Swimming: Forces on Aquatic Animals and Humans

The biomechanics of locomotion is a diverse and interesting field involving several aspects of physics and various approaches to mathematical modeling. The study of swimming, however, presents problems which are quite different from those encountered in the analysis of movement on land. Except for creatures without legs, the analysis of locomotion in land animals is essentially similar, whether one is considering a flea, a horse, or a man. One makes assumptions about ground reactions and body segments and develops equations of motion which relate the observed movement patterns to muscle forces. In the case of movement through water, however, the mechanisms and conditions of locomotion become more diverse, and swimming research has proven to be extremely uneven in its progress. In some cases, the analysis has been elegantly executed and highly successful. In others, it has been largely descriptive and little understanding of the involved mechanisms has evolved. In part, this irregular progress is attributable to the fact that fluid dynamics is a less precise discipline than rigid body mechanics. On the other hand, the success achieved in analysis has to some extent correlated with the success achieved by the swimmer. Those animals which swim very well have been the subjects of the more elegant mathematical theories; those which splash about rather clumsily have not been easy to analyze. Human swimmers fall into the latter category, and the situation has not been helped by the fact that most university sport sciences curricula do not include advanced courses in fluid mechanics, or even the necessary prerequisites.