For many of us, exercise is synonymous with cardio. Want to lose weight? Get in shape? Boost your heart health? You better pound the pavement. Or cycle the calories away. Get your heart rate up, sweat it out… you know the drill.
“Cardiovascular exercise is one of the best things you can do to reduce your risk of disease and death, improve energy and well-being, and help perform activities of daily living with ease,” says exercise physiologist Kristen M. Lagally, Ph.D., professor of kinesiology at Illinois State University.
After all, cardio has long been known to reduce the risk of heart disease—the number-one cause of death in the United States. And, 2017 research published in Cell Metabolism even found that performing high-intensity cardio intervals slows aging at the cellular level. More than that, in one British Journal of Sports Medicine study, researchers even found that a twice-weekly cardio routine increased the size of the hippocampus, the region of the brain responsible for memory and learning, in women.
Heart healthy, brain-boosting, and anti-aging? Sounds great. But before you commit to cardio, cardio, cardio, know that more isn’t necessarily better.
Too Much of a Good Thing?
In a study of more than 5,000 healthy joggers and sedentary adults done by Journal of the American College of Cardiology, researchers found that jogging one to 2.4 hours per week was associated with the lowest risk of death. But as jogging times increased from there, so did the risk of death—with strenuous exercisers having a mortality rate on par with adults who didn’t exercise at all.
What gives? Like all forms of exercise, cardio stresses the body to force it to adapt and come back stronger, Lagally says. Work out too much, though, and you break it down without giving it a real chance to build itself back up.
Here are three main reasons doing too much cardio can backfire—as well as ways to get your routine on the right track.
It Sabotages Muscle-Building
In one Obesity study of 10,500 men, cardio came up short in preventing abdominal weight gain. Why? Because unlike strength training (which proved to be far more beneficial at fighting belly fat), cardio didn’t significantly increase participants’ levels of lean, metabolism-revving muscle, according to the researchers. While strength training burns calories while promoting an increase in muscle mass, cardio can actually burn calories from that muscle mass.
“When you’re young, avoiding muscle-building exercises and performing strictly cardio may not result in significantly noticeable problems,” Lagally says. But over time, it can exacerbate sarcopenia, the natural loss of muscle that occurs with age (and can start as early as 30 or 40) and limit your ability to perform everyday tasks.
What’s more, that muscle loss can also cause your basal metabolic rate—the number of calories that you burn just being alive—to decline. It’s the perfect storm for weight gain.
Related: Exactly What To Eat To Build Muscle
What To Do About It:
Keep track of your muscle mass by regularly stepping on a bathroom scale that calculates your body fat percentage, recommends San Diego bariatric surgeon Julie Ellner, M.D. The goal is to never lose muscle. If you lose weight while your body fat percentage stays the same or increases, that means you need to up your muscle-building game. No matter how much you love cardio, schedule at least two days per week of strength-focused exercise.
It Makes You Eat (Or Think You Can Eat) Everything
Research goes back and forth on whether exercise increases or decreases appetite, especially in women. But as anyone who has ever trained for a marathon can attest, if you do enough cardio, at some point you are going to wind up ravenous. Unfortunately, many cardio bunnies overestimate the number of calories they burn during their workouts, leading them to over-consume calories later—which leads to gain weight instead of loss.
What To Do About It:
Keep your eyes off of your cardio machine’s display. When researchers at the University of California at San Francisco’s Human Performance Center tested the calorie-counting accuracy of various machines, it found that the treadmill overestimated caloric burn by an average of 13 percent while the elliptical overestimated by a full 42 percent.
Instead of worrying about how many calories you cardio burns—and how many calories you should eat as a result—Ellner recommends focusing on eating according to your hunger cues. Even if your workout does rev your hunger a bit, that’s OK. Your body knows what it needs to best recover from your cardio sessions. Eat when you are slightly hungry and stop when you are slightly satisfied.
Related: 5 Myths About Your Metabolism—Busted
It Overstresses Your Body
“With cardio, adequate recovery is key,” Lagally says. “Without it, you increase your risk of overtraining syndrome, which can include regular and continued soreness, overuse injuries like stress fractures, reductions in performance in spite of continued training, a sense that their regular exercise sessions feel more difficult than normal, repeated illnesses, or changes in GI tract function.” Anything sound familiar?
What To Do About It:
Pay attention to your mood—it often shows symptoms of overtraining far earlier than your body does. If you notice that you have a persistently blue or irritable mood, or just don’t feel as into your workouts as usual, that may be your body telling you to dial things back.
Lagally recommends taking one or more days off from your typical cardio routine, cutting the intensity or duration of your sessions, or replacing one of your weekly cardio workouts with some cross-training.
“It can be difficult for those who rely on cardio, or specific modes of cardio like running, to cut back,” Lagally says. “But in the end, making changes in frequency, mode, duration, and intensity to allow for greater recovery will ultimately improve performance, caloric expenditure, and reduce the risk of overtraining issues.” So, to break out of a rut, you’ll also have to break out of your go, go, go routine.