Most of us omnivores eschew turkey tendons, the elastic strands that get in the way of a forkful of pure dark- or light-meat delight. For a team of Brown University researchers, however, these dinner discards are providing some new insights into how our bodies move and protect important muscle fibers.
High-impact activities, such as hiking down a mountain, can be hard on our muscles, as the hard shock of landings damages fibers (fascicles) during descent.
Muscles, however, are not acting alone, it turns out. "We used to think that all of the motion of the body could be explained from the action of our muscle motors," Thomas Roberts, an associate professor of biology at Brown and co-author of the study, said in a prepared statement. "It is becoming increasingly apparent that springy tendons are a big part of what makes us go." And what help us stop, according to the new turkey research, published online Tuesday in Proceedings of the Royal Society B.
Turkeys happen to have a similar muscle and tendon structure in their legs as humans do, even though their knees bend the opposite way. So the researchers dropped half a dozen wild turkeys (Meleagris gallopavo) and used high-speed sensors and cameras to observe their landings. How do you drop a 9.5-pound turkey, scientifically? The birds were placed in harnesses, lifted 1.5 meters into the air and then released (a height from which, the researchers noted, "the animals were able to land safely, repeatedly in a controlled fashion"). Foil strain gauges glued to turkey's tendons were used to measure changes in muscle fibers 1,000 times a second via sonomicrometry.
The turkey landing data suggested that tendons can protect surrounding muscle fibers by taking in a good portion of the initial energy from a hard landing—then releasing it back to surrounding muscles more slowly.
"Something has to take up the slack, and it falls to the tendon," Nicolai Konow, a postdoctoral research in ecology and evolutionary biology at Brown, and paper co-author, said in a prepared statement.
The process of landing turns out to be similar to what we already know about how the tendons and muscles work together to take off for a jump. When a person—or domestic fowl—jumps up, the power initially generated by the muscle is, in part, stored by the tendon, which provides the quick-release burst of energy. Just the opposite happens upon landing to dissipate the energy, the new findings suggest: "Power attenuation is similar to the familiar mechanisms of power amplification," the research team wrote in their study. "In both cases, the tendon allows a separation in time of the muscular event and the movement event." On the turkeys' landings, the muscle fibers stiffened against the impact, sending energy to the tendon, which then released it some 2.4 times more slowly back to the muscle fibers.
The findings could have an impact, so to speak, on reconstructive tendon surgery as well as sports training, where the results might come as somewhat of a shock. After all, tendons are often thought of as the vulnerable links, owing in part to the major problems they can cause if they snap (think of poor Achilles). But perhaps we can think of the tendons as protectors, too. "We can say that in real ways, the muscle has a safety net with the tendon there protecting it," Konow said.