Figure 2.

(a) Old subjects. (b) Young subjects. (a(i),b(i)) The mass-specific vertical stiffness, which is similar in old and young subjects. (a(ii),b(ii)) Shows that the step frequency (f, continuous line) is greater in the old than in the young subjects. In addition, over most of the speed range, the step frequency is similar to the natural frequency of the system (f_s, dashed line) in the old subjects, whereas it is less than the frequency of the system in the young subjects. Statistics and other indications are the same as in figure 1.