Altered joint kinetic strategies of healthy older adults and individuals with Parkinson's disease to walk at faster speeds.

Individuals with Parkinson's disease (PD) exhibit poorer walking performance compared to healthy, age-matched adults. Lower extremity joint kinetics may provide insight into this performance deficit but are currently lacking in the PD literature, especially across multiple speeds. The primary purpose of this study was to compare joint kinetics between individuals with PD and healthy older adults at both comfortable and maximal walking speeds. Secondarily, we quantified relationships between joint kinetics and walking speeds within each group. Biomechanical gait analyses were conducted for 13 individuals with PD and 12 age-matched controls during comfortable (CWS) and maximal (MWS) speed walking. Relative contributions to total positive work from the hip, knee, and ankle were compared across groups and speeds. Within each group, relationships between relative joint work and CWS and MWS were also quantified. Significant group by speed interactions indicated that healthy older adults increased hip and decreased ankle relative work at MWS compared to CWS whereas relative work at all joints in PD group remained stable across speeds. In the older group, positive relationships were observed between relative hip work and MWS. In the PD group, negative relationships were observed between relative hip work and CWS and MWS. Healthy older adults disproportionately increased mechanical contributions from the hip at MWS compared to CWS. Individuals with PD did not exhibit similar disproportionate scaling of joint kinetics across speed conditions. Inability to appropriately scale joint kinetics in PD may represent an inflexible neuromuscular system in PD, which may limit walking performance in this population.