How fast can you build muscle and strengthen tendons?


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There’s an interesting study in the latest issue of the Journal of Strength and Conditioning Research about how quickly your muscles and tendons adapt to exercise — and un-adapt when you stop exercising. (Thanks to Steve Magness for pointing this study out.)

The set-up: 8 subjects did three months of strength training (knee extensions), four days a week, and then stopped training for three months. Once a month, researchers from three Tokyo universities measured changes in the affected muscles and tendons, using high-voltage electrical stimulation, ultrasound, MRI and other techniques.

The results: The subjects were significantly stronger after two months, mostly because of better neural activation. The muscles didn’t get bigger until after three months. The tendons also didn’t get significantly stiffer until after three months.

When the subjects stopped training, the pattern was reversed. After just one month, muscle size dropped back to pre-study levels, while strength stayed significantly higher even three months later. Tendon stiffness dropped to pre-exercise levels after two months.

So what does this tell us? First of all, you need to start pumping iron at least three months before you hit the beach. But more generally, it confirms that tendons adapt more slowly to training than muscles (and then lose training more quickly than muscles). This, the authors hypothesize, is because tendons have slower metabolism — as mediated by blood flow and oxygenation — than muscles.

From a practical point of view, this tells us that there’s a period of mismatch after starting a new training program, where the muscles have adapted but the tendons haven’t yet caught up. This creates a risk of, for instance, Achilles tendon ruptures. The solution? Be cautious. Maybe start that weights program four months before beach season, so you don’t have to push it quite as hard.

One Reply to “How fast can you build muscle and strengthen tendons?”

  1. Here is an anecdote that may interest you. It comes from Christopher McGowan’s popular-science book “Dinosaurs, Spitfires and Sea Dragons” (a book I highly recommend, by the way. McGowan held positions at the ROM and the U of T at the time the book was written.) In the preamble he discusses the mechanical properties of bone, and claims that “the response to changing stress takes days rather than weeks and can actually be measured.” I don’t know the basis for this claim, but he mentions a student who “… sportingly allowed [McGowan] to measure his clavicle both before and after he took up weight training. Over the period of the Christmas vacation his clavicle increase in diameter by three-sixteenths of an inch (4.6mm), an increase of about 25 percent.”

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