The Hormone Hypothesis And Hypertrophy

Acute Hormone Responses And Hypertrophy?

Let’s start off with the obvious: resistance training induces muscular hypertrophy (an increase in muscle size) over time. Pretty standard stuff! Resistance training provides the necessary stimuli which stress the muscle, and following training, the muscle will repair itself and come back stronger and bigger.

However, there is another interesting change that occurs following a resistance training session: the presence of acute hormonal spikes (or post-exercise hormonal elevation, either is interchangeable!). Particularly, testosterone (TS), growth hormone (GH) and insulin-like growth factors (IGF). This is interesting because it has been suggested that these post-exercise hormonal elevations might play an important role in mediating increases in muscle size. Even though it’s well understood how post-exercise hypertrophic adaptations are mediated (through complex enzyme activity in the muscle cell), very little is known about the role these acute hormonal responses play in regulating this hypertrophic response in muscle cells.

What we know:

Resistance training can induce acute changes in several anabolic related hormones such as testosterone, growth factor and insulin-like growth factor. 

What we don’t know:

The role of this acute hormonal spike following resistance training in mediating hypertrophic responses

What has been suggested:

These acute hormonal spikes following resistance training may play an important role in enhancing the hypertrophic responses in muscle cells. 

So what does the science tell us up to now?


Enter The Hormone Hypothesis

In a study published by Kraemer and Ratamess 2005, it was found that high-volume resistance training protocols at moderate intensities (~ 60 to 80% 1RM) and short-rest intervals between sets (~ 60 to 90 seconds), produced the greatest elevations in acute hormone responses (GH, Cortisol and TS), compared with high-intensity, low-volume protocols. 

So, what was deduced from the studies by Kraemer and Ratamess? Well, given 1) high-volume training is generally accepted as the means of mediating muscular hypertrophy, and 2) acute elevations in GH, Cortisol and TS following high-volume, hypertrophy-type training were greatest, it was suggested that these acute hormonal spikes play a critical role in mediating muscle size (Schoenfeld 2013).

Out of these observations, led to the proposal of the the hormone hypothesis. Simply put, the hormone hypothesis puts forward the idea that these acute hormonal spikes following high-volume resistance training methods, play an important role in mediating hypertrophic responses in muscle cells. 

However, there is something important to note: West et al, 2010 conducted a study in young untrained men who performed resistance training in either low basal hormone concentrations [(LH) (achieved through performing only an isolated arm curl exercise)] or high basal hormone concentrations [(achieved through performing first an isolated arm curl exercise, then a high volume leg resistance exercise to elicit a large increase in endogenous hormones (HH)].

Interestingly, West et al found that there were no significant changes in muscle cross-sectional areas in the trained arm muscles between the LH and HH group. This highlighted that hypertrophy occurs to a similar extents in both the LH (without the acute hormonal spike) and HH groups. This suggested that acute hormonal spikes post-exercise might not have an enhancing effect on hypertrophic responses in the muscle cell. 

The bottom line from these studies: The hormone hypothesis tries to branch a link between these acute hormonal spikes and the hypertrophic responses in muscle cells. At the moment it’s not clear what the nature of this ‘link’ is. A prevailing theory is that higher concentrations of hormones post-resistance training are more likely to come into contact with their ‘receptors’, which in turn mediate a cascade of downstream events that act to enhance hypertrophic signalling processes in the muscle cell. But that is just a theory at this point! 

The Evidence For A Hormone Hypothesis? 

Study 1

Hansen et al, 2001 published a study which compared the strength of the elbow flexors in 16 young untrained males after 9 weeks of resistance training. One group carried out arm training only (A), while the second group carried out leg + arm training (LA). Each group trained the same arm (the other acted as a control). 8 sets of standing and seated bicep curls performed for 8-12 repetitions, with rest intervals of 90 seconds). 

The results? After 9 weeks it was found that the strength increases in the trained arm, exhibited by the LA group were ~ 37% in comparison to the A group (~ 9 %). Furthermore, these increases coincided with significant increases in post-training hormonal responses of GH and T in the LA group in comparison with the A group.   

Important point to note: Caution has to be taken when interpreting these results due to the fact that the initial starting strength levels in the LA group were ~ 20-25% LESS than those in A group. Moreover, there was no measure of muscle mass changes (just strength), thus it’s impossible to know if the strength differences were due to increases in hypertrophy or simply through neural mechanisms. 

The conclusion? These results MIGHT support the role for POST-exercise hormonal elevations on hypertrophic responses in muscle cells, but due to experimental limitations, any link remains speculative at best. 

Study 2

Madarame et al, 2008 published a study which looked at the effect of post-exercise elevations in hormones on muscle morphology. In this study, 15 young untrained men were split into two groups: normal training group (NOR) or an occlusion group (OCC). Occlusion is basically restricted blood flow to the target muscle. Blood restriction has been shown to evoke strong hormonal responses. The resistance training protocol consisted of both groups performing 3 sets of dumbbell curls at 10 repetitions per set, at 50% 1RM, with rest intervals of 3 minutes between sets. 

The results? At the end of 10 weeks of training, the OCC group demonstrated greater increases in the cross sectional area of the upper arm in comparison to the NOR group. However, there were no significant differences in the post-exercise elevations of GH and T between the NOR and OCC groups. 

The conclusions? Since the authors highlighted that there were large variations between individuals in the group and the sample size was small, it’s impossible to establish a link between post-exercise hormone elevations and hypertrophic responses. 

Study 3

In another study by Ronnestad et al, 2011, 11 untrained men underwent 11 weeks of resistance training. They were split into two groups: one under low basal concentrations hormone (LL) and one under high basal hormone concentrations (HL). This study is very similar to the study conducted by West et al, 2010 except in this study, the high-volume leg exercise is performed before the arm exercise. 

The results? In contrast to the results published by West et al, Ronnestad et al actually found significantly greater increases in muscle cross sectional area of the arms in the HL group in comparison with the LL group. 

The conclusions? These results suggested that post-exercise hormone elevations are indeed responsible for the greater hypertrophic gains in the HL group. 

Some things worth mentioning:

In this study, compared with that of West et al, higher training volumes were used by participants (6 sets for arms vs. 3/4 sets for arms). It’s likely then that higher training volumes in this study resulted in more muscle micro trauma which could have served to magnify the post-exercise hormone elevations.

This could explain the significant increases in cross sectional areas of the arm muscles in the HL group. It might have been the case that more volume was needed in the West et al study to truly find out the effects of post-exercise hormone elevations on hypertrophic responses.

Although there needs to be more research done to substantiate the link between higher post-exercise hormone elevations in response to more training volume. 

The Verdict?

At the moment, the data is pretty mixed. It’s simply impossible at this stage in the research, to establish a clear link between post-exercise hormonal elevations and hypertrophic responses. Given the limitations and inconsistencies presented in the studies, it would not be wise at this point to draw definitive conclusions!

However, Schoenfeld 2013 highlighted an interesting point in which he suggested that the primary effect of post-exercise hormonal elevations is to increase satellite cell activity* (long-term effect) rather than to increase muscle protein synthesis (short-term effect). If this were the case, then post-exercise hormonal elevations would certainly favour long-term increases in hypertrophy without influencing the short-term gains (changes in muscle protein synthesis). Perhaps if the studies were of longer duration than those above, we might get a better look into the true role of post-exercise hormonal elevations on hypertrophy in the longer term. Although Schoenfeld pointed out that more needs to be done to substantiate this. 

Furthermore, Schoenfeld pointed out that the increases in muscle size in response to post-exercise hormonal elevations are modest (~ 8% as an upper figure). If this is the case, then any effects of post-exercise hormone elevations on hypertrophy are likely to be small in reality. However, for elderly individuals with muscle loss or athletes, a small difference in hypertrophy might make the world of difference in terms of performance and mobility. 

Lastly, the lack of data using trained individuals presents a major drawback to the current research. As schoenfeld 2013 points out, studies have shown that these post-exercise hormonal elevations can be more pronounced in strength athletes compared to endurance athletes or sedentary individuals. This suggests then that post-exercise hormonal elevations might only become significant in hypertrophic adaptations, when individuals gain more resistance training experience. But it still needs to be further investigated! 

*satellite cells are just those cells that DIFFERENTIATE into MUSCLE CELLS. 


The hormone hypothesis is certainly an interesting theory in trying to link the influence of post-exercise hormonal elevations to hypertrophic responses in the muscle cell. While the data is inconclusive at the moment, I do believe that these post-exercise elevations serve a purpose. Given that GH, T and IGF have all been implicated in anabolic processes, it’s highly likely that post-exercise hormonal spikes serve an important role in regulating hypertrophy. To what extent, we don’t know at present. 

Further research?

To establish the ‘nature of the link’ between post-exercise hormonal elevations and hypertrophic responses. Are post-exercise hormonal elevations necessary, or do they merely have a ‘supportive role’ in hypertrophy? 

The relationship between increasing training volumes and the extent of these POST-exercise hormonal spikes

If post-exercise hormonal elevations do play an important role in hypertrophy, how can we best manipulate training variables to ensure optimal post-exercise hormonal elevations so that we can maximise hypertrophic responses. 

Any questions, ask away!


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