Classic gym wisdom states that a strength training session acutely increases the amount of anabolic hormones in the blood, such as testosterone and growth hormone. This creation of an ‘anabolic environment’ is then believed to lead to more long term muscle growth, coined the hormone hypothesis. Based on this idea, many believe that in order to maximally grow one’s biceps, the legs should be trained first. But does science agree with this matter?

How hormones work

Hormones are produced by various organs such as the testicles (testosterone), pancreas (insulin and glucagon) and the pituitary gland (growth hormone). They can be subdivided into amino acid molecules (growth hormone) and fatty molecules (testosterone), which influence cells by binding to specific receptors for that hormone. Not only the amount of a certain hormone present in the blood, but also the number of receptors for that hormone determines what ultimately happens in the cell.

Research into strength training and hormones

Typical bodybuilding training protocols (lots of sets, little rest) are effective at naturally increasing testosterone and growth hormone, and have led to the genesis of the hormone hypothesis. However, we may wonder whether this increase in hormones through strength training is actually required to stimulate muscle building. Over the past decades, quite a lot of research has been done to find out whether the hormone hypothesis is relevant for those with a love for lifting weights. Let's go over it:

Initial studies (1999, 2003) showed strong relationships between the acute increase in growth hormone and testosterone from strength training and growth of our beloved muscles. But more recently (2012), Canadian research showed that there seems to be little relationship between the acute increase in growth hormone and testosterone and the thickening of muscle fibers.

The same Canadian researchers had previously conducted a study in which subjects strength trained for 15 weeks. Subjects trained one arm in a "high hormone condition" (biceps curls 4x8-12, followed by 5x10 reps leg press and 3x12 reps leg extension/leg curl) and the other arm on a separate day in a "low hormone condition" (biceps curls 4x8-12 only). The idea behind performing leg exercises after the biceps curls was that training the big leg muscles would lead to a steeper increase of hormones in the blood (high hormone condition), so the biceps would then grow more. However, despite the "high hormone condition" the researchers did not find any difference in muscle strength and muscle mass between the two groups after 15 weeks of training.

Time to put the hormone hypothesis in the trash, you may think. But in 2011 researchers from Norway came up with a study that had almost the same setup, only the leg exercises were done before the arm exercise. And they actually did measure a greater increase in muscle mass in this case. Their explanation was that a high concentration of hormones in the blood before training a muscle might make it more sensitive to grow from a subsequent workout. However, this was later refuted through Canadian research which concluded that blood-mediated release of hormones to the arms is actually not influenced by the order in which exercises are performed.  

Latest insights

Last October the same group of Canadian researchers published another study to provide more insight into the effect of hormones on muscle growth. In order to do this, they released an extensive statistical analysis on a previously conducted study in 49 strength trained men. They analyzed the data of increases in muscle mass, circulating "anabolic" hormones in the blood and muscles, and the amount of so-called "androgenic" receptors. These receptors, which we discussed earlier, can be seen as 'receivers' on muscle cells on which hormones can act. The most important conclusion of this research was that not the amount of "anabolic" hormones determines how much muscle mass a person builds, but rather the sensitivity of the muscles to hormonal signals. The subjects in this study who showed the greatest increase in muscle mass did not have higher hormonal values, but they just had more receptors in their muscles. The researchers speculated that this may explain why some people build muscle more readily than others.

Weighing the arguments for and against the hormone hypothesis

All that science sounds cool, but what is the takeaway? Based on the Norwegian study there seems to be a (small) chance that the sequence of exercises plays a role in the effect of "anabolic" hormones on muscle growth. However, pending more research, the strongest evidence seems to oppose the hormone hypothesis. Firstly, it is important to realize that the increase in hormones such as growth hormone and testosterone after a strength training session is short (+/-15-60 minutes) and much lower than the extremely high values seen in doping users. A second strong argument against the hormone hypothesis is the gender comparison. Men have 10 to 15 times higher testosterone values at rest, and 45 times higher testosterone values after strength training than women. Despite this, women build muscle protein at similar rates (both at rest and post training) and display similar relative muscle growth after training. And thirdly, there is now a possible explanation for why people build muscle at different rates in response to the natural hormonal increase due to strength training: it seems that the sensitivity of muscles to hormones is the deciding factor.

Conclusion

The available research indicates that the role of increased testosterone and growth hormone in the blood due to strength training is probably very small. However, it is common practice to train large muscle groups before small ones, so should there be an effect: you're probably already reaping its benefits. Also, we know from both practice and research that the order of exercises is better determined by what exercises are needing the most attention, because energy and attention are limited. So, by all means keep your training sessions revolving around big compound movements, but on the premise that its mechanical load and training volume that are causing growth - not the hormonal response.

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