External work and potential for elastic storage at the limb joints of running dogs

The storage and recovery of elastic strain energy in muscles and tendons in creases the economy of locomotion in running vertebrates. In this investiga tion, we compared the negative and positive external work produced at indiv idual limb joints of running dogs to evaluate which muscle-tendon systems c ontribute to elastic storage and to determine the extent to which the exter nal work of locomotion is produced by muscles that shorten actively rather than by muscles that function as springs, We found that the negative and po sitive external work of the extensor muscles is not allocated equally among the different joints and limbs, During both trotting and galloping, the va st majority of the negative work was produced by the two distal joints, the wrist and ankle. The forelimb produced most of the negative work in both t he trot and the gallop. The hindlimb produced most of the positive work dur ing galloping, but not during trotting. With regards to elastic storage, ou r results indicate that the forelimb of dogs displays a greater potential f or storage and recovery of elastic energy than does the hindlimb, Elastic s torage appears to be more important during trotting than during galloping, and elastic storage appears to be more pronounced in the extensor muscles o f the distal joints than in the extensor muscles of the proximal joints. Fu rthermore, our analysis indicates that a significant portion of the externa l work of locomotion, 26 % during trotting and 56 % during galloping, is pr oduced by actively shortening muscles. We conclude that, although elastic s torage of energy is extremely important to the economy of running gaits, ac tively shortening muscles do make an important contribution to the work of locomotion.