Push-Off Efficacy in Parkinson's Disease compared to healthy controls and its relationship with step length

The reduction of step length is one of the most common gait impairments in patients with Parkinson's Disease (PD). However, the neuromuscular strategies associated to this gait impairment are still unclear. This study aimed to investigate the potential relationship between muscle activation and step length in PD and healthy controls. In this observational study, we employed a linear regression model to quantify the relationship between step length and gastrocnemius medialis activation in PD and in healthy controls (HC). Muscle activity was quantified using the area under the curve (AUC) of the EMG envelopes during the push-off phase of the gait cycle, normalized to peak of activation across trials. Comparisons of time-varying EMG activation profiles and of step length between PD and HC were performed to identify potentially different neuromuscular strategies between the two groups. A reduction of step length (mean difference [MD] = 6.22 cm; 95 % Confidence Interval [CI]: 1.05;11.40; p = 0.021), even when normalized to subject height (MD = 3.16 %; 95 %CI: 0.39;5.92; p = 0.027), was found. A modest to high correlation between step length and gastrocnemius medialis activity was found only in HC (r = 0.623; p = 0.007), while there was no correlation between these two variables in PD (r = 0.214; p = 0.294). In PD the reduction of step length is therefore not associated with gastrocnemius medialis activity during push-off. Therefore, different mechanisms may underpin this behavior and are discussed.