At extremes, cardio can contribute to cardiac plaque, irregular heartbeats and heart disease.
In fact, when Duke University researchers compared the effects of various eight-month-long exercise programs on men and women’s cardiovascular health, they concluded that, minute-per-minute, moderate-intensity, steady-state cardiovascular exercise is where it’s at. Examples include running, cycling, swimming and rowing – anything that keeps your heart rate elevated and allows you to get out several words, but not quite a full sentence, at a time.
At this intensity, steady-state cardiovascular exercise improves heart health by improving HDL (good) cholesterol, blood pressure and triglyceride levels as well as insulin sensitivity, explains Dr. Dermot Phelan, director of the Cleveland Clinic’s Sports Cardiology Center. What’s more, it expands the body’s blood vessels and strengthens the heart muscle.
But research shows that too much of anything, cardio included, really is a bad thing. For instance, in a large-scale 2015 study published in the Journal of the American College of Cardiology, light and moderate joggers were less likely than non-runners to die during the study’s two-year follow-up, while strenuous joggers had the same mortality rate as sedentary folks.
Meanwhile, research shows that male marathoners have increased levels of arterial plaque, and endurance athletes have a five-fold risk of atrial fibrillation – an irregular heartbeat that can lead to blood clots, stroke, heart failure and other heart-related complications – compared with non-athletes.
So why does cardio, when taken to extremes, come with diminishing – and eventually, negative – returns? Experts believe that it all comes down to oxidative stress. The physiological damage placed on the body’s cells during exercise, oxidative stress is what spurs the body to recover, grow back stronger and, over time, become healthier. However, when stress levels become too great, the immune system can’t keep up.
“It brings up the concept of overtraining,” says Phelan, nothing that any form of exercise, when practiced in excess, can contribute to harmful levels of inflammation in the body. Cardiovascular exercise, however, is more apt to be sustained for multiple hours at a time compared to higher-intensity exercises such strength training and sprinting. Think about it: Any endurance event – whether it’s a triathlon or an ultramarathon – is a cardiovascular undertaking.
What’s the Minimal Effective Dose for Cardio?
When it comes to anything health-related, be it meds or marathons, scientists like to focus on the “minimal effective dose.” Why take five pills when one will do the job? And the extra four may cause more harm than good. The same logic can be applied to cardio.
“Cardiovascular exercise makes the greatest health difference in those who go from being sedentary to active,” Phelan says. But when does it result in peak cardiovascular health? The scientific jury is still out.
“There is no way to identify one optimal point because each person responds to cardiovascular exercise differently based on such factors as overall daily life stressors, genetics and nutritional status,” explains National Strength and Conditioning Association board member Brad Schoenfeld.
For instance, in the Journal of the American College of Cardiology study, it was those who jogged for one to just over two hours per week who had the lowest risk of dying during the study’s follow up, but the American Heart Association recommends more.
Specifically, AHA guidelines specify performing at least two-and-a-half hours of moderate-intensity exercise (steady-state cardio) per week or one-and-a-quarter hours of vigorous exercise (high-intensity interval training) per week for optimal cardiovascular health. That’s in addition to at least two strength-training workouts per week. (Strength training doesn’t directly improve cardiovascular health in a significant way, but by decreasing body fat levels and improving muscular health, it can in turn reduce cardiovascular risk factors.)
“Research suggests that people can perform up to nine hours of moderate exercise or five hours of vigorous exercise per week and still see some cardiovascular benefits,” Phelan says. “After that, the data becomes a little murky.”
Chances are, though, you’ve still got a ways to go before your cardio routine stops benefiting your heart. After all, when a team of international researchers weighed the pros and cons of cardio evidence in the Journal of the American College of Cardiology, they noted that only half of adults meet – let alone exceed – the American Heart Association’s current minimum exercise recommendations.
To get the maximum benefit from your cardio routine, Schoenfeld recommends considering your current health, exercise experience, family health history and stress levels. “Whether you are in youth sports, an adult or senior athlete, start by getting proper assessment by your health care professional as well as an accredited and certified trainer,” he says.
Until then, just keep moving.
First appeared on USNews.com