It is often thought that too much cardio exercise can cause you to burn muscle, and that there is a “boiling point” of cardio time where you begin to start eating into your gains.

This has been shown to not be the case. The reason that cardio has gotten a bad reputation for burning muscle, is that more often than not, people couple cardio with drastic diets in their effort to “cut”. If you don’t consume enough protein and enough calories, your body will cannibalize your muscles.

So if people have been noticing loss of muscle mass it may very well be the diet that’s causing them to lose muscle mass, not the cardio! Cardio exercise can actually help you to increase muscle mass, and I’ll explain how.

Cardio can help you BUILD muscle

One of the reasons is that cardio can aid recovery. After an intense workout, DOMS (Delayed Onset Muscle Soreness) can often set in. That’s the ache and the stiffness you feel in your muscles for the next 24-48 hours. DOMS can hinder your strength training as well as your motivation to train.

Doing 20-30 mins of daily cardio can alleviate the symptoms of DOMS by increasing circulation and nutrient flow in the muscle to help them rebuild faster. I personally find the day after a tough workout, a quick run really loosens me up ready for my strength workout.

When does cardio burn muscle?

There are some rare occasions when cardio will burn muscle. If it’s the only energy source available, your body will have to burn muscle to survive. When your body fat percentage is so low, your body has no chance but to begin burning muscle. This problem however, only really affects bodybuilders in the final weeks before a competition.

Overtraining can also cause you to burn into muscle stores. A study published in Germany¹ tested athletes who ran an average of 43 miles a day for 64 days for a trans-Europe run. The runners lost large amount of fat, which is to be expected, however loss of muscle mass in the legs was recorded. This is due to an overtraining effect on the legs due to the massive exertion. It’s important to note that no muscle mass was lost on their upper bodies.

It’s a common misconception that cardio can burn muscle mass, this is not always the case.

Finally, if you are not consuming enough protein your body will burn muscle. This is often caused by the aforementioned crash diets. If you drop your caloric intake more than 20% below your TDEE, it is difficult to get enough essential amino acids with the protein you eat. Your body needs daily protein to replace and repair muscle cells, even when you don’t lift weights.

In summary

Proper nutrition while dieting is key to insuring you don’t lose muscle mass. A good idea is not to reduce your calories by more than 20% below your TDEE (Total Daily Energy Expenditure). There’s no need to abandon park runs or football with your mates just because you want to add muscle mass. Cardio and weights can be perfect allies in supporting a goal to build a bigger physique.