Should You Do Cardio in the Bulking Phase?

Should You Do Cardio in the Bulking Phase?

In the field of bodybuilding, aerobic exercise, also known as “cardio”, has been reduced to a tool to increase energy expenditure in order to reduce our fat percentage more quickly or to generate create calorie deficits

Cardio only in the Cutting Phase?

Cardio is traditionally performed in the cutting phase, falling into oblivion in the bulking or muscle mass gain phases, because if our objective is to generate a calorie surplus to provide energy for the protein synthesis processes, why would we increase our energy expenditure? Seems counterproductive, right?

The Importance of Cardiovascular, or “Cardio”

Aerobic exercise has proven to be an important tool to increase our cardiorespiratory capacity and physical fitness, being a catalyst to reduce the risk of mortality from cardiovascular diseases and cancer, amongst others, with a negative correlation between physical fitness and risk of mortality from all causes (Blair et al. 1989).

Low-intensity aerobic exercise, which is what I recommend as the first port of call at any time of the season, as it’s what will help us generate the reduced interference phenomenon when our goal is to gain muscle mass, producing less nerve stimulation, and is what predominantly uses fatty acids as an energy substrate.

In this article, I’m going to explain my unorthodox view of cardio and why I think it’s important to do all year round, in both bulking and cutting phases.

Importance of Cardiovascular Exercise, or "Cardio"

As a backdrop to the article well and to avoid having to repeat concepts, I recommend you read my latest article on fatty acid oxidation first.

In the article on fatty acid oxidation I talked about mitochondria, the cellular organelle where fatty acids undergo a process called beta-oxidation, that is, where we “burn fat”

Does Load Training Hinder Fat Loss Efficiency?

Some research supports the hypothesis that weight training can damage the mitochondria, reducing their number and size, mainly due to mechanisms induced by generation of reactive oxygen species and local hypoxia caused by repeated muscle contractions that increase “cellular swelling” (better known as pump).

(Webster, 2009) tells us about how reactive oxygen species can initiate the process of mitochondrial damage, damaging membrane permeability.

Does Load Training Hinder Fat Loss Efficiency?

In addition to seeing how the decrease in pH, which causes acidosis induced by the prominence of anaerobic lactic metabolism (predominant in weight training), can damage the capacity to produce ATP in the mitochondria, altering the ionic gradient across the membranes and producing cell death (cell necrosis).

The mechanisms by which this process can occur are complex and have been studied in severe cases of heart attacks or cardiovascular disease. We do not know the extent to which voluntary acidification (through physical exercise) can affect the integrity of the mitochondria, but we can take it into account.

Does Aerobic Exercise Improve Fat Burning Efficiency?

However, exercise with a predominantly aerobic metabolism, such as walking or running at low intensity, is an important tool to promote mitochondrial biogenesis, which is the process by which the size, number, content and activity of the mitochondria increase.

This, according to (Hood, 2009), is due to the activation of certain proteins resulting from physical exercise that activates mitochondrial gene expression, resulting in an increase in the mitochondrial network and a greater ability to produce ATP.

Aerobic exercise must be conceived as the counterweight balancing the “damage” produced in the bulking phase: intense workouts, such as those mentioned above, can affect cell integrity.

Does Aerobic Exercise Improve Fat Burning Efficiency?

Such sessions are harmful to our mitochondria, and a smaller number of mitochondria equals a smaller number of “ovens” available for fat burning.

The result will be a greater fat gain in bulking phases and a greater effort required for its loss in cutting stages.

Should you do Cut Out Cardio in the Bulking Phase?

Not at all.

It’s as simple as including small aerobic physical exercise sessions on a regular basis to keep fat at bay, even when bulking.


  1. Webster, K. A. (2009, September). Mitochondrial Death Channels. American Scientist.
  2. Hood, D. A. (2009). Mechanisms of exercise-induced mitochondrial biogenesis in skeletal muscle. Applied Physiology, Nutrition, and Metabolism = Physiologie Appliquee, Nutrition et Metabolisme, 34(3), 465–472.
  3. Blair, S. N., Kohl, H. W. 3rd, Paffenbarger, R. S. J., Clark, D. G., Cooper, K. H., & Gibbons, L. W. (1989). Physical fitness and all-cause mortality. A prospective study of healthy men and women. JAMA, 262(17), 2395–2401.

Related Entries

  • Maximising Fat Burning
  • 7 Cardiovascular Benefits of Physical Exercise You Didn't Know
  • Cardio for Fat Loss
Review Cardio in the Bulking Phase

Only in Cutting - 100%

Importance of Cardio - 100%

Aerobic Activity - 100%

Doing less during cutting - 100%


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About Alfredo Valdés
Alfredo Valdés
He is a specialist in metabolic physiopathology training and in the biomolecular effects of food and physical exercise.
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