Human and animal movements are often more efficient than expected due to energy-saving mechanisms in muscles and tendons. This project aims to determine how tendons affect the physiology (energy use) and biomechanics (strength) of muscles. The tail muscles of rattlesnakes are good muscles for understanding energy-saving mechanisms because they can sustain extremely high levels of exercise without becoming fatigued, and they show very clear relationships among anatomy, mechanics, and physiology. Similarly, the muscle-tendon networks along the snake spine are a good model because their complex interactions via tendons actively modulate force and work. One set of experiments will use the tail shaker muscles of rattlesnakes to test the hypothesis that muscles lacking tendons use significantly more energy than muscles that have long tendons. Similar predictions have been made for locomotion in humans and other animals, but cannot be tested in their muscles because the presence of diverse muscle fiber types makes it difficult to sort out the effects of tendon anatomy from those of muscle physiology (fiber type). This problem is circumvented by studying the muscles in snake tails, because all of the muscles have the same fiber type. A second set of experiments using muscles along the spine of the snake will test the hypothesis that muscular interconnections via long tendons enable the muscles to generate higher forces and use less energy than do muscles with short or no tendons. These results will help explain how muscle-tendon interactions actively modulate force output and energy use. Overall, this work will be important for understanding: (1) the factors that limit or enhance exercise performance in humans and other animals, (2) how complex and poorly understood muscle-tendon systems work, such as those in the human hand, and (3) how to design flexible robots and control their movements, for use in automation, search-and-rescue operations, and other applications. This work will also enhance mentorship and scientific training of students from underrepresented groups.
