Controlling Muscle Breakdown

The hormone cortisol is definitely one of the least understood, but most crucial hormones to consider during a training program. Learn more.

The hormonal response to training is without a doubt one of the top factors to a successful training program. Unfortunately, it is also one of the most complex variables. For this reason, the hormonal factor in training is often either misunderstood, or simply not considered. This is an error that can have detrimental consequences to a training program. In this article, we will turn much needed attention to the muscle-eating hormone cortisol.

The hormone cortisol is definitely one of the least understood, but most crucial hormones to consider during a training program. Cortisol is a hormone released from the cortex of the adrenal glands. Cortisol is catabolic, which means it works AGAINST testosterone, hGH and IGF by BREAKING DOWN the proteins in your muscles and organs and using the amino acids that are released for energy. For this reason, SUPPRESSING cortisol as much as possible is the goal in training.

The Cortisol Hormone:

  • Increases levels of enzymes that break down protein into amino acids
  • Inhibits protein synthesis
  • Converts amino acids to carbohydrates (gluconeogenesis)
  • Accelerates the mobilization and use of fat for energy during exercise

Cortisol And Training Style

Every person that has ever trained for a sport or activity knows that certain styles of training elicit specific results. For example, it is widely known that weight training is the preferred training method for increasing muscle mass and strength, while one must train aerobically to minimize body fat and increase cardiovascular endurance. But why is this the case? The answer can be found when we look at the hormonal responses that each style of training produces.

Aerobic training stimulates a lower testosterone, and a higher cortisol response following a training session when compared to weight training. At the hormonal level, this is why aerobic training is very limited in making muscles grow in size. This response can be physiologically justified when we take into account smaller muscle fibers are more aerobically efficient.

For this reason, muscle fibers (especially type 1) respond SPECIFICALLY to the training stimulus by NOT growing larger, and in some cases SHRINKING in size so that they can function most efficiently for aerobic work. This is why too much aerobic training during a muscle or strength building program can limit gains in strength and muscle mass. (3)

In the opposite manner, weight training produces a much higher testosterone response, and lower overall cortisol response than aerobic training, which is the sole reason that weight training makes your muscles hypertrophy (grow), while aerobic training typically does not. (3) The reason the body responds hormonally to weight training in this fashion is because larger muscles are needed to produce the strength and anaerobic endurance that is required of this type of activity. Again, we see the body's hormonal response is SPECIFIC to its adaptational needs.

Glycogen Is Down, Cortisol Is Up

Probably the most important point to remember about cortisol and diet is that when glycogen (stored carbohydrate) in the body gets low, cortisol levels rise. This makes perfect sense when you keep in mind that carbohydrate is your body's preferred source of calories. When the body does not have enough precious carbohydrates available, alternative sources of energy must be found. The only other options the body has for calories are fat and protein. Rising cortisol levels will speed up the breakdown of lean tissue (protein) in your body and convert the released amino acids into glucose (carbohydrate) for fuel. At the same time, rising cortisol will speed up the release of free fatty acids (from your body fat stores), making more body fat available for aerobic metabolism. (3,4)

Despite the fact that your body may use more fat when your glycogen levels are down, it will also use more muscle. This is obviously an especially undesirable effect for athletes or fitness enthusiasts who require strength and muscle mass for their sport or endeavors. Further complicating the problem, reduced muscle mass will slow the metabolism, ultimately HINDERING further fat loss efforts despite the immediate increase in fat burning.

If you want to maximize muscle mass, strength and body composition over the long term, you need to keep your glycogen levels as full as possible. This means that you need to make carbohydrates (preferably from complex sources) the greatest source of calories in the diet, and eat them with every meal. It means that you should replenish your depleted glycogen stores immediately after exercise to lower elevated post-exercise cortisol levels, best accomplished by taking a high-glycemic carbohydrate meal or drink as soon as possible after a workout.* (1,2)

More Is Not Always Better

Many people train with the philosophy that more is always better. "If you can get that much development from 8 sets, than 16 sets will produce twice as much." Unfortunately, weight training follows the law of diminishing returns, which means that you get the most gains from the first set of exercise, and less and less benefit from each set thereafter. What can happen when you follow the "more is better" rule too closely? A possible result is continuously elevated cortisol levels; a condition commonly referred to as overtraining. Too much and too frequent training can actually cause an overtrained state and a REDUCTION in muscle size and strength via elevated cortisol, proving that in strength training, sometimes more can be WORSE.

Always think of your training in terms of QUALITY, not QUANTITY. Huge training volumes only put a Band-Aid on poor training technique. Knowing and adhering to the principles, good form in the exercises, high mental focus and intensity, proper rest and proper periodization eliminate the need for an extreme amount of training volume to get great training results. In addition, following these rules might even HELP your progress by keeping average cortisol levels lower.

Indeed there is a lot to know about hormones and training. In previous articles, we have examined several of the anabolic hormones and how various training styles and techniques can manipulate the hormonal response for specific outcomes. Really no discussion on hormones and training would be complete without understanding at least the key points of the cortisol response. After all, if you fail to control cortisol levels, all of the anabolics in the world cannot stop the loss of lean body mass and strength that will result.

Semi-indirectly, I have shot down the validity of low carb/high protein diets in this article because of the cortisol response that glycogen depletion causes. The point was presented that high cortisol levels can be beneficial in increasing the use of fat as a fuel source. This, in itself, would seem beneficial to those interested in fat reduction or improving body composition. It would indeed be beneficial if the loss of lean body mass was not, at the same time, so devastating to body composition and fat loss in the long run. Remember that losing lean body mass slows the metabolism, which can promote weight gain in the future. In addition, because body composition (body fat percentage) is a ratio of fat weight to lean body weight, the loss of lean body mass alone can increase body composition measurements.

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Kraemer et al. Hormonal responses to consecutive days of heavy-resistance exercise with or without nutritional supplementation. Journal of Applied Physiology. 85 (4):1544. 1998.
National Strength and Conditioning Association, Essentials of Strength Training and Conditioning, 2nd ed. Champaign, IL: Human Kinetics. 2000.
Wilmore, J.H. Costill, D.L. Physiology of sport and exercise, 2nd ed. Champaign, IL: Human Kinetics. 1999.

* Ingesting a high-glycemic solution immediately after a workout may have the additional benefit of increasing the post-workout hGH and IGF response, but also carry the drawback of decreasing the testosterone response. (2) This may suggest that strength exclusively athletes may wish to wait an hour after a workout before eating, while those trying to gain lean body mass may benefit more from an immediate post-workout meal containing high-glycemic carbohydrates. (1)