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How Hormones Effect Your Workout

Chapter 3: Endocrine Responses to Resistance Exercise



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The endocrine system is an important part of keeping our bodies in balance, also called homeostasis.  This system controls glands such as the adrenals which secrete hormones which are chemical messengers in our bodies.  These hormones communicate with specific cells via receptors coded only to that hormone, in this way targeted tissues can be affected rather than the entire body.  In this way the endocrine system can have much more precise control over regulating body functions.  The nervous system and endocrine system are closely linked, in fact there is a name for the study of this relationship called neuroendocrinology.  There are two main types of hormones, those that are detected on the outside of the cells called peptide hormones, and those that are detected in the nucleus known as steroid hormones and thyroid hormones.  Endocrine hormones are delivered by blood, autocrine hormones are used inside the cell they are produced by, and paracrine are produced in one cell and used by another without being transported by blood.  Some hormones do affect all tissues and have multiple functions such as testosterone, and have effects on organs, bones, and other tissues but this chapter is primarily concerned with skeletal muscle adaptations.

Endocrine= relating to glands that secrete hormones

Autocrine= molecules act on the same cell that produced them

Paracrine= molecules act on cells other than the one that produced them


Muscle as the target for hormone interactions

Skeletal muscles are unique in that they are multinucleated, so the proteins associated with them (muscle fibers) will be controlled by multiple nuclei, wow what a pain, that’s like having multiple bosses!  But is works out better in our bodies than it does in the real world because muscles are actually well coordinated in their growth and repair function, the length of a muscle fiber will grow evenly and has no issues with having more than one boss.  How they manage this is by having nuclear domains, or areas that are controlled by certain nuclei which keeps everything neat and tidy.  Hormones are an integral part of the reactions that take place to create muscle growth and remodeling from the damage inflicted through weight training.  The immune response, inflammation, and ultimately the synthesis of new protein fibers is all driven by hormones.  We can see an increase in the amount of actin and myosin filaments and therefore increased muscle size.  We can also see changes in fiber type in myosin heavy chain proteins from type IIx to type IIa which can be useful since these fibers are less prone to tiring.  Changes can take place in other type II and type I fibers as well, driven by either anabolic hormones such as testosterone, insulin and growth hormone or catabolic hormones such as cortisol and progesterone.


Role of Receptors in Mediating Hormonal Changes

Lock and key theory states that a given hormone with interact with a specific receptor, it must be a perfect match in order for the cell to register the hormone and trigger the corresponding action.  Every cell in our body has a receptor site for some type of hormone, this is the basic nature of the endocrine system.  Sometimes a receptor can become non-responsive to a hormone, this is called down regulation of receptor function.  It is even possible for the number and sensitivity of the receptors to change in a cell for a given hormone but this change is not well understood.


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Steroid Hormones VS Polypeptide Hormones

Steroid hormones are fat soluble and they can diffuse through the cell membrane without any active transport. They then move through the cytosol to the nucleus and start interacting with the cell DNA.  Once it finds its receptor, the hormone creates a hormone-receptor complex which creates a shift in the structure of the receptor and causes the hormone to activate.  Polypeptide hormones are made from amino acids and two examples are insulin and growth hormone (HGH).  Polypeptide hormones can integrate with receptors on the outside and on the inside of a cell.  Polypeptide hormones use 3 major signaling pathways,

  1. Cyclic AMP dependent
  2. Cytokine activated (JAK/STAT)
  3. Prototypical growth factor

Polypeptide hormones are not fat soluble and thus cannot penetrate the wall of the cell, they must rely on secondary messengers to get the information inside the cell and effect change.



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Heavy Resistance Exercise and Hormonal Increases

It’s no secret that heavy resistance training increases muscle strength, size and power.  These changes are based on physiological responses driven by our hormones.  Hormone response is acute and happens as quickly as we start exercising, giving our body feedback on exercise intensity, and our physiological state.  We can even change our metabolic rate following exercise through hormone driven changes, such as the after burn effect.  It is the type of work we do that really drives this change, when lifting heavy loads we are going to recruit large motor units and type II fast twitch fibers.  When placed under heavy resistance we will actually stretch the sarcolemma of the muscles and cause an adaptation resulting in greater androgen receptors (for testosterone) in as little as two heavy lifting sessions!  We are getting gains almost immediately with this type of training.

Hormones will be created that are both anabolic and catabolic following an exercise sessions and if the exercise session was too intense, the catabolic hormones may interfere with the anabolic hormone response.  This is why we have to manage our intensity, it is good to train hard, but it is possible to have too much of a good thing.  The amount of hormone response depends on the amount of muscle that was stimulated, and how much tissue damage/reformation there was.  Only tissues affected by training will benefit from the hormonal response, but research also indicates that even the specific exercises and angles affect the hormonal response.  This means that we need to use multiple exercises from multiple angles in order to fully stimulate the entire muscle and ensure complete growth.


Mechanisms of Hormonal Interaction

We do have a genetic limitation in our muscle cells for size and strength (unfortunately), so if a cell is at this limit, it becomes desensitized to hormonal influence.  This can also happen in muscle cells when there is disease present.  A muscle cell can even become burnt out from chronic levels of anabolic factors, such is common with drug use.  But the main influence is from cellular heredity, we cannot be more than what our DNA is capable.  Exercise intensity dictates the hormonal response in the local area that has been worked, and can have a net anabolic or catabolic effect.  For this reason we need to make sure out exercise prescription is on point and that we maximize anabolic factors while minimizing catabolic ones.


Hormonal Changes in Peripheral Blood

We can get a sense of what is going on inside the cell by testing the blood, but several factors affect what we see in the blood vs what is actually going on in the cell, such as:

  • Fluid Volume Shifts
  • Tissue Clearance Rates
  • Hormonal Degradation
  • Venous Pooling of Blood
  • Interactions with Binding Proteins in the Blood


Adaptations in the Endocrine System

With our strength training program, what we are most likely trying to achieve is a training effect in the muscle and soft tissue.  However, the endocrine system does adapt as well, in the following areas.

  • Amount of synthesis and storage of hormones
  • Transport of hormones via binding proteins
  • Time needed to clear hormones through liver
  • How fast hormones degrade
  • How much blood volume shift there is during exercise
  • How tightly the hormone binds to its receptor
  • The number of receptors in the cell
  • The strength of the signal received
  • How much protein the nucleus instructs the cell to make from hormonal interaction


Primary Anabolic Hormones

Testosterone is the key androgen hormone that interacts with muscle tissue.  It exists in both men and women but in different proportions.  Dihydrotestosterone is the primary androgen that interacts with sex linked tissues (ie. Prostate in men).  Enzymes such as 5 alpha reductase convert testosterone into dihydrotestosterone.  This only happens is sex linked tissues however, and does not happen in the muscle, in this way testosterone can have different effects on different parts of the body.  Testosterone can have effects on the body in other ways as well, such as causing the pituitary gland to release growth hormone.  Testosterone can also interact with motor neurons and cause changes to the number of neurotransmitters and structural protein changes which can increase force production of the muscle and therefore size and strength as a result of increased work output.   After testosterone is released from the sex hormones, they are transported to the cells by sex hormone-binding globulin.  They then pass through the cell and bind to the nuclear androgen receptor and then pass into the nucleus and bind to the DNA, and then the changes are made.

High intensity aerobic training for extended periods has been shown to stimulate testosterone release, but it is also shown to have an overall catabolic effect.  The release of testosterone may be due to the need to resynthesize protein to keep up with protein breakdown.  In fact, aerobic work may cause decreased muscle size due to the need for increased oxidation.  This need for increased oxidation results in reduced cross section in the muscle, the mechanism for this is not fully understood.  Also, we can see a much higher increase in testosterone in younger males with the right types of training.  Variables such as lifting at 85-95% of 1 rep max, brief rest periods, (30-60 seconds), moderate to high training volume, 2 years of weight lifting experience and most importantly large muscle group exercises such as deadlifts, squats and power cleans.

It has been found that younger men have both more free-testosterone and total testosterone in their bodies post workout.  This would increase the likelihood of these hormones interacting with target tissues and creating positive adaptations.  In either case, the release of these hormones seems to be driven by several factors that center around exercise intensity.


Growth Hormone

This is an important hormone for growth, it is produced by the anterior pituitary gland and causes increased amino acid uptake into the cells and causes hypertrophy of muscle fibers.  It has other effects as well such as increases collagen production, increasing fatty acid utilization, decreasing glucose utilization, decreasing glycogen production and more.  In general, growth hormone works by attaching to plasma bound GH receptors on target cells.  We have the most GH at night when we sleep, and while we sleep GH interacts directly with the cell.  It stimulates the release of insulin growth factors and also increases availability of amino acids.  Growth hormone has many effects on many systems, and so it is not recommended for pharmacological use.  If you were to take just GH you may see an increase in muscle size but you might not see an increase in strength due to lack of neural factors.  Use of GH as a type of supplement of still being studied.

Research has shown that not all resistance exercise is created equal for eliciting release and utilization of growth hormone.  If a low percentage of 1RM is lifted, say 26% with much higher repetitions and with greater rest periods, such as >3 minutes, the GH release will not occur.  In one study, the best results were seen with 1 minute rest and 3 sets of 10RM.  We have to keep this in mind if we want to have a strong GH response from our resistance training.


Insulin-Like Growth Factors

Insulin-like growth factors are peptides that mediate some of the effects of GH.  IGF are secreted by the liver after GH tells the liver to make it, thyroid hormone and testosterone are also involved in the regulation of IGF.  IGF travel around the body through the blood by binding to (guess what?) binding proteins (BP), they ride along with these BP until they get to the target tissue, hop off and attach to the target receptor.  There are six distinctly different BP and all act slightly different in response to the stress of exercise.  The release of IGF has been shown to create its own BP from within the muscle cell.  The more it is produced, the more BP for it there is, the more response we can get.


Adrenal Hormones


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There are two main parts to the adrenals, the cortex and the medulla, and both can have adaptations from exercise.  The cortex is the outside of the adrenal and is stimulated by a chemical called ACTH from the pituitary gland.  The inside medulla is stimulated by our nervous system and this allows it to have a faster response time.  There are three important hormones secreted by the adrenals; cortisol, catecholamine’s, and encephalin-containing polypeptides.  Cortisol is primarily a signal hormone that tells the body to metabolize carbohydrates, even though it gets a bad rap in the muscle game.  But cortisol does break down muscle tissue, and it seems to do this more in type II fibers compared to type I.  Type I fibers seem to rely more on a reduction of protein breakdown in order to hypertrophy whereas type II fibers rely on a massive increase (respectively) in protein synthesis in order to hypertrophy.  Cortisol does most of its damage you could say, by converting amino acids to carbohydrates, this is muscle breakdown.  This happens due to the increase in proteolytic enzymes they lyse or breakdown proteins, hence the name.  Cortisol will be stimulated for the same conditions that GH will, that is, intense bouts of heavy exercise with minimal rest, these are optimal conditions for cortisol release.  It is interesting that these very different hormones are stimulated by the same type of exercise stimulus, this leads researchers to believe that they have a harmonious relationship as an exercise response that is part of muscle remodeling on a larger scale.  These hormones have multiple roles so it is not as simple as finding ratios to determine if an athlete is overall catabolic or anabolic, more research needs to be done to better understand this duality.  But what we can say, is that while chronic levels or cortisol may be catabolic, acute levels as a response to exercise may be crucial for muscle remodeling.



Norepinephrine, epinephrine and dopamine are important for muscle strength because they turn on the muscle from a neurological standpoint and also increase blood vessel dilation in the periphery.  These are secreted from the medulla of the adrenal glands.  These hormones increase force production in working muscles and also turn on other hormones.  When considering training responses we must make sure our training stimulus is varied, if not the adrenals do not get a chance to “stand down” and make their recovery process and we can suffer from catabolic burnout.

In conclusion, to get the best responses for GH, testosterone and adrenal hormones, we want our training to be heavy, moderate to high volume, using big multi-joint movements, and varied over time.





Baechle, Thomas R. Roger, Earle W. (2008). 3rd Edition. ESSENTIALS of STRENGTH

TRAINING and CONDITIONING. National Strength And Conditioning Association.


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