For this pilot study the investigators will enroll 20 sedentary older adults at risk for disability (usual gait speed ≤ 1.0 m/s). Participants will be assigned to one of two 12-week interventions. Therefore the final training pool will consist of 10 split-belt participants and 10 traditional treadmill participants. Aim 1 will test the hypothesis that compared with a traditional treadmill intervention a split-belt treadmill intervention will result in improved mobility, as measure by 400 meter walk time, as well self reported physical function/disability as measured by the Pepper Assessment Tool for Disability. Aim 2 will test the hypothesis that compared with a traditional treadmill intervention a split-belt treadmill intervention will results in improved gait variability. To date, no experimental study has evaluated these propositions in a controlled trial testing the effects of split-belt training in older adults at risk for disability.