Stretching is a great way to complement exercise and improve flexibility, but until now the way exercises like yoga contribute to long-term flexibility has been a mystery.

In a study published today in the online journal Cell, researchers from Columbia University demonstrated how one of the largest proteins in the human body, titin, contributes to muscle elasticity.

Titin is shaped like a coil of rope, and during stretching, that rope is uncoiled to reveal cysteine residues. These hotspots become oxidized during exercise, which stops the titin molecules from re-coiling, leaving them in a more stretched-out state.

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Changing the Elasticity of Muscles

This characteristic of titin may help explain how prolonged stretching activities like yoga contribute to overall flexibility. “The most profound surprise was that muscles don’t just adapt immediately to their surroundings. If you stretch your muscle it becomes softer over time,” said study co-author Pallav Kosuri, Ph.D., now a postdoctoral research fellow at Harvard University.

To observe the uncoiling and oxidation of titin, researchers used highly sensitive light microscopes to detect the chemical reactions in previously froxen human donor heart tissue. They saw that when titin was uncoiled, more hotspots were exposed to oxidation, and that once oxidized, titin remained uncoiled for a period of time.

Strength training and aerobic exercise tend to break down muscles. The idea is that when the muscles build themselves back up, they are stronger. Stretching lengthens muscles by pulling them apart. “What we found was there was a sort of intermediate stage that didn’t require breaking down or building up tissue. You can change the elasticity of muscles and the length of muscle over a time scale of minutes to days to maybe even longer,” Kosuri said.

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How Titin Affects Your Exercise Routine

How strong or fit a person is contributes to how easily he or she is able to exercise. But passive elasticity—the relative flexibility of muscles that does not require active work—could be another factor that contributes to greater athletic performance in some people.

“One of the most fundamental pieces is that a lot of what the muscle does is not just to contract. It’s to use this molecular intrinsic springiness,” Kosuri said. Energy that is generated during a run, for example, mostly goes toward lifting the body up and down off of the ground. “That is actually just elastic energy, [or] energy that is recovered and is used to push you off the ground,” he added. So higher performance is dependent not only on muscle strength, but also on how good the body is at conserving energy.

Titin contributes to the passive elasticity of muscles, making it easier for them to conserve energy. “It’s basically tuning the springiness of your muscles,” Kosuri said. Prolonged stretching, which might occur in a 60- or 90-minute yoga class, leaves muscles relaxed because titin has been uncoiled and oxidized. “The perfect context to use this knowledge is in yoga, where the more oxidation there is, the more activity, the more oxidative compounds are released,” he added.

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Although further study is needed outside of the lab, these findings could potentially change how athletes and regular exercisers consider stretching as part of their workout routine. “[Stretching] does increase the amount of stress that a muscle can tolerate without becoming injured in the isolation of the lab,” Kosuri said. “Whether that scales to a human being needs to be further investigated.”

Beyond exercise and wellness implications, further research on titin could also contribute to new treatments in the field of cardiology. “There are many cardiac disorders where the mechanical properties of the heart are visibly changed. Now we have a molecular mechanism where we can alter heart elasticity,” Kosuri said.

In the future, it’s possible that doctors will be able to manipulate the oxidation level in your heart muscle to bring it within a healthy range. For now, child's pose will have to do.

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