mTOR, Muscle Growth and Supplements


In my time off from training, I like to spend a bit of time researching things that I hear little snippets of information here and there about. Driving home from a race once, I was listening to a podcast from Keith Baar, a molecular biologist. The podcast was primarily about mTOR and AMPK, what they do within the body, and how we can maximise their benefits. This got me interested, so I thought I would pull some papers off the internet, and see what else I could find. Suffice to say a lot of the technical details were well over my head, but hopefully I can simplify the basics of the mTOR pathway in this article, and how to get the most out of it.

Firstly, we should probably introduce the star of the show, the aforementioned mTOR pathway. mTOR stands for mammalian target of rapamycin, and it is the pathway through which muscle protein synthesis is activated. During and immediately after resistance training, various target proteins in the mTOR pathway are activated through a series of complex chemical reactions, the end effect of which is an increase of muscle protein synthesis for a period of up to 72 hours post-workout. This is the driving force behind muscular hypertrophy.

A large number of papers on this subject look at nutritional interventions, and their effects on this signalling pathway. In a 2009 paper, Hulmi et al. examined the effect on a whey protein supplement on muscle hypertrophy, with a specific eye on the mTOR signalling pathway. They had three groups- the whey protein group, placebo and control take part in a single resistance-training bout, followed by a further 21-week resistance exercise-training programme. They found that the ingestion of 15g of whey protein before and 15g after a resistance training session significantly increased signalling in the mTOR pathway, as well as prolonging this signalling relative to both placebo and control.

A second study by Dreyer et al. (2007) looked at the effect of an Essential Amino Acid (EAA) and carbohydrate (CHO) containing supplement on protein synthesis post exercise. Again, in this study there was a control group. The main finding from the study was that EAA+CHO ingestion enhanced mTOR signalling and increased muscle protein synthesis post-resistance exercise. There was a 41% increase in muscle protein synthesis in subjects not taking the EAA-CHO supplement, compared to a 145% increase in the supplement group. Possible mechanisms for thee results included that EAAs (and, in particular, Leucine) activate the mTOR pathway, and that activation of this pathway may also be through insulin stimulation (the result of CHO ingestion).

A review article by Blomstrand et al. (2006) looked into the effect of branched-chain amino acids (BCAAs) and their effect on protein synthesis following resistance exercise. They stated that although resistance exercise increased protein synthesis, it also increased protein degradation, and hence protein intake was important in order to provide a net protein gain. They speculated that the use of BCAAs post-exercise might increase protein synthesis via two pathways. The first was that an increase in amino-acid (AA) availability leads to an increase of AA uptake into muscle, which stimulates the rate of protein synthesis. The second theory was that a specific AA, or group of AAs, had a stimulatory effect on protein synthesis.

The final paper I read was one by Norton & Layman (2006) on Leucine and protein synthesis. They stated that Leucine had many important functions within the body, including being a constituent of protein, a regulator of protein synthesis, a modulator of the insulin signal cascade, and a stimulator of mTOR. The most interesting part of the review article was with regard to AMPK, which is activated when energy levels in the cell are low. AMPK appears to inhibit mTOR activity, so resistance training with low glycogen levels, or long, exhausting training sessions, appear to be negative.

So, what are the practical aspects of this? Well, to keep AMPK in check, it might not be a good idea to do heavy cardio work post-weights, or to have excessively long workouts. If you want to mix both, it might be a good idea to do a morning/evening split, with one session in the morning, and the other in evening. From a nutritional standpoint, it seems apparent that some sort of protein-carbohydrate mixture immediately after weight training work out is necessary. For me, I use Myprotein true whey (35g) along with somewhere between 15-30g of a simple carbohydrate, like dextrose. The amount differs according to how hard the session is. I also go one step further and add some Leucine to my protein shakes, as that seems to have special effects on its own, possibly by increasing insulin in a similar fashion to carbohydrates. An alternative to this might be to use MP’s EAA powder or tablets, or maybe even BCAA powder or tablets. Why not give it a go and see if you get any further benefits.

You can listen to Keith Baar’s podcast (if you are from the UK) at:

The articles I referenced are all available for free in full-text format. They are:

Blomstrand, E., Eliasson, J., Karlsson, H. & Kohnke, R. (2006) Branched chain amino acids activate key enzymes in protein synthesis after physical exercise. J Nutr. 136 269S-273S.

Dreyer, H., Drummond, M., Pennings, B., Fuijita, S., Glynn, E., Chinkes, D., Dhanani, S., Volpi, E. & Rasmussen, E. (2007) Leucine-Enriched essential amino acid and carbohydrate ingestion following resistance exercise enhances mTOR signalling and protein synthesis in human muscle. Am J Physiol Endocrinol Metab 294 E392-E400

Hulmi, J., Tannerstedt, J., Selanne, H., Kainulainen, H., Kovanen, V. & Mero, A. (2009) Resistance exercise with whey protein ingestion affects mTOR signalling pathway and myostatin in men. J Appl Physiol 106 1720- 1729.

Norton, N. & Layman, D. (2006) Leucine regulates translation initiation of protein synthesis in skeletal muscle after exercise. J Nutr. 136 533S-537S