By Jordan Ahlstrom

Why No Cardio? Is cardio bad for muscle gain?

The vast majority of people engaging in “cardio” exercise do so to reduce their body fat. This may be one of the worst approaches to achieving that goal because cardiovascular exercise up-regulates cortisol.

This has an impact that runs counter to what these fitness enthusiasts want. Cortisol reduces muscle mass and protects body fat so that you keep that fat in your body as a backup energy supply for as long as possible. Basically, your body adapts to its environment and endurance exercise sends a signal that the body needs a substantial energy supply available at all times.

The use of X3, on the other hand, does not increase cortisol like cardio does. Instead, X3 upregulates growth hormone, which can increase tendon and ligament repair, accelerate the loss of body fat, and increase general fitness levels.

Some people also engage in cardio because they want to promote cardiovascular health. It’s not well publicized, but research has repeatedly shown that strength training promotes the same or greater changes on cardio related health metrics. This is discussed at length in our book, “Weight Lifting is a Waste of Time.” (

Related research Cortisol is upregulated in endurance exercise. This sacrifices muscle in favor of protecting body fat. Schwarz, L., & Kindermann, W. (1989). β-Endorphin, catecholamines, and cortisol during exhaustive endurance exercise. International journal of sports medicine, 10(05), 324-328.

Higher cortisol levels are associated with muscle loss. Peeters, G. M. E. E., Van Schoor, N. M., Van Rossum, E. F. C., Visser, M., & Lips, P. T. A. M. (2008). The relationship between cortisol, muscle mass and muscle strength in older persons and the role of genetic variations in the glucocorticoid receptor. Clinical endocrinology, 69(4), 673-682.

Higher cortisol levels contribute to faster and longer lasting body fat storage. Moyer, A. E., Rodin, J., Grilo, C. M., Cummings, N., Larson, L. M., & Rebuffé‐Scrive, M. (1994). Stress‐induced cortisol response and fat distribution in women. Obesity research, 2(3), 255-262.

Over 100 studies analyzed (known as a meta-analysis) show brief, high-intensity interval training to increase endurance as much as, or more than, traditional endurance training. Importantly, duration appears to be less important than intensity. These data suggest that the shorter duration and higher intensity of resistance training may give it an advantage over intervals in building cardiovascular fitness.

Steele, J., Fisher, J., & Bruce-Low, S. (2012). Resistance training to momentary muscular failure improves cardiovascular fitness in humans: a review of acute physiological responses and chronic physiological adaptations. Journal of Exercise Physiology Online, 15(3), 53-80.