While few would argue against the benefits of exercise, including its positive impact of lowering the risk of many chronic disease states such as cardiovascular disease, there is growing concern that some endurance athletes – those performing far beyond the recommended amount of 150 minutes per week of moderate to vigorous exercise over many years - may be at greater risk for certain cardiac problems.
For example, atrial fibrillation (a-fib), the most common arrhythmia in aging adults, is seen about two to five times more frequently in aging recreational endurance athletes compared to equally healthy, non-athletes, according to Professor Emeritus Jack Goodman from the University of Toronto Faculty of Kinesiology and Physical Education (KPE).
“However, these findings are based on retrospective data obtained by asking athletes what their exercise history has been for many years,” says Goodman, who recently co-authored a study about the reliability of subjective estimates of exercise intensity among recreational athletes with Jennifer Lewis, a recent graduate from the KPE master of science program, Robert Bentley, an assistant professor at KPE, and Professors Kim Connelly and Paul Dorian from the U of T Temerty Faculty of Medicine.
“While many have shown a positive relationship between high-volumes of cumulative exercise and conditions like a-fib, the weakest link of this approach has been the estimation of exercise intensity, which is the most important component because it tells us how high one’s exercise metabolism or heart rate gets,” says Goodman. “Our concern with many of these studies is that either no measure of exercise intensity was made or, if there was, the estimations may not be accurate.”
To explore this issue further, the researchers asked 40 athletes between the ages of 41 and 69 to perform a single, one and a half to two-hour exercise training bout (cycling a 42 km course) at their own pace. Using voice-activated phone communication, they asked the athletes about their perceived intensity of exercise throughout the ride, while simultaneously measuring objective metrics of intensity, including cycling workrate, which measures how much stress is put on the heart muscle during exercise, and heart rate using specialized bike pedals and wearable technology.
The study, recently published in the Canadian Journal of Cardiology, showed that estimates of exercise intensity by middle-aged athletes can be inaccurate and quite inconsistent compared to the objective measures.
“The objective measures did not align well with their reported perceived exertion and were very inconsistent across participants during exercise, becoming more variable as the intensity of effort increased,” says Goodman. “After only 30 minutes following the completion of exercise, their ability to match their perception of intensity to the actual exercise intensity throughout the exercise session was consistently inconsistent(!)”
The study showed that the impact of endurance exercise on the body’s health is best determined by measuring both the metabolic demands of exercise and the heart rate, because these measures may be affected quite differently depending on the athlete’s level of fitness.
“We believe that many research papers examining the relationship between excessive exercise and heart health rely on overly simplistic accounts of exercise history, like cumulative hours, with no measure of exercise intensity or, if they report intensity, they have relied on estimates from questionnaires, which we have shown are not very accurate,” says Goodman.
The researchers recommend that future studies about the relationship between exercise intensity and cardiac health should measure heart rate directly, and that caution is warranted when interpreting studies that do not report any direct and objective measure of exercise intensity, or those where it has been estimated from questionnaires that may have unknown reliability.