Aging and Exercise - The Older Cardiovascular System

Aging and Exercise

Is High-Intensity Training Good for the Older Cardiovascular System?

By Jim Ragbag, PhD

Many runners, especially masters or veterans, profess to run primarily for the competition. However, many also run “for the health of it,” hoping that an offshoot of their training will be an improved medical future. This hope is especially directed at the cardiovascular system, undoubtedly because many of their non-running friends are so markedly affected by the diseases of this system which account for most of the deaths and disabilities in older Americans.

A primary goal of our previous research team in a St. Louis medical school was to assess the cardiovascular effects of the training that older athletes undergo for distance running and cycling competitions. A key variable exercise physiologists use to assess cardiovascular function is maximal oxygen consumption (VO2max). VO2max is the amount of oxygen a person can utilize when he is working maximally, usually while running at his 10K race pace up a gradually steeper hill on a treadmill.

VO2max decreases in most people by roughly one percent per year after age 25; however, most people also become much less active as they age, a factor, which will markedly affect their VO2max. Thus, it is not known how much of this age-related decrease in VO2max is really due to aging and how much is due to this tendency to become less active as we get older.

We addressed this question in older athletes because they try to keep the same high levels of physical activity as they age to maintain their race performances. When we compared the VO2max values of older runners to younger runners training the same, the older athletes still had lower VO2max values; however, the difference was only 0.5 percent per year, or about half of what was found previously. In a follow-up study, older runners who maintained the same training over a 10-year period also lost VO2max at a rate of 0.5 percent per year. Our interpretation of these results is that Mother Nature intended for our maximal exercise capacity to decrease 0.5 percent per year; however, we have added another 0.5 percent/year to this rate of decrease because we decrease our physical activity levels as we age.

Most exercise physiologists believe that VO2max is primarily limited by how much blood the heart can pump per minute – the cardiac output. Cardiac output is a function of the heart rate, the runner of heartbeats per minute, and the stroke volume (the amount of blood pumped per heartbeat). Maximal heart rate decreased with age by about one beat per year from an initial value of 220 beats/minute. This rate of decrease is unaffected by whether or not a person trains. Thus, one reason an older person’s VO2max is lower is because his heart beats slower during maximal exercise, leading to a lower maximal cardiac output and less oxygen delivery to the working muscles.

Other investigators have also reported that an older person’s heart pumps less blood per beat (a lower stroke volume) during maximal exercise; however, the stroke volumes of older athletes during maximal exercise are the same as those of younger athletes training the same. Thus when older athletes (average age of 59 years) were matched to younger runners (average age of 22 years) in terms of training mileage and type, the older athletes had lower VO2max than the younger runners.

However, the difference in VO2max between the two groups of runners was only half that expected. The key difference between these and previous results is that these athletes of different ages had the same physical activity levels; and the difference in VO2max between the two groups was due to the older athletes’ lower maximal heart rate, something that is not affected by exercise training.

We also assessed the impact of these older athletes’ training on their risk factors for heart disease. The older runners still had higher blood cholesterol levels than the younger runners training the same, and they had the same cholesterol levels as their sedentary peers who had the same low levels of body fat. The older runners only had lower blood cholesterol levels when compared to their sedentary peers who were overweight. Thus, cholesterol levels increase with age independent of physical activity levels. However, the older athletes’ training helped them to maintain a low level of body fat resulting in lower cholesterol levels.

However, in terms of their high-density lipoprotein (HDL) cholesterol, the older runners came out smelling like roses. This is the “good” cholesterol, with high levels of HDL lowering a person’s risk for heart disease. The masters athletes had very high levels of HDL cholesterol – on the average; it was 20 percent higher than even the younger runners were! Their levels were also 30 percent higher than in the much younger sedentary men and 50 percent higher than their sedentary compatriots of the same age were.

HDL cholesterol can be further divided into HDL2 and HDL3, with the HDL2 subtraction really being the “good” cholesterol. Studies underway by our research group here in the Baltimore-Washington area show that older athletes again have markedly higher levels of this “good” cholesterol than their sedentary friends of the same age. Thus, one benefit of the older athlete’s training is a blood lipid profile that substantially lowers his risk of developing heart disease.

Two other heart disease risk factors we have studied in older athletes are glucose and insulin metabolism. These are measured during an oral glucose tolerance test in which we assess how quickly glucose is cleared from the blood after drinking a 400-calorie, concentrated glucose drink and how much insulin is secreted into the blood to remove the glucose. An individual’s risk of developing heart disease increases the longer the glucose stays in the blood, the higher the glucose levels are, and the more insulin is secreted.

But older, endurance-trained athletes needn’t worry about these risk factors because their responses to oral glucose-tolerance tests were exactly the same as younger runners undergoing the same amount of training. Thus, these older men are very glucose-tolerant (they clear glucose from the blood very quickly), and very insulin-sensitive (their insulin levels increase only minimally to clear the glucose from the blood). The older sedentary men in this study and the American population, in general, become both glucose-intolerant and insulin-resistant with age, but older athletes have completely avoided this supposedly age-related deterioration in metabolic function. (Other studies we have completed show that when these older athletes stop training for short periods, they lose these training-induced benefits very quickly.)

These studies have provided substantial evidence that some of the deteriorations in cardiovascular function and heart disease risk factors commonly attributed directly to aging are probably due to decreasing physical activity levels and changes in body composition that occur with age in industrialized societies. Similar studies on older, well-trained endurance athletes are continuing in our laboratories at the University of Maryland in College Park and the University of Maryland School of Medicine in Baltimore, and we are always enrolling new athletes in these studies. The benefits for the athletes are substantial, as they receive a wealth of information about their cardiovascular and metabolic systems that, in many cases, is only available from research laboratories. These results are all made available to the participant and his or her physician. There is absolutely no charge for any of these services.

We also allow the older athlete to learn about his or her health and medical status. Currently, we are specifically enrolling well-trained male and female runners over the age of 60; however, if you do not fit into these categories but are still interested, please contact us!

If you are interested in participating in these studies now or at some time in the future, please contact the University of Maryland, College Park, MD.

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