2. Test the hypothesis, separately for each elderly group, controlling for co-factors, that there is greater change in step length in the treatment group compared to the control group, after controlling for co-variates. We also expect greater changes in dynamic hip peak extension, a reduction in anterior pelvic tilt, improvement in age-related reductions in peak ankle plantar flexion and ankle power generation, and in dynamic CoM-CoP moment arm during both comfortable and fast walking, and an increase in comfortable walking speed.