Does Cardio Kill Muscle Gains?
Does Cardio Kill Muscle Gains?

Cardio can be scary for any guy or gal looking to build serious muscle. After all, the idea that cardio kills gains has been circulating the weight room for years. So, is it bad to do cardio if you’re trying to build muscle? The answer: only if you do it the wrong way.

Read on to find out how to keep cardio from messing with your muscle gains.

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How Cardio Might Prevent Muscle Gain

There are a couple of ways cardio can interfere with your gains:

Same-day workouts: If you tackle cardio and strength in the same training session, your body won’t be able to adapt to either activity as well as you’d like it to. “Your goal with exercise is to stimulate your body to adapt,” says William P. Kelley, D.P.T., A.T.C., C.S.C.S. “To keep muscle and cardio gains, you need to give these adaptations time to occur and the tools, or food, prior to throwing another stimulus at it.”

In other words, if you lift heavy and then head out for a run, your body will de-prioritize the strength training adaptations in order to fuel your run.

Switching it up probably won’t help either. If you do cardio before strength training, you may tire yourself out and ultimately limit how much — and how hard — you can lift. In fact, a 2016 study in the Journal of Strength & Conditioning Research found that when a group of healthy men did cardio before strength training, they completed fewer repetitions, had less muscular power, and experienced an increase in perceived exertion during their strength session.

Poor fueling (not getting enough carbs): Cardio can cut into your muscle gains if you do it without fueling properly. And when it comes to cardio, carbs are your best friend: “If your body doesn’t have sufficient carbohydrates at its disposal, it will start to break down proteins and amino acids for fuel, which can negate or slightly reverse muscle growth and gains,” Kelley explains.

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How to Prevent Cardio from Hindering Muscle Gain

Cardiovascular fitness is a key piece of overall health, and aerobic exercise (or a blend of aerobic and anaerobic, a la HIIT) is the best way to achieve this.

So, it’s important to figure out how to incorporate cardio into your routine — without compromising your muscle gains.

  • Take a break between workouts (at least 12 hours): One way to check off the cardio box without derailing your progress in the weight room is to do the two activities on different days, though you may be able to get away with separating the workouts by 12 hours if you’re dying to do both the same day, Kelley says. Sure, you may end up working out more often during the week, but at least you’ll be able to do each workout to the fullest. And your body will have the chance to adapt to each stimulus before tackling another.
  • Proper nutrition is key: It’s also important to make sure you’re fueling properly for your cardio workouts, which means… healthy sources of carbs, protein, and fat. Carbs and fats are the fuel sources your body primarily relies on to create adenosine triphosphate (ATP), the chemical that powers working muscles. “The process of turning protein into ATP is much harder than turning carbs and fats into ATP, so [your body] will take the easier option as long as it’s available,” Kelley explains. Protein is also vital. Whether you’re counting bench press reps or logging miles, your muscles are driving your effort, and they require protein for repair and recovery.
  • Carbohydrates are especially important: Exactly how many carbs you’ll need depends largely on the duration and intensity of the exercise. However, the International Society of Sports Nutrition (ISSN) offers a general recommendation of 5 to 12 grams of carbs per kilogram of body weight per day (g/kg/d). But unless you exercise at a moderate to high intensity for 12 hours per week, stick to the lower and middle portion of the range.

What Kind of Cardio Should You Do?

First, aim to get at least 150 minutes of moderate-intensity cardio, or 75 minutes of vigorous-intensity cardio every week, as recommended by the Centers for Disease Control and Prevention (CDC). Great cardio options include walking, jogging, swimming, cycling, and rowing.

However, if your goal is to build muscle, your best bet may be high-intensity, short-duration cardio (i.e., HIIT), Kelley says. “This method of cardio training actually aids in the muscle growth stimulus as it’s more power-based,” he adds.

Learn more about HIIT and how to incorporate it into your training.