Spend enough time on TikTok or Instagram and you’ll find someone telling you to stop jogging, step away from the stationary bike or swap your weekend trail runs for a lower-impact activity. The argument usually goes something like this: Steady cardio spikes your cortisol, inhibits muscle growth, makes you too hungry and might even contribute to faster aging. Depending on the social media platform or influencer, the advice might be to lift heavy instead, try Pilates or just take a nice slow walk—whatever will keep your heart rate low.
If you love to run, hike or cycle, this can be an unsettling message. But does it hold up? And if some cardio is fine, how much is too much?
We talked to two experts—Tamanna Singh, MD, FACC, a sports cardiologist and director of the Sports Cardiology Center at Cleveland Clinic, and Kylee Van Horn, a trail runner, podcaster and endurance sports dietitian based in Carbondale, Colorado—about what’s driving the trend, what cortisol actually does and why the healthiest approach to exercise usually sits somewhere between the extremes commonly found online.
Where the anti-cardio trend comes from
Van Horn is all too familiar with the anti-cardio messaging many of us have stumbled upon, and she most often sees it aimed at people experiencing signs of aging. “There is an idea that steady-state cardio spikes cortisol, burns muscle and ‘ages’ you faster than it helps you,” she says. “It is usually presented as ‘lift heavy’ and avoid intense cardio.”
There’s a kernel of truth to this suggestion. Strength training becomes more important as we age, particularly for people going through perimenopause or menopause. Van Horn notes that there is research showing a connection between the estrogen decline experienced during these phases and muscle and bone loss. “This gave strength training a boost that shifted the message from ‘strength training will make you bulky’ to one that was about preserving muscle mass,” she says. Singh has seen this shift in her clinic, where she says her patients are more likely to be strength training than they were even five years ago.
The trouble, Van Horn explains, is what happened next. The findings of these studies have “gotten twisted,” according to Van Horn, who says that a small body of research “has been extrapolated and blown up out of proportion.”
What cortisol actually does
It’s almost impossible to spend time online as a fitness enthusiast and not come across the word “cortisol.” And if you don’t know what it does, it’s easy to assume it’s nothing but bad news. But cortisol is just the stress hormone. While it’s true that it rises when you exercise, what that means for your health takes more nuance.
When you exercise, cortisol increases because exercise stresses the body. How high your cortisol rises depends on how long and hard you train, but it should return to baseline one or two hours after you finish. Even more importantly, the cortisol increases you get from exercise can have long-term health benefits. As Signh explains, “this stressor leads to positive adaptation over time, which includes reduction in baseline cortisol levels.” In other words, engaging in cardio exercise makes your body more resilient to all types of stress.
Van Horn puts it more bluntly. According to her, a cortisol “spike” is “normal.” What’s not normal, and what Van Horn says doesn’t get talked about enough, is chronic stress that dysregulates the hypothalamic-pituitary-adrenal (HPA) axis, your body’s central stress-response system. That usually stems from “training too much or too hard without proper fueling and recovery.” If you’ve ever embarked on a cardio training plan for running, hiking or biking without having a clear sense of how allostatic load—the accumulation of wear and tear on organs and tissues—works, what your heart rate zones are, how much fuel you need or how to build in enough time for rest or recovery, you may have experienced a version of this. But that’s not a reason to avoid cardio exercise entirely.
Singh says it’s all about balance: Cortisol bumps from exercise aren’t harmful when training is balanced with recovery. But overtraining, where load and recovery are out of whack, becomes “a big stressor in a negative way,” increasing the risk of injury and more.
It’s not the cortisol blip from a run that does damage. It’s a pattern of piling on stress without enough rest and food—and cardio exercise is only one way you can incur that type of damage. Lifting, work and even enjoyable life events like planning a big party can all add to the total. But that’s not a reason to skip out on any of those activities, either.
What cardio does for your body
Singh names a number of benefits that are specific to cardio exercise. It can improve blood pressure, cholesterol and blood sugar control, and it reduces cardiovascular risk. When it comes to the arguments that cardio will cause weight gain, Singh is, frankly, perplexed. “I’m not sure where that concern comes from,” she says. She believes cardio exercise can help reduce body fat and improve metabolism.
More importantly, Singh cautions that the number you see on the scale is rarely a perfect indicator of health. For those engaging in weight training and cardio, Singh points out that their weight may increase simply due to added muscle mass. But, it can also be influenced by a number of other variables, such as diet, hydration and electrolytes. In fact, she points out that some people’s weight can swing 4 to 5 pounds in a single day just from fluid shifts. “The more valuable metric is body composition,” she says.
So, do you have to choose between ditching cardio entirely and making it the centerpiece of your exercise routine? According to Singh, “cardio and weight training are complementary to one another.” Cardio builds aerobic efficiency, while strength training builds the muscle and tendon capacity to generate power, protect against injury, and respond better to cardio training. Both reduce cardiovascular risk.
Her advice is simple: “Bodies want to move and tend to get stiff, inflexible, and weak when they don’t.” Aerobic and strength training together help build “a resilient body and mindset.”
Hunger is a signal, not a problem
“How did we get to the point that hunger is a bad thing?” Van Horn asks. She says posts frequently frame cardio as risky because it makes you hungry, and she thinks the idea ties into broader cultural fears about weight gain. She notes that GLP-1 medications have added another layer: With a pharmacological appetite suppressant available, “there is a fear around doing too much cardio that could increase appetite because hunger is ‘bad.’”
There’s a physiological nuance here, too. Cortisol can briefly suppress ghrelin, a hunger hormone, so your appetite may dip right after hard exercise. “Hunger will typically return later and if someone hasn’t fueled enough, it might come in raging a bit,” Van Horn says. That’s your body doing its job—but it can feel confusing when you’re first adjusting to it. And it can take some time to figure out how to best fuel after exercise when you don’t always feel like it, so you’re not falling into a pit of fatigue and extreme hunger hours later when your appetite finally returns. That practice requires embracing the fact that our bodies need food to fuel the activities we want to do, rather than treating a momentary loss of appetite as a victory.
Van Horn emphasizes that hunger is “a physiological signal, not a ‘problem to avoid.’” Diet culture, however, has taught people to ignore hunger or suppress it with medication. Over time, that can erode trust in your own body’s cues, a pattern eating disorder specialists refer to as interoceptive avoidance. “In the broader cultural context, ‘I’m just never hungry anymore’ has become a status marker,” Van Horn says, which “normalizes appetite suppression as a goal in itself”—a message that’s especially risky for people already vulnerable to eating disorders.
The same logic applies to how people fuel for different exercise routines. Online, it sometimes seems like each type of training plan comes with its own trendy diet—whether that’s “clean eating” for Pilates, carb-loading for running or a paleo diet for lifting. And while the details of macronutrient ratios might shift a bit between lifting and endurance training, Van Horn says that “no matter what you are doing, you still need to have carbohydrates, protein and fats in your diet to physiologically function well.” Fueling matters, regardless of the type of exercise you’re engaging in, and it’s important to find balance with what you eat.
Figuring out what you need
So, how should you decide how much cardio to do? Start with your goals and be honest about what’s driving your choices. If you’re training for an event, your needs will look different from those of someone who just wants to stay healthy and strong.
Singh points to the American Heart Association‘s baseline: At least 150 minutes of moderate-intensity exercise or 75 minutes of vigorous exercise per week is recommended. For strength training, the AHA recommends exercising each muscle group—one set of 8 to 12 repetitions per muscle group, working to fatigue—at least two times a week with two days of rest between sessions. Your own goals may sit above that, whether that’s improving overall health, increasing fitness or training for a race, and they may not match anyone else’s.
There’s no one-size-fits-all number of weekly minutes that means you’re on the right track. The key is getting to know your body and listening to it, as well as being honest with yourself about why you’re hitting the gym or the trails in the first place.
These questions can help guide your approach:
- Are you recovering? Persistent fatigue, frequent injuries or dread of workouts you usually enjoy can be signs that you’re running a deficit between training and recovery.
- Are you fueling? If you’re training hard and routinely ignoring hunger, that’s worth addressing. Eating enough is part of training, not a failure of discipline.
- Why are you doing it? If exercise feels compulsive or is mainly a way to control your body or your weight, consider talking to a health care provider or a dietitian.
- Does your routine include both? Cardio and strength do different jobs, and they support each other.
And if what you’re hearing online sounds extreme, whether that’s “never run again” or “never take a rest day,” it’s often worth checking in with someone who works with real athletes and patients before overhauling your routine.
Our Expertise
Kylee Van Horn is a trail runner, podcaster and endurance sports dietitian based in Carbondale, Colorado.
Tamanna Singh, MD, FACC is a board-certified sports cardiologist, director of the Sports Cardiology Center, and cofounder and co-director of the Women’s Integrated Sports, Exercise, & Research Center (WISER) at Cleveland Clinic in Cleveland, Ohio. She is also a medical advisor for Runner’s World, and an avid marathoner and strength trainer.