PubMed1995
Just as in running, the two-joint muscles acting at the hip and at the knee work to transfer energy efficiently between body segments. This can be seen in Figure 12. The powers at the hip and knee are overlaid to show that when power is generated at the hip, it is absorbed at the knee and vice versa. For example, a concentric contraction of the hamstrings proximally at the hip is coupled with an eccentric contraction at the knee just prior to initial contact in terminal swing. The rectus femoris functions in a similar way but in an opposite direction in initial swing. For the three conditions discussed, the relative contribution of work occurring at each joint is different. Figure 13 shows that the muscles about the ankle are the most important source of work in walking and that the knee musculature does not significantly contribute to the work done for walking. In walking, the knee is felt to be important for the smoothing of gait. The quadriceps are a much more important source of energy at the knee in both running and sprinting, as can be seen in Figure 13. Finally, the hip musculature becomes the dominant source of work in sprinting in our group of untrained subjects with significant contributions from both the hip flexors and extensors. One would expect that the relative importance of each of the muscle groups about each of these joints in terms of sources of energy might change with training. The intent of this work was to evaluate the three conditions of walking, running, and sprinting. I hope that it will stimulate further interest and research in this area in order to come to a greater understanding of human locomotion. As more knowledge and experience are gained, the motion analysis lab will be able to offer insight into training strategies, injury prevention, and the treatment of pathologic running and sprinting conditions.