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Myostatin blockers destroy tendons

Myostatin blockers, the new group of muscle strengtheners that chemical athletes are waiting for with baited breath, have a serious side effect. Researchers at the University of Michigan discovered this while doing experiments with mice that had been genetically modified so that they could no longer produce myostatin. The muscles of the mice were bigger and stronger, but their tendons were small and brittle.

Myostatin is a protein that muscles produce if they are over-trained or if they become weaker as a result of ageing (frailty). The only function of myostatin that researchers have found so far in adult organisms is that it retards muscle growth. This is why the pharmaceutical industry is experimenting so avidly with myostatin blockers, in the hope that they can help to keep people with muscle disease or age-related frailty healthy for longer. Wyeth Pharmaceuticals is already at an advanced stage in the process of developing a human myostatin blocker.

The expectation is that myostatin blockers will turn up sooner or later in the sports world if they are not already there.

The news from Michigan is certainly interesting for sports users. The researchers compared mice with functioning myostatin genes (MSTN +/+) with mice whose myostatin genes had been destroyed (MSTN -/-). The table below shows you the mass of the tibialis anterior muscle in the two groups of mice, and the mass of the tendon.

Myostatin blockers destroy tendons

The researchers found myostatin receptors in the tendons. When they looked at the strength of the tendons of the normal mice and those without myostatin, the researchers also noticed that the tendons of the mice without myostatin were more brittle and stiff. You can see the stiffness in the graph below.

Myostatin blockers destroy tendons

"Those interested in myostatin inhibitors need to be aware of the fact that by doing these things to muscles, they may be having negative effects on tendons", warns research leader John Faulkner. The researchers suspect that muscles manufacture myostatin for a reason: it appears to strengthen the tendons.

The research, which was published in the prestigious PNAS, is bad news for the outer frontier in the chemical sports world. But it's interesting for sports scientists who are seeking ways to make damaged joints healthy again. Perhaps training schedules that are tailored to produce an optimal amount of myostatin will be the solution. A sort of adjusted over-training, you could say.

Proc Natl Acad Sci U S A. 2008 Jan 8;105(1):388-93.