Does Cardio Kill Your Gains? What the Research Really Says (and How to Do Cardio Without Losing Muscle)

“Don’t do cardio, it’ll kill your gains.”

It is one of the oldest lines in the gym. A lot of lifters skip cardio entirely because they are afraid it will eat their muscle or slow their progress.

The research tells a very different story. For most people, cardio does not hurt muscle growth, and it brings benefits that make you healthier and can make your training better. Here is what the evidence says, and how to do cardio the right way when building muscle is your goal.

Where the Fear Comes From

For decades, researchers have studied something called the “interference effect,” the idea that training for endurance and strength at the same time causes your body to get mixed signals, so you end up worse at both.

There is some truth to it at the extremes. If you train like a marathon runner and a bodybuilder at the same time, something will give. But most people are not doing that. They are lifting 3 to 4 days a week and adding a few cardio sessions.

What the Research Says Now

Cardio does not compromise muscle growth or strength for most people. A 2022 meta-analysis of 43 studies (Schumann and colleagues) compared people who lifted alone with people who lifted the same way and also did cardio. Adding cardio did not reduce muscle growth or maximal strength gains. This held true regardless of age, training status, whether the cardio was running or cycling, or how many times per week people trained.

Explosive power is the exception. The same analysis found that explosive strength, like jumping and sprinting power, took a small hit, mainly when cardio and lifting were done in the same session. When sessions were separated by at least 3 hours, that effect went away.

The amount and type of cardio can matter. An earlier 2012 meta-analysis (Wilson and colleagues) found that interference with muscle growth and strength was linked to how often and how long people did cardio. More frequent and longer cardio sessions were associated with smaller gains. In that analysis, running was linked to more interference than cycling.

Some evidence suggests cardio may even help. A 2016 review (Murach and Bagley) concluded that the evidence for cardio interfering with muscle growth is not as strong as people once thought, and that under certain conditions, combining the two may actually enhance muscle growth.

Putting it together: a reasonable amount of cardio is very unlikely to hold back your muscle gains. Very large amounts, especially lots of long runs, may start to cut into them.

How Cardio Gets You More

A healthier heart and a longer life. Cardiorespiratory fitness is one of the strongest predictors of long-term health. A 2009 meta-analysis of 33 studies and more than 100,000 people (Kodama and colleagues) found that each small step up in fitness was linked to about a 13 percent lower risk of death. People with low fitness had about 1.7 times the risk of death compared to people with high fitness. Muscle matters for longevity, but so does your heart.

Better conditioning in the gym. Being in better aerobic shape means you are less gassed on high-rep sets, circuits and leg days, and many people find they bounce back faster between sets and between workouts.

Easier fat loss. Cardio burns extra calories, which can make it easier to lose fat without cutting food as hard. That can help protect your muscle during a fat loss phase.

Easier recovery between workouts. Light activity like walking keeps you moving without adding much fatigue. (See Walking Is Underrated.)

How Much Cardio Should You Do?

The US Physical Activity Guidelines recommend at least 150 minutes of moderate aerobic activity per week, or 75 minutes of vigorous activity, for general health.

If building muscle is your main goal, a practical starting point:

• 2 to 3 cardio sessions per week, about 20 to 40 minutes each
• Mostly easy to moderate effort, where you can still talk in short sentences
• 0 to 1 harder interval session per week, if you enjoy it
• Daily walking on top of that, as much as your schedule allows

If your strength or muscle gains start to stall, your legs always feel heavy, or your sleep gets worse, scale the cardio back a bit before changing anything else.

Which Type of Cardio Is Best?

Easy steady cardio (the talk test): brisk walking, incline treadmill walking, cycling, rowing, the elliptical. This is the foundation. It builds your aerobic base without much fatigue.

Intervals: short, hard efforts with rest in between, like 30 seconds hard and 90 seconds easy, repeated 6 to 10 times. Great for fitness in less time, but more fatiguing. Once or twice a week is plenty when you are also lifting hard.

Lower-impact options for leg day protection: cycling, rowing, the elliptical and incline walking are easier on your legs and joints than long runs. If your legs are a priority, these are a smart choice for most of your cardio. Running is still fine. Just keep the long runs reasonable if muscle gain is your top goal.

When Should You Do Cardio?

• If muscle or strength is your priority, lift first and do cardio after, or do cardio at a different time of day or on a different day.
• Separate them by at least 3 hours if you can, especially if power and athletic performance matter to you.
• Do not put hard leg cardio right before leg day. Pair harder cardio with upper body days or rest days.
• A short 5 to 10 minute warm-up on the bike or treadmill before lifting is fine. That is a warm-up, not a cardio session.

For a deeper look at the order question, see Cardio Before or After Weights? What the Order Actually Changes.

Fuel the Extra Work

Cardio burns extra energy. If you add cardio without eating a bit more, you may end up in a bigger calorie deficit than you planned, which can make building muscle harder. If muscle gain is the goal, make sure you are eating enough to support both. (See Find Your Real Calorie Number in 3 Weeks and How Much Protein Do You Actually Need?)

The Bottom Line

Cardio does not kill your gains. The best research shows that a reasonable amount of cardio does not hurt muscle growth or strength, and it makes your heart healthier, improves your conditioning and can make fat loss easier. Keep most of it easy to moderate, favor lower-impact options if your legs are a priority, lift first or separate the sessions when you can, and eat enough to fuel both. You get the muscle and the engine.

Sources

• Schumann M, et al. (2022). Compatibility of concurrent aerobic and strength training for skeletal muscle size and function: an updated systematic review and meta-analysis. Sports Medicine. DOI
• Wilson JM, et al. (2012). Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research. DOI
• Murach KA, Bagley JR (2016). Skeletal muscle hypertrophy with concurrent exercise training: contrary evidence for an interference effect. Sports Medicine. DOI
• Kodama S, et al. (2009). Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis. JAMA. DOI