Sept. 21, 2003 -- How quickly your heart rate bounces back from intense exercise may predict future risk of dying from heart disease, according to a new study of women, half of whom die from America's top killer -- usually when they have few or no outward symptoms.
After studying some 3,000 women for 20 years, researchers say that even seemingly healthy women whose hearts take longer to slow down after exercising to the point of exhaustion are more than three times more likely to later die from heart disease.
This finding, published in this week's issue of The Journal of the American Medical Association, follows another study published three weeks ago that also suggested that heart rate recovery may be an important predictor of future heart disease death.
Men's Failing Hearts
The previous study, in the Journal of the American College of Cardiology, showed that older men whose heart rates did not slow down by at least 12 beats within the first minute after a treadmill exercise stress test were more than twice as likely to die from heart disease in the future. However, most of those 3,000 men either had existing heart disease or were considered likely candidates for it.
But in the new study, researchers found that even when free of heart disease symptoms, women face a higher future death rate when their heartbeat drops fewer than 10 beats per minute from its target heart rate zone, the intense heart-pumping levels achieved in vigorous workouts. This new study involved women as young as age 30, and none had significant heart disease risks when enrolled.
It's especially important because women are more likely than men to die from heart disease without first displaying symptoms or having risk factors.
Target heart rate is 220 minus your age. The researchers subtracted 5 from this number if the person was physically active -- since their heart rates were more likely to be lower to start with.
Treadmill Tests Predict Risk
The findings from both studies suggest that popular treadmill stress tests may be useful in predicting future risk of dying from heart disease. Currently, these tests are primarily used to diagnose heart disease, and not predict it, and are usually given to men suspected of having impaired blood flow or other risks; in women, the tests are deemed less reliable.
"In women, exercise stress tests are used less often because women tend to get more false positives," says lead researcher Samia Mora, MD, MHS, of Johns Hopkins School of Medicine. "And they're rarely done when women don't have outward symptoms of heart disease."
The stress test involves first walking and then running on a treadmill that steadily increases in speed and inclines while the doctor measures heart rate, blood pressure, and the heart's electrical currents. Based on these findings, they can determine if there is adequate blood flow to the heart during increased activity.
Do It Yourself
While a treadmill test, which costs about $600, is the most accurate way to gauge heart rate recovery, Mora tells WebMD that you can get a rough idea of your recovery level by doing a little math during and immediately following an intense workout.
"While you exercise at the highest level possible, check your heart rate by counting the beats for 15 seconds and then multiplying by four," she says. "Then, when you stop exercising completely, sit in a chair for two minutes and then count your heart rate again. Subtract the two numbers."
In her study, when the initial difference between those two numbers was 55 or more, women were less likely to die of heart disease decades later than when the difference was less than 55 beats at that two-minute measurement.
"And for every additional minute that the heart rate declined 10 beats or more, there was an additional 36% decrease in later death risk," she adds. "Of course, the greater initial difference between the target heart rate and recovery rate, and the more beats-per-minute and faster it decreased after exercise stopped, the better off they were."
These calculations can be taken during any type of sustained intense exercise. But it's crucial that they be taken while you are exercising at peak levels, not at levels done through brisk walking or during more moderate workouts.
Too Little Exercise
"The problem is that only 10%-15% of Americans exercise at the peak levels that are measured in treadmill stress tests; most people don't exercise long or hard enough to reach those levels in their regular workouts," says Dee Edington, PhD, who has studied the effects of exercise on some 2 million Americans during his career as an exercise physiologist at the University of Michigan Health Management Research Center.
"In my opinion, it's more important for people to get off the couch and not really worry about their heart rate recovery," he tells WebMD. "Even if they only get moderate exercise on most days, they will improve their cardiovascular fitness and probably reduce their risk of heart disease. When people exercise at a level that's comfortable, they're more likely to continue doing it for years, rather than the four- to eight-weeks that most Americans spend before quitting a new exercise program."
His recommendation: "Do the talk test," he tells WebMD. "You should be able to carry on a conversation while you're exercising, but with some difficulty because your breathing is labored. That means you're getting a good workout, but not so intense that you're more likely to quit."
Victor Katch, EdD, who wrote the most popular exercise physiology textbook in use today, agrees that do-it-yourself heart rate recovery calculations may not be necessary for the typical American and are best evaluated in a sophisticated treadmill stress test.
"There are a lot of factors that depend on how quickly the heart rate recovers -- your age, current fitness levels, even the weather," he tells WebMD. "Heart rate recovery will be slower if you exercise on a hot and humid day. It's really hard to give hard-and-fast rules that apply to everyone."
Still, both men say that most people should notice a distinct slowing of their heart rate after 5 minutes of stopping a good workout, and be fully recovered to their resting heartbeat within 10 to 20 minutes.