I love strength training, and I always have. Give me a barbell, some weights, a couple of dumbbells, and a few bands, and I’ll be one happy fellow. But, I recognize that people also enjoy cardio. As someone who used to run for a time, I remember the allure.

In that line of thinking, I’ve gotten this question a few times before: “Does cardio burn muscle mass?”

Let’s see.

Does Cardio Burn Muscle?

The question, “Does cardio burn muscle mass?” implies that aerobic exercise alone is the problem, which is rarely the case in the real world.

To give you some context, we’ll briefly review a 2012 meta-analysis of 21 studies (1). In it, researchers found that combining cardio and weight training improperly can result in up to:

• 31 percent lower muscle growth rates
• 18 percent lower strength gain rates

Researchers concluded, “Our results indicate that interference effects of endurance training are a factor of the modality, frequency, and duration of the endurance training selected.”

How aerobic exercise impacts our strength training depends on the type of cardio we do, how often we do it, and how long each session is. These findings make sense when you think about it. It’s one thing to cycle for an hour per week and a whole other to run for 40 minutes five days each week.

For most people, cardio won’t necessarily lead to muscle loss, so long as the person eats enough calories and protein (2).

Cardio’s Effects on Muscle Growth And Strength Gain

On the one hand, we have the interference effect. Aerobic exercise is different from weight training, and the metabolic processes it stimulates aren’t necessarily good for muscle growth.

On the other hand, we can argue in favor of aerobic exercise and its positive effects on our weight training results. Most notably, we need some basic endurance to go through our weight training. If you stop sets because you’re getting winded, you’re leaving gains on the table.

This is because lifting weights is more aerobic than most people realize, especially when doing full-body exercises like squats and deadlifts (3). Whether you like it or not, you need some endurance to train effectively.

Besides having essential endurance to do individual sets, we need decent conditioning to recover sufficiently between sets and workouts. For example, if it takes you several minutes to bring your heart rate down after an average set, you have two options:

• Spend nearly two hours per workout to do your sets in a relatively recovered state
• Try to rest for the recommended periods, but risk getting too tired and unable to do enough repetitions (4)

Research shows that good endurance allows us to recover better between individual sets and workouts (5). So, while many people avoid cardio for fear of losing their hard-earned gains, not doing any cardio is also not an option. Instead, we should consider how we can include some cardio into our training without negatively impacting muscle growth.

How to Do Cardio Without It Interfering With Your Muscle and Strength

1. Be Mindful of The Type

Your first consideration for mixing cardio and weight training should be for the activity you choose. There are plenty of ways to get aerobic, so you should consider which has the smallest impact on your recovery and lifting performance.

Low-impact choices like cycling on a stationary bike seem best (1). Such activities still tax your aerobic system considerably and deliver many benefits.

2. Be Mindful of The Duration

Here is what I recommend:

Start with a couple of 20-minute low-intensity weekly sessions, do that for a few weeks, and monitor your recovery. Take note of:

• How you’re feeling
• How you’re performing at the gym
• If you’re experiencing more soreness
• If cardio-related aches are preventing you from lifting weights

You can gradually bump it to an hour of cardio per week. I don’t see a need to do more than that, especially since you’re already lifting weights.

3. Be Mindful of The Timing

Many people find it convenient to do their cardio before lifting. Unfortunately, research suggests that doing as little as twenty minutes of cardio before lifting weights can lower your training performance.

In one study, subjects had to perform 20 minutes of treadmill running at four different speeds (6). Ten minutes later, they had to do five resistance exercises (high pull, squat, bench press, deadlift, and push press) for three sets of 6 to 10 reps with 70 to 80 percent of their 1RM. Subjects also got to rest for three minutes between sets.

Subjects who did aerobic exercise before lifting got between 9.1 and 18.6 percent fewer repetitions. Their squat performance took the largest hit, which seems logical, given that your legs get tired on the treadmill.

If you must do cardio around your weight training, do it afterward. That way, you can get the most out of your lifting performance and do some aerobic exercise before going home. It’s not ideal, but it’s better.

In any case, it would be better to do your cardio or rest days, if possible. This will put enough time between your cardio and resistance training, hopefully minimizing the interference effect.

If you can’t do cardio on rest days, space the two sessions by at least six hours (7). For example, do your cardio in the morning, and lift weights in the evening.

Thank you for taking the time. Until next week,
Philip

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