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22.10.2010

Myostatin blockers reduce stamina

The myostatin blockers that chemical strength athletes are pinning so many hopes on probably have a negative effect on endurance capacity. This is the conclusion from an animal study done under Alexandra McPherron, who has done pioneering research on myostatin and has half a dozen patents to her name. [faqs.org]

The illustration here shows the spatial structure of the protein myostatin. Muscle cells make myostatin to limit their own growth. Pharmacists are working on muscle-strengthening medicines that block this protein in the search for ways to help people with muscular dystrophy or sarcopenia. [Business Wire May 14 2007] [Offline] Photos of frighteningly muscled animals that can't make myostatin, whether through a mutation or genetic modification, are icons in the bodybuilding world – they are as well known as photos of Gregg Valentino’s monster-sized arms.

McPherron and her colleague, Kathleen Savage, published an article in Muscle Nerve reporting on an experiment they did with mice like the ones you've seen in photos.

Myostatin blockers make muscles bigger. They are becoming popular in bodybuilding circles, and if they also increase strength, they'll also become popular in strength sports like power lifting and weight lifting. But what do these substances do to the ability of muscles to keep functioning for extended periods of time? What do they do to stamina?

To answer this question the researchers trained ordinary mice [Mstn +/+] and mice that had been modified so that they couldn't manufacture myostatin [Mstn -/-]. For a period of four weeks, the mice ran five times a week for half an hour in a treadmill.

At the end of the training period the super-muscled mice had lost out to the mice with intact myostatin genes. The myostatin-less mice did make progress with the training, but not as much as the ordinary mice. In a test where the animals had to run at an increasing speed, the muscled mice ran 28 percent less long and covered 40 percent fewer metres than their counterparts. Their endurance capacity was 38 percent less than that of the ordinary mice.

The figure below shows the increase in lean mass in the test subjects. The dark bars represent the lean mass in the arms and legs. The lower figure shows the amount of fat that the subjects lost. The dark bars represent fat mass in the trunk. The results confirm what bodybuilders know already: growth hormone and testosterone reinforce each other's effects.

Deactivating myostatin leads to an increase in the number of 'fast' muscle fibres that generate short-term power, but reduces the number of oxidative muscle fibres that are capable of functioning over a longer period.

The conversion of nutrients into energy takes place via the citric acid cycle. In the first step of the cycle involves the enzyme citrate synthase. The figure above shows that the activity of this enzyme in the triceps, the quadriceps (Quad), the plantaris (Plt) and the gastrocnemius (Gas) is lower in the myostatin-less mice.

Perhaps this study answers the question as to why humans make myostatin at all. After all, if it weren't for this protein getting in the way, we'd all be superhumans with massive muscles. Probably it's been more important for our species to be able to run away fast than to be strong.

Source:
Muscle Nerve. 2010 Sep; 42(3): 355-62.

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Myostatin blockers destroy tendons 06.10.2008

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