Can Cardio Waste Muscle?

The short answer – Yes. Losing body fat while maintaining your hard-earned muscle can be a challenge. A lot of people whose goal is fat loss tend to choose all the highest intensity versions of working out because they think “the harder I go, the more calories I burn!”. They also often couple this with eating less to hopefully further maximize their results. The problem is, you still have to factor in muscle.

What We Don’t Realize About Overdoing Cardio
Our bodies are built for survival. When under stress (i.e., high intensity workouts) and when underfed (i.e., eating fewer calories) our bodies enter a type of survival mode. In order to “save your life”, it starts prioritizing what’s important and what’s not. The whole reason we have body fat is because back in the day, we might have gone days without food. When you’re eating too little calories and doing 5+ days of cardio your body is thinking the same thing. Since fat is a very good energy source, it’s prioritized higher and held onto.

Muscle costs a lot of calories to maintain and after some time will be prioritized lower since it’s more “expensive”. Our bodies will start breaking down muscle tissue (expensive) and holding onto fat (cheap), in order to provide energy. Loss of muscle will slow our metabolism in the long run.

The worst thing a person can do is unfortunately what we see a lot of. HIIT training multiple times a week or running at a moderate to hard pace for long distance every day. Either of these paired with low caloric intake are recipes for wasting muscle and storing body fat long term.

The Solution
Lift heavy weights

Back to the “survival” idea. Our bodies only break down muscle for energy if it doesn’t feel there’s a need for it (e.g., when all we do is run). However, if you give it a proper stimulus, such as resistance training with weights where you hit your full body, with different exercises, while staying 1-2 reps short of failure each set, our body is forced to hold onto muscle. It realizes it is needed for “survival”. Proper resistance training sends signals to our body, “Hey, we better keep this muscle so we can withstand this stress being placed on our muscles!” Even if muscle gain isn’t your goal, there is no sense in losing the muscle you currently have. It’s the best insurance plan for health and longevity.

Do full body workouts 3-4 times a week, prioritize compound movements, and end each set ~2 reps shy of failure. For cardio, add in 10-15 minutes of sprint style cardio to elicit more hormone (growth hormone, testosterone, IGF-1) response and encourage the body to spare muscle tissue. Outside the gym, consider increasing your non-exercise activity thermogenesis (NEAT) activity. Focus on hitting 8,000 – 10,000 steps throughout your day. Adding 1,000 steps each week is one way to progress and increase NEAT.

To support lean muscle tissue and encourage fat loss, focus on resistance training while approaching cardio intelligently. Dial in your nutrition by eating whole, non-processed foods aiming for ~1 gram of protein per pound of lean body weight to support muscle repair and recovery. Consume moderate to low amounts of carbohydrates mostly from fruits and non-starchy vegetables, and adequate fats from animal sources (limit or avoid seed and vegetable oils).