Small animals move their limbs at higher frequencies than animals and it costs more energy per gram for a small animal to move a given distance than for than for a large one. The questions we address in the grant is the muscular system designed to permit much more energy for small animals to run than large ones? It has been hypothesized that the underlying mechanisms lies in the properties of the muscle fibers. The fibers of the small animals are thought to have maximum velocity of shortening (Vmax) which enables them to shorten faster and generate force and relax faster- -a necessity for the high frequencies aty which they run. But there is a price: fibers with high V(max's) use far more energy to generate force, thus potentially explaining why it is more costly for small animals to run. With the new techniques that we have developed, we will test the above hypothesis by measuring how V(max) and the energetic cost of generating force of different fiber types scales with body size in mammals ranging from mice to horses.
