Damper for bad vibrations.

This research presents the hypothesis and findings that short muscle fibers in horses and other large mammals may protect bones and tendons from damaging vibrations during running, negating the previous belief that these fibers were redundant evolutionary remnants.

Theoretical Background

• The researchers began their study by examining the function of short muscle fibers in the legs of horses and camels. These fibers, attached to tendons of notable length, appear to change only minimally in length during movement, which initially led scientists to believe they were redundant in such large animals.
• The article discusses the importance of tendon elasticity, especially in heavy mammals and birds. Tendon elasticity allows for energy conservation during running by acting like a spring, storing kinetic and gravitational potential energy when the foot hits the ground and releasing it as the foot lifts off the ground again.
• The authors also note that this stored and subsequently released energy allows animals to effectively ‘bounce’ whilst running, using less energy than if their tendons were not elastic.

The New Hypothesis: Dampening Vibrations

• Despite the apparent lack of need for short muscle fibers to change length during movement, the authors ruled out the idea that these fibers are redundant. They hypothesized that instead, these fibers protect the bones and tendons from vibration-related damage.
• When large animals run, each footfall elicits a vibration in the leg at a relatively high frequency. If not properly controlled or dampened, these vibrations could damage the bones and tendons, leading to conditions like stress fractures and tendonitis commonly observed in athletic animals and humans.

Evidence and Suggestions

• Through their studies on horse limbs, the authors discovered that these short muscle fibers act as a damper for the harmful vibrations that occur on foot impact.
• These vibrations are especially important in the context of tendons since tendon damage accumulates both over time and with the number of applications of stress. This differs from bones, which only factor in total stress duration, making tendons more susceptible to vibration-induced damage.
• However, one note of contention by the author lies in the effectiveness of these short fibers in protecting bones. The author expresses skepticism about whether these vibrations would significantly accelerate bone damage.

Muscle Fibers Versus Other Damping Materials

• In considering why these tiny muscles have assumed this vibration-damping role, the authors acknowledge that any viscoelastic material could serve the purpose. Tendons, with their limited elasticity due to their spring-like function, are poor at damping vibrations. They dissipate only about 7% of stored work as heat, which, under excessive frequency, could even damage the tendon due to overheating.

Study Significance

• The authors conclude by emphasizing the significance of the study in uncovering an essential function for what was previously believed to be functionless. The research challenges the notion of redundancy or uselessness in certain biological structures, and asks whether other supposed evolutionary remnants might indeed serve unrecognized purposes.