The influence of instruction on arm reactions in individuals with Parkinson's disease

The purpose of this study was to examine whether explicit instruction would facilitate arm reactions in individuals with Parkinson's disease (PD). Individuals with (n = 10) and without (n = 15) PD responded to unexpected support-surface translations. To recover their balance, participants were required to either respond naturally (react natural) or to reach toward a nearby handrail (explicit instruction). Arm reactions were quantified from electromyographic (EMG) and arm kinematic recordings. Results showed that while explicit instruction led to earlier and larger arm reactions, the benefits were not different between individuals with and without PD. Specifically, when explicitly instructed to reach toward a handrail, shoulder EMG responses were 4% earlier (p = .005) and 32% larger (p < .001) compared to when instructed to react naturally. A 44% greater peak wrist medio-lateral velocity (p < .001) and a 29% greater peak shoulder abduction angular velocity (p < .001) were also observed when participants were instructed to direct their arms toward a handrail after an unexpected support-surface translation. Explicit instruction also led to a higher frequency of handrail contact and a 49 ms earlier time to handrail contact compared to the react natural condition (p = .015). These results suggest that providing instruction to promote arm movement may help reduce falls in older adults with and without PD.