LLEWELLYN, M.A.*; ROBERTS, T.J.: The Work of Acceleration in Running Dogs

It has been hypothesized that the majority of the work done during rapid accelerations in dogs originates from the pelvic limbs. During steady-speed running, the thoracic and pelvic limbs act like springs, absorbing and releasing work. Early in the step, the limbs perform negative work to decrease the energy of the body. Later in the step, they produce positive work to increase the energy of the body and maintain steady speed locomotion. To accelerate, a running animal must either decrease negative work, increase positive work, or both. We measured the mechanical work produced by the pelvic and thoracic limbs during accelerations in dogs. Domestic dogs enthusiastically accelerated over a force-plate while we recorded high-speed video. From force-plate ergometry, we calculated the mechanical work produced by the thoracic and pelvic limbs during accelerative strides. We found that the pelvic limb contributes approximately 2/3 of the total work, while the thoracic limb contributes the remaining 1/3. In comparison to steady-speed running, acceleration was achieved by increasing positive work and decreasing negative work. During the most rapid accelerations, the dogs were able to avoid any decline in mechanical energy of the body during a stride. This suggests that dogs have the ability to eliminate the spring-like function of their limbs, producing only positive work during accelerations. Our results supports the hypothesis that the pelvic limb contributes the majority of work during rapid accelerations in dogs. In addition, this study offers insights into how muscle function is modified for different locomotor activities. Supported by NIH grant AR46499 and an APS Undergraduate Summer Research Fellowship.