant reduction of 5% in LDL with more than 8 weeks of aerobic exercise (53).
Diabetics are encouraged to perform 30-60 minutes of moderate-intensity exercise most days of the week.
Improved Metabolic Control
A meta-analysis of 14 studies (12 aerobic and 2 resistance) demonstrated exercise leads to a statistically significant reduction in hemoglobin A1c levels (13).
Another meta-analysis showed all types of exercise lead to statistically significant reductions in hemoglobin A1c levels (109).
Exercise improves insulin sensitivity in liver, muscle, and fat cells (117).
A single exercise session has been shown to increase insulin sensitivity for 16 hours (59).
Reduced Morbidity and Mortality
An epidemiologic study following male with Type 1 diabetics for 20 years shows those who participated in high school or college sports had lower mortality and lower incidence of macrovascular disease than sedentary counterparts (63).
Exercise has a positive effect on the self-esteem of diabetic patients and allows many to cope better with physical and emotional stress.
Scientific Consensus on Exercise Activity for Type 2 Diabetes
The American College of Sports Medicine® (ACSM) and the American Diabetes Association have concurred that physical activity has major benefits for individuals with Type 2 diabetes.
Physical activity coupled with diet helps lessen risk of developing Type 2 diabetes in obese individuals by as much as 58%.
Physical activity now has strong evidence for benefits of management in almost all target areas that complicate diabetic care (23).
The National High Blood Pressure Education Program recommends the evaluation of BP using percentiles based on age, height, and gender for children and adolescents (81).
Prehypertensive values are systolic or diastolic pressures between the ninetieth and ninety-fifth percentiles or if BP exceeds 120 mm Hg systolic or 80 mm Hg diastolic.
BP above the ninety-fifth percentile for age-adjusted norms is considered hypertension (79). BPs above the ninety-ninth percentile of age-adjusted norms are considered severe hypertension.
For adults, any levels above 140 systolic or 90 diastolic indicate hypertension.
BP is a product of cardiac output multiplied by peripheral resistance. Peripheral resistance must fall dramatically during exercise or else BP rises excessively since increasing physical activity requires a higher cardiac output than rest.
In patients whose BP rises too dramatically during dynamic exercise, the relative risk of subsequent hypertension is higher (112,120).
Heavy-resistance exercise particularly weight lifting can cause dramatic rises in BP that are transient (66).
A meta-analysis of 54 clinical trials of aerobic exercise showed reductions of systolic and diastolic BP in both hypertensive and normotensive individuals (119).
The Osaka Health Survey demonstrated that a daily walk of 20 minutes or more reduced the risk of hypertension in men. In fact, for every 26 men who walked, 1 case of hypertension was prevented (42). Vigorous exercise for as little as 30 minutes, just once weekly, also reduced risk.
Endurance exercise lowers BPs of hypertensives by 5-7 mm Hg after an exercise session or following a period of exercise training (92). BP can remain reduced for up to 22 hours following a bout of endurance exercise. The greatest decreases occur in those with severe hypertension.
The ACSM recommends performance of low-to-moderate exercise (e.g., walking), at 40%-59% of oxygen reuptake reserve (VO2R), 4-7 days per week, for a total of at least 30 minutes daily (92).
Most resistance exercise seems to benefit hypertensive athletes, although maximal resistance efforts pose theoretical
risks. Resistance exercise can supplement endurance activities (92).
The ACSM recommends that resistance training in hypertensive patients be mixed with aerobic activity (92).
CORONARY ARTERY DISEASE
Patients with known coronary artery disease (CAD) can reduce their risk of coronary events by maintaining high fitness levels (76).
Moderate exercise is recommended for individuals with CAD, and the individual’s exercise capacity should be measured by exercise tolerance testing.
Formal cardiac rehabilitation programs help coronary artery disease patients get started on a therapeutic exercise regimen.
Patients with CAD who develop the fitness to achieve a 10.7 metabolic equivalent (MET) level workload have a normal age adjusted mortality rate (76).
Recent research suggests that exercise lowers C-reactive protein (CRP) levels. Athletes, such as swimmers and runners, have significantly lower CRP levels than the average individual and the more intensely they train, the greater the decline in their CRP level. Speculation centers as to whether this may be one of the mechanisms by which exercise lowers the risk of cardiovascular disease (122).
The American Heart Association and the American College of Cardiology recommend 30 minutes of moderate intensity aerobic exercise per day, 5-7 days per week (107). Resistance training can supplement these exercises 2 days per week.
High-risk patients (e.g., those with recent acute coronary syndrome or revascularization or heart failure) should be medically supervised during exercise (107).
EXERCISE POSTCEREBRAL VASCULAR ACCIDENT
Exercise is important in primary and secondary prevention of cardiovascular and stroke risk. A study of over 16,000 men found an inverse relationship between cardiovascular fitness and stroke mortality (65).
Poststroke patients often suffer from weakness, paralysis, sensory loss, and decrease overall exercise capacity. A study by Mackay-Lyons revealed in less than 1 month after stroke, patients developed a significant compromise in exercise capacity (67).
Poststroke patients who increase activities of daily living (ADL), showed a significant increase in peak oxygen intake (39). Additionally, poststroke patients’ training on treadmills showed significant improvements of VO2max, gait and overall functional mobility, balance, and muscular activity (64,68). A supervised exercise program for stroke survivors with multiple comorbidities is effective at improving fitness while potentially decreasing risk of further disease and disability (100).
Strength training can safely be used in most poststroke rehabilitation to improve muscle strength and overall balance (100). Caution should be used in patients with uncontrolled hypertension, as well as avoidance of excessive weight and Valsalva.
The oxygen cost of exercise in hemiplegic patients is up to 2 times that of controls. This can lead to inactivity and secondary deconditioning, atrophy, osteoporosis, and impaired leg circulation (87,118).
Role for exercise during immediate poststroke period is limited by increased risk of recurrent stroke and secondary cardiac complications.
Exercise becomes increasingly important beyond the first several months to increase aerobic capacity and sensorimotor function (43,68,96,106).
Aerobic conditioning can enhance glucose regulation, mobilization of fat stores, BP, CRP, triacylglycerol (TG), total cholesterol (TC), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) (36).
There is inconclusive data relating exercise to prevention of secondary strokes.
Role and timing of exercise stress testing poststroke is controversial.
RCT of 88 men with CAD and disability (two-thirds were stroke victims) who completed a 6-month home exercise training program showed significant increases in peak left ventricular ejection fraction and HDL cholesterol and decreases in resting heart rate and total serum cholesterol.
Six months of treadmill aerobic exercise allowed patients to perform ADL at submaximal energy expenditure (68).
RCT of 42 hemiparetic stroke survivors demonstrated that they could increase their fitness by a magnitude similar to that of healthy controls in similar programs. Aerobic training 3 times weekly for 10 weeks improved peak oxygen consumption, workload, submaximal blood pressure response, exercise time, and sensorimotor function.
Fewer than 50% of patients reliably have their risk factors assessed, treated, or controlled (24).
Aerobic exercise can help improve risk factors.
Recommended exercise strategies involve large muscle activities, such as walking, treadmill, stationary cycle, arm-leg ergometry, arm ergometry, seated stepper for 20-60 minutes sessions, 3-7 days per week at 40%-70% peak oxygen uptake/heart rate reserve, or 50%-80% of maximum heart rate or rating of perceive exertion of 11-14 (40).
Flexibility stretches 2-3 days per week can help prevent contractures and improve range of motion.
Coordination and balance activities 2-3 days weekly can improve safety during performance of ADL.
RENAL DISEASE IN ATHLETES
Kidney Problems Associated With Exercise
Dehydration, hyperpyrexia, hyperkalemia, and rhabdomyolysis may all occur as a result of exercise and may lead to renal damage (32).
Rhabdomyolysis, especially in untrained athletes, can lead to renal ischemia and nephrotoxins (86).
Subsets of athletes, such as those with sickle cell trait, may have higher risk for rhabdomyolysis and renal failure.
Cardiovascular disease accounts for most deaths in patients with end stage renal disease (ESRD) (115).
[V with dot above]O2 peak (peak oxygen uptake) has been purported to strongly predict survival in ESRD patients (105). Patients with CKD (chronic kidney disease) have significantly reduced [V with dot above]O2 peaks in comparison to age and gender matched controls. Moderate exercise (< 60% [V with dot above]O2 peak) for 10-20 minutes can produce modest improvements, although CKD patients do not reach predicted [V with dot above]O2 peak.
CKD negatively affects skeletal muscle function, including atrophy, derangement, and abnormal mitochondria (39).
Resistance training can increase muscle size and strength on a low-protein diet (20).
Combined cardiovascular and resistance training helps improve cardiovascular function, strength, endurance, and muscle size. This exercise regimen produced greater increases in [V with dot above]O2 peak likely via effects of resistance training on skeletal muscle function, which thereby improved [V with dot above]O2 peak (10).
Contraindications to exercise in CKD include systolic BP > 200 mm Hg, diastolic pressure over 110 mm Hg, electrolyte abnormalities, recent myocardial infarction, or recent change in the electrocardiogram (10).
Prevention of Renal Disease
Adequate hydration is important in minimizing muscle damage, promoting myoglobin elimination, and maintaining renal blood flow.
Athletes reduce the risk of rhabdomyolysis and secondary renal failure through adequate fluid intake, avoidance of excessive heat stress, not exercising at the time of febrile illness, appropriate carbohydrate intake to avoid glycogen depletion, and exercising within the limits of their muscular tolerance.
THYROID DISEASE IN ATHLETES
Hypothyroidism and subclinical hypothyroidism are associated with decreased exercise tolerance (19,70).
Patients often develop muscle weakness, cramps, and fatigue, which is worse in elderly patients (52).
This exercise intolerance is due to increased systemic vascular resistance, which decreases blood flow to exercising muscles leading to reduced oxygen delivery and bloodborne substrate availability (52).
Replacement of thyroxin is the mainstay of treatment.
Exercise is safe when adequate replacement is maintained.
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