The purpose of this study was to compare the moment-angle relationship of the ankle joint during running and sprinting to determine how the dynamic angular stiffness is influenced by different activities. For both running and sprinting, the results indicated that the ankle joint produced an exclusively extensor moment, absorbing energy during the first half of the stance phase and producing energy during the second half. The biphasic nature of the joint absorbing energy followed by the joint producing energy, while continually creating an extensor moment, was similar to a spring being compressed and allowed to extend. The dynamic stiffness of the ankle joint was 5.68 N · m/° for running and 7.38 N · m/° for sprinting. It appeared that the stiffness of the ankle joint was not a specialized characteristic of each individual but rather a specialized characteristic of the activity or demand placed upon it.
The authors are with the Human Performance Laboratory, The University of Calgary, Calgary, Alberta T2N 1N4 Canada.