The study of split-belt treadmill adaptation provides insight into the priorities determining how we adapt to novel conditions during walking. During split-belt adaptation, young adults reduce their metabolic cost and positive leg work in part by learning to take longer steps on the fast belt, thus adopting a positive step length asymmetry. However, aging may lead to a shift in the work performed by distal versus proximal joints, so it is unknown if older adults can similarly reduce the work performed by the legs during split-belt walking. Therefore, we quantified the relationship between joint work rate and step length asymmetry when fourteen older adults walked on a split-belt treadmill. We hypothesized that total positive joint work would decrease at more positive step length asymmetries and that more positive asymmetries would be associated with a reduction in positive ankle joint work on the fast belt. We found that step length asymmetry was negatively correlated with total positive work (p = 0.01) and that changes in positive joint work were primarily driven by positive ankle work on the fast belt (p = 0.01). Since ankle musculature is hypothesized to be a major contributor to metabolic cost during gait, reductions in ankle joint work likely contribute to the reduction in metabolic cost observed in other studies of split-belt walking. These results demonstrate that healthy aging still allows individuals to take advantage of the work performed by the treadmill to reduce the mechanical energy cost of walking.