Mixing cardio and strength is (in my humble opinion) one of the best thing you can do in your fitness routine. In this article I’ll explain what to think about in order to make these two training modalities complement each other instead of hindering one another.
Does cardio burn muscle?
To better understand the idea (which is no), let's go over how muscles use energy.
Muscles use a molecule called ATP (Adenosine Tri-Phosphate) to produce energy. Your body can create ATP three ways:
Using stored of phospho-creatine in your muscles. This works for a very short time, this is more the way you use energy in the gym
Using good old carbs converted into glucose. Remember that any type of carb you eat transforms into glucose and either goes into your bloodstream, your muscles as glycogen or is turned into fatty acids (fats). Fats, glycogen and glucose are all used to create energy. You predominantly use glucose and glycogen in fitness classes, especially those those involving HIIT workouts and intense gym sessions as well
Using fat stores during low intensity workouts. Fat molecules get broken down and combined with oxygen that you breath in produce ATP and carbon dioxide that your breath out
These three energy producing methods are active all the time. The magnitude at which you rely on each of them depends on the intensity and duration of the workout.
We can see that in order to prevent cardio from cannibalising our hard earned muscle, we need to have enough fat stores and glycogen in our body and muscles and not do prolonged (2 hours+) bouts of cardio.
For the majority of people reading this, who not long distance runners, this should not be a problem as long as you eat in a caloric maintenance or surplus amount.
Cardio vs strength: the rule of specificity
Training specificity is a basic rule stating that our muscles adapt to the workouts we do.
Simply, if you do more cardio, you will be better at doing cardio, your muscles will get more type 1 fibres which are very useful for cardio activities but aren’t very big (not a lot of definition).
If you do more strength and HIIT training your muscles will get more type 2 fibres which are good at doing intense workouts and are bigger than type 1 fibres but are bad at prolonged exercises.
Now we can see the importance of individualized goals and the potential benefits of doing both sorts of training.
Cardio can be very beneficial to any strength routine because it makes our bodies able to recover quicker which in turn helps us handle more training volume which leads to faster results.
Side note on doing cardio to burn calories
Cardio does in fact burn calories, but I do not recommend doing it for purpose alone.
You cannot out-train a bad diet. So if you think that you can just do extra cardio to burn off a nutritional debaucherie you had last night, I personally think that is a counter productive way of using cardio.
To put it in perspective, drinking three cans of beer (a feet most of us can do easily achieve any night of the week) will give us 300 calories. To burn that amount of calories running would take the average person around 30 minutes.
That’s not outrageous, but that’s the beers alone. Think about all the food that usually comes with beers like pizzas, fries and all the other fun foods.
My point is that using cardio to burn calories takes away from other benefits of this training method and from a results perspective doesn’t do much. You eat too much, you burn it off. You haven’t progressed very far, you’re just back to where you were before eating too much.
Why cardio helps build muscle
Having a better cardiovascular system will help you recover faster during and between your strength workouts, leading to faster gym results. This is, simply put, my favourite reason to do cardio.
On top of that, other advantages of cardio training include:
A way to mix up your training, keeping you more engaged on the long term
Increase cardio output (you can do cardio at a higher intensity)
Lower heart rate
Lower blood pressure
Higher insulin sensitivity
Those are the main ones I think are important and should take precedence over merely burning calories.
As long as your cardio workouts don't require days and days of recovery, you can do them any time during the week.
If you enjoy doing long bouts of endurance, I recommend doing them on Fridays or Saturdays so you have a few days to recover before you next gym workout. Or at least, not working out your legs with super heavy weights the day after a long endurance workout.
If you are going to double up your workouts on a certain day, do your strength workout before your cardio. You can still have a great cardio workout after a strength workout but the other way around doesn't work as well.
What kind of cardio should you do?
By now, I hope you can see how this is a very personal question. You can do really whatever sparks joy for you.
If you tend to dislike cardio, I would recommend keeping that type of workout short, under 30 minutes, even 20 minutes will do the trick really.
Pick a type of workout that you can easily do and aim to perform the minimum amount that still yields the benefits listed above.
This could be a simple 20 minutes of zone2 training on the treadmill, stationary bike or rower at the gym.
Going for a 20 min jog is the simplest form of cardio (in my opinion) as you don’t have to go to the gym for it, you don’t need any fancy equipment and you can go as slow as you want.
Any type of HIIT workout classes or fitness cardio are also terrific. These have the advantages of making you part of a community where you can find more encouragement, accountability and motivation than solo workouts.
If you enjoy cardio, your options are almost limitless. Here you will need to decide what kind of balance you want to have between your strength workouts and cardio workouts.
The more energy spent doing cardio, the less energy you’ll have to do strength workouts and work on getting stronger and more defined muscles and vice versa.
For example, if you go for a two or three hour run one day, you may not be able to do a very intense gym workout the next day. You’ll have to organize yourself in a way that you can align your training with your goals.
My recommendation
For the average person, who wants to feel their best and perform their best, I recommend at least 2 days of cardio in your week.
Two sessions of zone 2 training will go a long way in your training routine.
Remember during these zone two training you should be able to keep a conversation the whole time. If you feel yourself huffing and puffing to the point you can’t talk anymore, you’re going too hard. Slow down.
Conclusion
For the average person with a proper diet, it takes a Herculean effort for cardio to burn your muscles. Eating in a caloric balance or slight surplus will make sure you have enough glucose and fats to produce energy during your endurance training without negating your strength workout results.
The balance you choose between cardio and strength workout will have a bigger effect on your training results. More cardio will give you more cardio results and less strength results and vice versa.
For the average person, that is as simple as it gets.
Two bouts of easy cardio will be very helpful for anyone who wants to get fitter and I think it will be hugely beneficial to your gym routine.
Any of the workout on my Youtube channel will serve that purpose, although the most important aspect of your cardio training is that you enjoy doing it and you are consistent with it.
Happy training!
Clem
Great read. Love the way you break this down. Makes planning my workouts easier!!