Exercise Training and Cardiovascular Health with Aging
Mr. R started jogging in his early 30s, and typically ran 31/2 miles per day three times a week at an 11 min/mile pace. In his early 40s, he increased his distance to 5 miles per day three times weekly. Over the next decade, his exercise regimen varied but he continued to be a recreational jogger running 12-15 miles per week at a reduced pace. At age 56, he volunteered for a high-intensity exercise research study in our laboratory for the purpose of improving his running pace and health. After the 9-month training period, his maximal aerobic capacity (VO2max) increased from 38 to 46 mL/kg/min and his body mass index (BMI) decreased from 27.8 to 26.0 kg/m2. He was now running 25 miles per week at 10 min/mile pace. At 60 years of age, he was re-evaluated at longitudinal follow-up and his VO2max had decreased to 37 mL/kg/min. He reported that both his running intensity and distance were reduced to 12-15 miles per week at a pace of approximately 11-12 min/mile. At this time, he agreed to participate in another 9-month supervised training protocol, which resulted in an increase in VO2max to 40 mL/kg/min. He was re-evaluated again at age 64, at which time his training regimen consisted of running 31/2 miles per day three times weekly at a 12-13 min/mile pace, and his VO2max was measured at 35 mL/kg/min. When he was again seen at age 71, his VO2max was 33.4 mL/kg/min. At this point, he reported that he had stopped running four years previously due to concerns of falling and injuring himself but continued to walk vigorously on a treadmill at 4 mile/hr at 5% grade three times a week. Mr. R expressed an interest in retraining at a higher intensity and wondered whether he could achieve his former fitness levels. Currently, he is enrolled in a new exercise research program, and at age 71 he is not on any medications. (See Figures 1 and 2 for other metabolic variables over the 15-year period.)
Exercise Is Paramount to Good Health
Weight Loss at Any Age Improves Cardiovascular Health
Aging is accompanied by a decline in functional reserve as reflected by a gradual decrease in VO2max. In fact, the functional capacity of the cardiovascular system of adults over the age of 70 years is less than half that of young individuals, with some older individuals exhibiting VO2max values lower than that required to perform many activities of daily living. The etiology of the decline is multifactorial and attributable to decreases in muscle mass and function, sedentary lifestyle, weight gain, and the development of both subclinical and overt cardiovascular and musculoskeletal diseases, as well as biological aging.
The importance of lifestyle in cardiovascular health and fitness is substantiated in longitudinal studies that in contrast to the approximate 10-15% per decade decrease in VO2max after age 25-30 years seen in cross-sectional studies, the decline in VO2max among older individuals who remain physically active is variable and dependent on the training intensity and volume regimen that is followed over the person’s lifespan.1-4 Pollock et al3 demonstrated no significant change in VO2max among athletes (50-82 years of age) who maintained the same intensity of training over 10 years, whereas there was a 13% per-decade decline among those who decreased their training intensity and volume. Following a subset of these athletes for an additional 10 years demonstrated the difficulty in maintaining an extremely high degree of aerobic fitness with aging. A 23% per-decade decline in VO2max was observed even among those athletes who maintained a high-intensity training regimen, whereas those who had reverted to more moderate-intensity training experienced decreases of 34% per decade.4
More recent results by Katzel et al2 showed that even among athletes who maintained their training volume and intensity, VO2max declined by 5.8% per decade. Furthermore, the decline ranged from 26.5% among those who significantly reduced their training volume and intensity, to 41% among those only participating in more recreational leisure-time physical activity (LTPA). Katzel et al2 also stratified the former athletes by age to determine if the initial age affects the decline in VO2max. Aerobic capacity declined by 18% per decade for men in their 50s, compared with 28% and 38% per decade for those in their 60s and 70s, respectively. These results suggest that the wide range of declines in VO2max or cardiorespiratory fitness with aging is attributable to differences in the initial age and VO2max of the study population, differences in the ability of the older athletes to maintain a high level of training, the development of diseases, as well as primary biological aging. Despite the decrease in VO2max with aging, older men and women who increase their LTPA or continue to engage in structured exercise regimens of at least moderate intensity demonstrate greater functional capacity than their sedentary counterparts.
The clinical importance of physical inactivity and poor cardiorespiratory fitness is evidenced by their consistent association with an increased risk of developing chronic diseases such as type 2 diabetes mellitus, hyperlipidemia, hypertension, and cardiovascular diseases. However, engaging in regular exercise improves the metabolic profiles of previously sedentary individuals. Prospective diabetes prevention trials in Finland and the United States demonstrate that lifestyle behavioral changes incorporating daily exercise with dietary modification adopted over a period of 3-4 years result in a 50% reduction in the incidence of diabetes among individuals with prediabetes.5,6 Master athletes in their 60s who have continuously trained for an average of 17 years are more insulin-sensitive than a comparable group of sedentary individuals matched for age and body composition,7 and also have lower plasma triglyceride (TG) and higher high-density lipoprotein (HDL) cholesterol concentrations.8 Older individuals who engage in more moderate-intensity exercise or who report higher LTPA typically also have greater HDL levels and lower TG concentrations compared to their sedentary counterparts.9 However, recent quantitative analyses of numerous training studies suggest that higher training volume of moderate-intensity exercise (1200-2200 kcal/wk) may be necessary to beneficially alter total and low-density lipoprotein cholesterol concentrations.9 Prospective cohort studies generally demonstrate that physical activity or physical fitness is associated with a reduced risk of developing hypertension with aging.
A 10-year follow-up of middle-aged men (35-65 years) showed that the relative risk of developing hypertension was 60-70% greater in sedentary men in the lowest tertile of total daily energy expenditure and in the lowest intensity of LTPA.10 The Atherosclerosis Risk in Communities Study11 observed that white middle-aged men (45-65 years) in the highest quartile of LTPA that involved mainly cycling and brisk walking had a 34% lower risk of developing hypertension over a 6-year period. A recent Finnish prospective study showed that the protective effect of physical activity in the development of hypertension was evident in both middle-aged men and women after an 11-year follow-up period.12 A meta-analysis of clinical trials demonstrated that aerobic exercise is associated with a significant reduction in mean systolic blood pressure (BP) by 3.8 mm Hg and mean diastolic BP by 2.6 mm Hg in normal and hypertensive subjects.13 Similar reductions in both systolic and diastolic BP with exercise were reported for both normal and hypertensive men in another meta-analysis, that also revealed that aerobic training three to five times per week at an intensity of 40-50% of VO2max was as effective in reducing BP as training at greater than 70% of VO2max.14
Various studies demonstrate that a sedentary lifestyle and poor cardiorespiratory fitness are associated with abnormalities in the individual constituents of the multifaceted metabolic syndrome. However, the overarching importance of physical activity to this morbid constellation is evidenced by recent epidemiological studies demonstrating that healthy middle-aged men with low levels of LTPA and cardiorespiratory fitness are far more likely to have the metabolic syndrome.15 Participants engaging in less than 3.6 hr/wk of any LTPA were 64% more likely to have the metabolic syndrome than those participating in more than 6.8 hr/wk of physical activity. In addition, the least fit men with a VO2max of less than 29.1 mL/kg/min were almost seven times more likely to have the metabolic syndrome compared to the most fit men with a VO2max of greater than 35.5 mL/kg/min. In a large cohort of men and women enrolled in the Aerobics Center Longitudinal Study at the Cooper Clinic in Dallas, there was a strong dose–response relationship between total treadmill time (an indirect measure of cardiovascular fitness that is highly correlated to VO2max) and the number of metabolic abnormalities.16
In addition to presenting challenges to maintaining physical independence and quality of life with aging, low cardiorespiratory fitness is also an independent predictor of cardiovascular disease and all-cause mortality. During a 6-year follow-up period, peak exercise capacity was the best predictor of risk of death among older men with and without cardiovascular disease referred for treadmill exercise testing.17 The risk of death from cardiovascular events among those with an exercise capacity of less than 5 metabolic equivalents (METs) was nearly double that of those with an exercise capacity above 8 METs. Moreover, every 1 MET increase in exercise capacity was associated with a 12% improvement in survival rate. Finally, the relative risk for death from any cause increased significantly as exercise capacity decreased when subjects were grouped according to the presence of risk factors such as smoking, diabetes, obesity (BMI > 30), history of hypertension, cholesterol higher than 220 mg/dL, as well as exercise-test variables such as ST-segment depression, or development of arrhythmia.17
Retrospective analysis also demonstrates that exercise capacity had the strongest association with overall mortality and cardiac events among older men and women.18 Each 1 MET increase in peak treadmill workload was associated with an 18% reduction in cardiac events among elderly subjects.19 Results from the Baltimore Longitudinal Study of Aging demonstrate that higher LTPA and cardiovascular fitness significantly reduce the risk of coronary events in middle-aged and older men.20 Subjects in the highest tertile of high-intensity LTPA had 61% fewer coronary events than those in the lower tertile, whereas older men with a 1-standard deviation higher peak VO2max experienced a 39% lower risk for coronary events.20 The vascular endothelium plays an important role in the regulation of vascular tone and the maintenance of cardiovascular health. Endothelial dysfunction, characterized by reduced nitric oxide availability, is a common characteristic of several diseases associated with aging, such as diabetes, hypertension, and dyslipidemia.
Recent studies demonstrate an age-associated decline in endothelium-dependent vasodilation in sedentary, relatively healthy men that was not evident in older endurance-trained men.21 Moreover, three months of moderate aerobic exercise training restored vascular function in previously sedentary middle-aged and older men.21 The mechanism by which exercise protects the vascular endothelium is by preventing nitric oxide breakdown and preserving nitric oxide availability.22 In older athletes, the ability of NG-monomethyl-L-arginine (L-NMMA) to blunt the vasodilating effect of acetylcholine was similar to that in young sedentary and athletic controls. In contrast, L-NMMA failed to blunt the vasodilatory effect of acetylcholine in elderly sedentary individuals, demonstrating the presence of impaired receptor-activated nitric oxide bioavailability.22 Thus, physical activity can prevent the reduction in nitric oxide availability characteristic of impaired endothelium-dependent vasodilation that occurs with sedentary lifestyle in aging.
The local release of tissue-type plasminogen activator (t-PA) from the vascular endothelium is critical for vascular health and homeostasis. Endurance-trained older men did not demonstrate the age-related decline in the net release of t-PA that was evident in sedentary individuals of similar age.23 In addition, three months of aerobic exercise significantly increased the capacity of the vascular endothelium to release t-PA in older men.23 Thus, although endothelial t-PA release is reduced in older sedentary men, it appears that adapting a routine of continuous exercise may reverse this impairment. Participation in regular exercise programs is an effective way to reduce or prevent a number of functional and metabolic declines known to occur with advancing age.
The current recommendations of to the American College of Sports Medicine (ACSM) and the Centers for Disease Control and Prevention (CDC) are that every adult should accumulate 30 minutes or more of moderate continuous aerobic activities most days of the week that involves rhythmic movement of large muscle groups, at an intensity equivalent to 65-90% of maximum heart rate (HRmax = 220 – age) or 50-80% of heart rate reserve (HRR) (ie, HR for exercise is calculated as HRR = HRmax – HRrest x desired training intensity + HRrest).24 A structured exercise program for adults should start at a moderate intensity of approximately 65% HRmax or 50% HRR and gradually increase (preferably every 2-4 weeks) until the individual can exercise at 80-90% HRmax or 70-80% HRR. In the initial state of the exercise program, the duration of the exercise should start with short bouts of 15-20 minutes, then gradually increase by 5-10 minute intervals until an accumulated bout of 30 or more minutes at moderate intensity can be achieved. It is also important to recognize that the start and end of every exercise session should include a warm-up and cool-down of at least 5-10 minutes at a low intensity. For example, a 75-year-old person with an HRrest of 70 beats/min and an HRmax of 145 beats/min would be prescribed a training intensity of 108-135 beats/min using HRR or 94-131 beats/min using HRmax. The ACSM recommends that most adults without symptoms of coronary heart disease do not need a formal medical examination and exercise testing if moderate-intensity exercise is prescribed. However, for older individuals with heart disease or for individuals who are over 45 years of age with two or more risk factors for cardiovascular disease, most experts recommend a pre-exercise assessment including a complete medical history and physical examination and an exercise stress test in most cases.
Other organizations such as the National Institutes of Health (NIH) Consensus Development Program on Physical Activity and Cardiovascular Health concludes that intermittent or shorter bouts of moderate intensity activities such as brisk walking, cycling, or swimming of at least 10 minutes duration, with an accumulated duration of at least 30 minutes per day, also have cardiovascular health benefits. The Department of Health and Human Services (HHS) recently issued similar recommendations to accumulate at least 30 minutes of moderate-intensity physical activity per day. In addition, it recommended an increase to 60 minutes of moderate to vigorous activities per day to help maintain body weight and help prevent the gradual body weight gain with aging, and 60-90 minutes of daily moderate-intensity activity to sustain recent weight loss in adulthood. Alternative training regimens such as the 10,000 Steps Program could also be adapted to increase LTPA. Walking 10,000 steps is the approximate equivalent of walking 5 miles. This programs calls for individuals to increase their physical activity level by consciously monitoring the amount of steps they take daily. The routine starts by setting a goal to first increase step counts by an additional 2500 steps per day above daily routine. At the end of each week or two-week period, the amount of steps can be increased by 500 increments until the final goal of 10,000 daily steps is accomplished. Furthermore, although this review primarily addressed the effects of aerobic exercise on cardiovascular health, an emerging body of literature regarding the benefits of resistive exercise and improvement in strength suggests that older individuals may also consider adding a strength-training routine to prevent the loss of muscle mass and strength often seen with advancing age.
It is well recognized that the functional capacity of the cardiovascular system as assessed by maximal aerobic capacity or VO2max declines with advancing age. This decrease contributes to an increased risk of developing physiologic and metabolic abnormalities, which eventually can result in a loss of independence, increased incidence of disability and disease, and reduced quality of life in older adults. Moreover, because a low VO2max is an independent risk factor for cardiovascular and all-cause mortality, its decrease with age also contributes to premature death in middle-aged and older adults. Although chronic exercise does not prevent the age-related decrease in VO2max, it is evident that active and athletic individuals possess significantly greater aerobic capacity and reduced risk for cardiovascular and other associated diseases than sedentary individuals of similar age. Furthermore, regardless of age, the cardiovascular system remains highly adaptable to training. Hence, because of the beneficial effects of increased LTPA and cardiorespiratory fitness on metabolic risk factors, cardiovascular disease, and all-cause mortality, regular aerobic activities should be recommended to middle-aged and older individuals.
This work was supported by NIH grants R01 020116, T32 AG00219, K01 AG21457, and the Department of Veterans Affairs Baltimore Geriatric Research, Education and Clinical Center, and Medical Research Service, Baltimore, MD.