Does Cardio Burn Muscle?

Scooby Biking

Its a well known fact that doing cardio everyday is the most important thing you can do for your health but lets assume you don’t care about your health, lets talk about gaining muscle. I know you are used to hearing that “cardio burns muscle” but I’m going to show you why that’s wrong. Cardio does NOT hurt your ability to gain muscle at all and it might even HELP you to ADD muscle mass.

The reason that cardio has gotten a bad reputation for burning muscle is that most often, people couple drastic diets with cardio in their effort to “cut” after “bulking” – its why I hate the whole bulking and cutting mentality. ) Its the drastic caloric reduction that is responsible for the muscle loss, not the cardio! If you don’t consume enough protein and enough calories, your body will cannibalize your muscles – a good safe limit is not to reduce your calories by more than 20% below your TDEE (Total Daily Energy Expenditure), to find a muscle-safe caloric intake for dieting please use my calorie calculator.Proper nutrition while dieting is key to insuring you don’t lose muscle mass. You can lose weight with an all-twinkie dietbut you will lose lots of muscle at the same time!

So cardio doesn’t burn muscle, but how might it help you GAIN muscle? – Lets look at THREE ways:

  1. DOMS (Delayed Onset Muscle Soreness) is a common result of intense workouts and doing 20-30min of daily cardio increases circulation and the increased nutrient flow by the muscle helps the muscles rebuild faster.
  2. Not every workout plan has 5 minutes rest between sets, some workouts you will need to do to build mass are very taxing to your cardiovascular system. If you don’t constantly work to keep your cardiovascular system running at peak performance there are workouts you just wont be able to do with sufficient intensity to gain mass.
  3. There are intense weight workouts that double as cardio workouts and these go by several names – hybrid workoutscomplexes, etc – and they all have one thing in common, they take compound weightlifting exercises and do them repeatedly for cardio – often as intervals. These hybrid workouts can build muscle and give you a cardio workout at the same time!


Cardio does not burn muscle mass, crash diets and bad nutrition burn muscle mass!
20-40min cardio every day is not only good for your health but it can help you add muscle as well.

There are some situations where muscle gets burned, lets look at those in depth so you can avoid them.

  1. If its the only energy source available, your body will burn muscle to survive. Fat is our bodies energy storage device, our gas tank that enables us to survive when food is scarce. If you haven’t eaten anything AND your bodyfat is dangerously low, then your body has no choice than to burn muscle in order to get the necessary energy to keep you warm and alive. What does your body consider dangerously low bodyfat, for males probably 3-5%. In this low bodyfat situation, your body will burn muscle to provide the energy to keep you alive. Very few of us have bodyfat low enough that we have to worry about this! A very small percent of the population is perpetually skinny (under 3% bodyfat), that is, no matter how much they stuff their face, they cant add an ounce of fat. For these people, they have enough trouble consuming enough calories to survive – doing cardio would burn muscle.
  2. If you are not consuming enough protein your body will burn muscle, this is often the case in crash diets. “Essential Amino Acids” are called essential for a reason, your must eat them in sufficient quantities or your body has no choice other than to cannibalize your muscles to get them. When people reduce their caloric intake more than 20% below their TDEE, it is *very* difficult to get enough of these essential amino acids with the protein you eat. Even when you don’t lift weights, your body needs daily protein to replace the muscle cells which have died. If you don’t eat enough protein, the muscle cells don’t get replaced. If you are doing a crash diet, then doing cardio will increase the muscle loss. DONT DO CRASH DIETS! If you want to know what you can safely cut your caloric intake to, use my calorie calculator.

How Much Cardio Is Too Much?

So 20-40 minutes of cardio a day is good for you and helps you gain muscle, is more cardio better? What I have found with my own personal experience, is that there are four issues that crop up and hinder muscular gains when you do too much cardio:

  1. Short term fatigue. If you play an intense game of soccer or basketball and workout right afterward, you will have a lousy workout and your muscular development will suffer. Your body can only take so much and if you are exhausted from running all over the field, there is no way you can put enough intensity into your workout to make gains. However, if you wait 4-6 hours to recuperate before lifting weights, you weight workout will be just as aggressive and successful as if you hadn’t done the cardio.
  2. Total exhaustion, cardio till you drop. Depending on your conditioning and intensity level, after 3-16 hours you will just konk out. If you have ever done endurance sports, you know exactly what total exhaustion feels like. For me, doing an olympic length triathlon which is about 3hrs of intense cardio puts me on the edge – 4 hours would definitely put me in the total exhaustion category. For my long distance cycling trips, because the intensity is much lower I can go 12-14 hours before reaching total exhaustion. Once you reach total exhaustion, any weight workout you attempt will not be successful. Not only will you be too tired to aggressively push the weights but after the workout, your body will be too busy repairing itself from the brutal cardio session to be able to build up your muscles.
  3. Repetitive motion injuries. Often its not the cardio itself that’s the problem, it’s the injuries. Do anything for more than 4 hours and you are asking for repetitive motion injuries, doesn’t matter if its running, rowing, swimming or cycling. Once your joints are in pain, any possibility of muscle mass gaining weight workouts go out the window.
  4. Overtraining. This is the biggie. If you get too much cardio, the major muscle which has provided your locomotion is essentially doing a mega-rep, low weight workout. If you do 6 hours of squats, you will suffer from severe overtraining and lose both strength and muscle mass. Likewise, if you do two marathons a day you will lose leg mass which leads us to this amazing study ..

Now I know that some of you are STILL worried about cardio burning muscle so lets look at a great study (1,2,3)where they monitored body composition of athletes in the trans-europe run where they ran 2800 miles in 64 days – that’s an average 43 miles a day. The results were really interesting and not what you might expect. Obviously they lost fat and lots of it. The interesting part was that the runners didn’t lose ANY muscle mass in their upper bodies, ALL the mass was lost in their legs – why? Overtraining!!!. So if these athletes can run 43 miles (6 hours) every day all summer long without losing any upper body muscle mass, certainly YOU can jog for 30 minutes without losing muscle mass!

Remember, your body is really smart and it wont burn muscle unless you do something really stupid like running 3000 miles or doing a drastic fad diet.