Is Low Intensity Cardio the best way to burn fat while bulking?

I don’t know why it is but we Hardgainers are so selfish.  We want to bulk up, gain muscle mass and rid ourselves of our skinny frames while maintaining our defined look. Some argue that you can’t have the best of both worlds and that you must choose between bulking or cutting but I tend to think differently.

The general recommendation for Hardgainers is to stay away from cardiovascular exercise. This being because we have hyperactive metabolisms and we can’t afford to loose any more weight. Although its very possible to stay lean with a great diet alone for most of us this is not realistic. As we start to put on the pounds those defined abs are not as defined as they used to be and your lats don’t seem to look as separated as before.

What are we to do?

I’m going to breakdown what occurs when using high intensity cardiovascular exercise and low intensity exercise and how this effects fat metabolism.

Fuel use during exercise

The Fuel source used during cardiovascular exercise is dependent on 4 things.

1. The intensity of exercise
2. The duration of exercise
3. The fitness level of the exerciser
4. Pre-exercise nutrition

1. Fuel Use: Effect of Intensity

How hard we work during cardiovascular exercise is an important indicator as to what our body will use as energy. High intensity exercise uses carbohydrates primarily as its fuel of choice while low intensity exercise uses fat.

Why is this so?

• Well, As exercise intensity increases the body needs make ATP at a faster rate. Carbs are metabolized a hell of a lot fat than fat so naturally they are used first.
• Additionally during high intensity exercise cells lack the oxygen needed to breakdown fat into its usable form for ATP production so once again the body relies on Carbohydrates.
• During High intensity exercise more fast twitch fibers in the muscle are recruited. This type of fiber prefers to use carbohydrate as the primary fuel source, another reason why carbs are used more than fat.
• Lastly during high intensity exercise specific hormones are released that stimulate the break down of glycogen (stored carbs) to be used as ATP.

Bottom Line: Fats are the primary fuel source during low-intensity exercise and Carbohydrates are the primary fuel source during high intensity exercise

2. Fuel Use: Duration

Generally speaking when you partake in cardiovascular exercise lasting more than 30 minutes our bodies shift from using Carbohydrates to Fat as a Primary Fuel source.

This occurs because as time passes our glycogen stores in our muscles are depleted. This results in there being a minimal amount of glucose and glycogen available to be used in glycolysis. A chain reaction begins and since glycolysis cannot occur there is no available pyruvate for the Kerbs cycle. With this ATP producing pathway shut down the body must use something to create ATP (energy). The body thus turns to fat as its backup fuel source.

Bottom Line: During prolonged exercise there is a greater reliance on fat.

3. Fuel Use: Fitness Level of Exerciser

People who are in better shape burn fat easier. This is a bonus for us because we already have crazy hyperactive metabolisms. With increased fitness level our ability to burn fat increase.

Why are trained people better fat burners? Well simply put, trained people are better fat burners because:

1. They have more mitochondria (mitochondria use fat to make ATP)
2. Trained people use oxygen more efficiently (oxygen is used to breakdown fat)
3. Train people have favorable enzymatic difference that allow them to burn fat easier

Bottom Line: Fit people are efficient fat burners

4. Fuel Use: Pre-exercise nutrition

What you eat before a cardiovascular session will effect what fuel source is used during exercise. The more carbohydrates you have before exercise the more your body will rely on them as a fuel source during exercise.

This is one of the reasons why some people do light intensity cardiovascular exercise in the mornings on a empty stomach. The logic is that since in the more our glycogen stores are just about depleted our body has no choice but to burn fat.

This method does work but I wouldn’t recommend it. (Well not at least until I research the Pro’s and Con’s of this approach)

Bottom Line: What you eat before cardiovascular exercise will affect what fuel source is used.

Based on the above information we can now come up with a General Rule

• Lower intensity, longer duration exercise relies more on fat as a fuel
• Higher intensity, shorter duration exercise relies on carbohydrate as a fuel

So does this mean for Hardgainers?

It’s really up to you if you’d like to incorporate cardiovascular exercise into your current workout routine. Besides fat burning there are tons of life long benefits associated with it. I would recommend adding at least 1 or 2 30 minute low intensity sessions a week. But if you are struggling to put on the weight (like myself at the moment) be mindful of how much time you put towards cardiovascular exercise (if any at all).

Reference: Howley, E., & Powers, S. (2007). Exercise Physiology: Theory and Application to Fitness and Performance. New York: McGraw-Hill.