Reading research: Hormonal Responses and Adaptations to Resistance Exercise and Training

Let’s get the Reading Research series off to a bang in 2012 with this extensive review article about hormonal responses to resistance exercise.

The study is actually a review article and it’s called Hormonal Responses and Adaptations to Resistance Exercise and Training, by William Kraemer and Nicholas Ratamess, Sports Medicine, 2005.

The study covers each of the important hormonal responses to resistance exercise in turn, covering testosterone, growth hormone, cortisol, insulin-like growth factors (IGF), insulin, catecholamines and sundry other hormones.  I’ll follow the same pattern below, although I’ll concentrate on testosterone, growth hormone and cortisol as the most interesting ones.

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Testosterone: an introduction

Here’s a quick introduction to testosterone, if you haven’t been near an exercise physiology textbook recently…

What is testosterone? (source: Wikipedia) - Testosterone is a steroid hormone from the androgen group.  It is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands.

In men, as the principal sex hormone, testosterone plays a key role in the development of male reproductive tissues such as the testis and prostate as well as promoting secondary sexual characteristics such as increased muscle, bone mass, and the growth of body hair.  On average, an adult human male produces about 10x more testosterone than an adult human female, but females are more sensitive to the hormone.

What is free testosterone? The majority of testosterone circulates in the blood bound to a carrier protein, called sex hormone binding globulin.  Bound testosterone does not play an active role in the body.  Only unbound (free) testosterone is able to enter the different cells of the body and exert androgenic and anabolic effects.

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Testosterone: the review article

And here’s what I found out from reading the review article:

There are gender differences – I was interested to note that many studies have shown that resistance exercise increases total testosterone concentrations in men but not in women. So much of what follows may be completely irrelevant for my female readership (both of you!) and may explain much of why women and men have very different responses to training.

Consistent resistance training has a higher effect on testosterone - in the study, Effect of training status and exercise mode on endogenous steroid hormones in men, by Tremblay, Copeland, Van Helder, in Journal of Applied Physiology, 2003, higher elevated free testosterone concentrations were reported following resistance exercise where the subjects were previously resistance-trained men rather than endurance-trained.

Additionally, in the similar study Effects of heavy resistance training on hormonal response patterns in younger vs older men, by Kraemer, Hakkinen, Newton, et al, in Journal of Applied Physiology, 1999, the magnitude of free testosterone elevation was greater after 10 weeks of periodised strength training compared with the pre-training response, thereby suggesting that an extensive period of resistance training may enhance the response of each workout.

Factors affecting the testosterone response - the size of the testosterone respsone to exercise has been found to be dependent on the following factors (where more is better):

• The amount of muscle mass involved
• Intensity
• Volume
• Nutritional intake
• Training experience

However, absolute strength levels do not appear to influence the size of the testosterone response.

Why arm days might be less effective (if you are natural) – in the study The effect of short-term strength training on human skeletal muscle: the importance of physiologically elevated hormone levels, by Hansen, Kvorning, Kjaer, et al, in Scandinavian Journal of Medical Science in Sport, 2001, the researchers measured muscle strength changes in the elbow flexor muscles following 9 weeks of resistance training.

In this study, one group performed a workout consisting of curls only and a second group performed lower-body exercises prior to the curls. So what happened?  Well, performing curls only failed to acutely elevate testosterone significantly.  However, testosterone was significantly elevated when lower-body exercises were performed first, and muscle strength increased to a greater extent as well when both lower- and upper-body exercises were performed.

Why low-volume training is less effective – in the study Acute effects of different intensities of weight lifting on serum testosterone, by Schwab, Johnson, Housh, et al, in Medical Science in Sports and Exercise, 1993, the researchers reported significant elevations in testosterone during two squat protocols.

However, testosterone did not significantly increase until after the fourth set was completed.  I wonder whether this is why lower volume programmes always emphasise large amounts of food?  Perhaps the anabolic response is needed from the food because it is not being achieved from the training volume?

In addition, various studies have shown that when resistance is held constant, the larger acute testosterone response is observed in the protocol consisting of a higher number of sets.

Low-carb or low-fat? I was interested to read that in the study Hormonal responses to consecutive days of heavy-resistance exercise with or without nutritional supplementation, by Kraemer, Volek, Bush, et al, in Journal of Applied Physiology, 1998, the researchers concluded that the testosterone response to resistance exercise appears to be influenced by nutritional supplementation.

In what way?  Well, I was surprised to find that in this study carbohydrate /protein supplementation limited the testosterone response to resistance exercise.  But everyone says take protein and carbs after a workout, right?  So what the hell is going on?

The rationale is unclear but another study reported reduced low circulating concentrations of testosterone in response to low dietary fat intake and a diet with a high protein/carbohydrate ratio.  So perhaps reducing dietary fat is the problem?  Or is it something to do with the insulin response of the carbohydrate?

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Growth hormone: an introduction

Here’s a brief introduction to growth hormone if you need a quick reminder…

Growth hormone (source: Wikipedia) is a peptide hormone that stimulates growth, cell reproduction and regeneration.  Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesised, stored, and secreted by the somatotroph cells within the lateral wings of the anterior pituitary gland.  Besides the obvious, growth hormone produces the following effects:

• Increases calcium retention
• Increases the mineralisation of bone
• Increases muscle mass through sarcomere hyperplasia
• Promotes lipolysis
• Increases protein synthesis
• Stimulates the growth of all internal organs apart from the brain
• Reduces liver uptake of glucose
• Promotes gluconeogenesis
• Stimulates the immune system

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Growth hormone: the review article

And here’s what I found out from reading the review article:

Gender differences - I was interested to note that resistance exercise has been shown to elevate the concentrations of growth hormone through 30 minutes post-exercise similarly in men and women, although the resting concentrations of growth hormone are significantly higher in women.

Factors affecting the growth hormone response - the magnitude of the growth hormone appears dependent upon the following factors:

• Exercise selection
• Amount of muscle mass recruited
• Muscle actions used (i.e. greater response during concentric than eccentric)
• Intensity
• Volume
• Rest intervals between sets
• Total work performed (multiple-set protocols have elicited greater responses than single-set protocols

In summary, it appears that the growth hormone response to resistance exercise is mainly influenced by the work done in a period of time.  More work in less time produces more growth hormone.  It is not quite as simple as saying “short rest periods”, however, as the total work done is also important.

Strength routines don’t maximise growth hormone – the review article notes that in general, moderate-to-high-intensity, high-volume programmes using short rest periods have shown the greatest growth hormone response compared with strength or power training using high loads, low repetitions and long rest intervals in men.

However, all is not lost, as in the study A single set of low intensity resistance exercise immediately following high intensity resistance exercise stimulates growth hormone secretion in men, by Goto, Sato, Takamatsu, in Journal of Sports Medicine and Physical Fitness, 2003, the researchers looked at a strength protocol (five sets using 90% of 1RM with 3-minute rest intervals) and reported a low growth hormone response.

The researchers discovered that the addition of a single set of high repetitions with 50% of 1RM to the end of the strength protocol elicited a much higher growth hormone response. This suggests that the hormonal response to a strength protocol may be maximised by inclusion of high volume set at the end of the workout.

Resting levels of growth hormone – it appears that resting levels of growth hormone are not affected by resistance training. 

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Cortisol: an introduction

Here’s a brief reminder of what cortisol is and what it does, although if you’ve been reading my blog a while, you’ll already know all about it…

Cortisol (source: Wikipedia) is another steroid hormone, more specifically a glucocorticoid, produced by the adrenal glands.  It is released in response to stress and a low level of blood glucocorticoids.  Its primary functions are to increase blood sugar through gluconeogenesis, to suppress the immune system, and to aid in fat, protein and carbohydrate metabolism.

More specifically for our purposes, glucocorticoids are released from the adrenal cortex in response to the stress of exercise. Of these, cortisol accounts for approximately 95% of the hormonal release.

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Cortisol: the review article

And here is what I found out reading the review article:

Resistance exercise causes increases in cortisol - several studies have shown significant elevations in both cortisol and adrenocorticotropic hormone (the pituitary hormone that stimulates cortisol release from the adrenal cortex) during resistance exercise for both men and women.

What causes the greatest cortisol increases? - unfortunately, the programmes that elicit the greatest cortisol response are those that also elicit the greatest growth hormone response.  Interestingly, the review article notes that some strength protocols failed to elicit a cortisol response whereas hypertrophy and endurance protocols performed by the same subjects elicited more substantial acute elevations through 30 minutes post-exercise.

Carbohydrates limit the cortisol response - the effect of carbohydrate supplementation on the cortisol response to resistance exercise has been studied and some studies suggest that supplementing with carbohydrates after exercise does reduce the cortisol response after resistance training.  However, this is not seen in every study.

Resting levels of cortisol - it appears that resting levels of cortisol are not affected by resistance traing unless the subjects are overtraining significantly.

Combined resistance and endurance training raises cortisol - several studies have indicated that there is an incompatibility between simultaneous high-intensity strength and endurance training.

In the study, Effect of concurrent strength and endurance training on skeletal muscle properties and hormone concentrations in humans, Bell, Syrotuik, Martin, et al, in European Journal of Applied Physiology, 2000, greater urinary cortisol was observed in women who were performing combined strength and endurance training than just strength training.

Similarly, in the study Compatibility of high-intensity strength and endurance training on hormonal and skeletal muscle adaptations, by Kraemer, Patton, Gordon, et al, Journal of Applied Physiology, 1995, the researchers found that subjects performing a total-body, high-volume resistance training programme 4 days per week along with 4 days per week of endurance training for 12 weeks reported a substantial increase in exercise-induced cortisol concentrations as a result of combining resistance and endurance training.

The testosterone / cortisol ratio – this ratio has been suggested to be an indicator of the anabolic/catabolic status of skeletal muscle during resistance training. although the review article notes that the research is not conclusive.  Periodised, higher-volume programmes do seem to produce a significantly greater increase in the ratio than a low-volume, single-set programme, however.

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Insulin-like growth factors (IGFs)

Insulin-like growth factors (source: Wikipedia) are proteins that show high similarity to insulin.  IGFs are part of a complex system (often referred to as the IGF axis) that cells use to communicate with their environment.  IGFs are structurally related to insulin and mediate many of the actions of growth hormone.  They increase protein synthesis during resistance training and enhance muscle hypertrophy.

Response to exercise is unclear - the review article notes that the response of IGFs to resistance exercise remains unclear.  It notes that most studies have shown no change in IGF during or immediately following an acute bout of resistance exercise but that a few studies have shown some elevations both during and following resistance exercise.

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Insulin

Insulin (source: Wikipedia) is a hormone central to regulating carbohydrate and fat metabolism in the body.  Insulin causes cells in the liver,muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle.  Insulin is also used as a control signal to other body systems (e.g. it directs amino acid uptake by body cells) and it has several other anabolic effects throughout the body.

Protein synthesis - the review article notes that insulin has been shown to significantly affect muscle protein synthesis when adequate amino acid concentrations are available, especially by reducing protein catabolism.

Insulin affected by nutrition – the review article notes that insulin concentrations parallel changes in blood glucose, and that this response is enhanced when protein/carbohydrates are ingested prior to, during, or following the workout.

Without supplementation, insulin concentrations decrease during a bout of resistance exercise.  Ingestion of carbohydrates, amino acids, or combinations of both prior to, during, and/or immediately after the resistance exercise protocol is recommended for maximising insulin’s effects on tissue anabolism.

So it would make sense to take carbohydrate with your protein after a workout if you are looking for maximum protein synthesis.

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Catecholamines

Catecholamines (source: Wikipedia) include dopamine, as well as the ”fight-or-flight” hormones adrenaline (epinephrine) and noradrenaline (norepinephrine) released by the adrenal medulla of the adrenal glands in response to stress.  They are derived from the amino acid tyrosine.  Catecholamines are water-soluble and are 50% bound to plasma proteins, so they circulate in the bloodstream.

Resistance exercise inceases catecholamines – the review article notes that resistance training has been shown to increase plasma concentrations of epinephrine, nore-pinephrine and dopamine.

Factors affecting the catecholamine response – the size of the catecholamine response to resistance training appears to be dependent upon the folllowing factors:

• Force of muscle contraction
• Amount of muscle stimulated
• Volume of resistance exercise
• Rest intervals

Anticipatory rise in catecholamines – the review article notes that prior to intense exercise, a significant elevation in plasma epinephrine and norepinephrine has been observed.  This anticipatory rise may be part of the body’s psychophysiological adjustment for preparing to perform during resistance exercise.

I find this last point very interesting.  In my last series on stress, I concluded from reading a number of books about stress and research articles on stress, that arousal is actually key to reducing stress.  And in my concluding article on how to reduce stress, I noted as one of my key points that a lack of excitement causes HPA-axis disruption (which is indicative of chronic stress).

Why did I conclude this?  Well in one of the studies that I reviewed in detail (Arousal and Physiological Toughness) the researcher found that exposing subjects to intermittent stressors leads to strong and sympathetic nervous system adrenal-medullary arousal and suppression of HPA responses.  In other words, getting an adrenaline fix and recovering from it leads to lower cortisol levels.

So, yet another reason for people living stressful lives to do resistance training…

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Concluding remarks

I know that the above information probably flew at you thick and fast, so let me summarise a couple of the really interesting points:

Most hormones – the beneficial effects of most hormones seem to kick in with long-term, high-volume, high-intensity strength training routines, preferably with lower rest periods

Testosterone – there doesn’t appear to be much point in trying to maximise testosterone if you are female.  Men should think hard before performing isolation exercises independently from compound movements and even harder before removing fat from their diets.

Growth hormone – growth hormone is strongly affected by total work and by shorter rest periods.  However, similar benefits can be obtained by using a single set of higher reps at the end of a low-rep, high-rest training session.

Cortisol – the cortisol response to resistance training seems to follow the growth hormone response but it can be reduced by carbohydrate supplementation.

Insulin - insulin stuffs cells full of nutrients and is most affected by carbohydrates, so it seems to make sense to take carbohydrates with your protein if you are looking for maxmium protein synthesis (and therefore hypertrophy).

Personally, my own training and nutritional regimen incorporates many of these points.  For example, I already do quite a bit of volume at high intensities, I only ever do a small amount of isolation work after compound movements, I already eat a lot of fat, and I eat carbohydrate with protein after a workout.

However, I don’t currently maximise my growth hormone response to training by using a set of higher reps after my strength training work.  I will consider this going forwards, even though I really hate high-rep training…