Motor Output Variability Impairs Driving Ability in Older Adults.

BACKGROUND The functional declines with aging relate to deficits in motor control and strength. In this study, we determine whether older adults exhibit impaired driving as a consequence of declines in motor control or strength. METHODS Young and older adults performed the following tasks: (i) maximum voluntary contractions of ankle dorsiflexion and plantarflexion; (ii) sinusoidal tracking with isolated ankle dorsiflexion; and (iii) a reactive driving task that required responding to unexpected brake lights of the car ahead. We quantified motor control with ankle force variability, gas position variability, and brake force variability. We quantified reactive driving performance with a combination of gas pedal error, premotor and motor response times, and brake pedal error. RESULTS Reactive driving performance was ~30% more impaired (t = 3.38; p < .01) in older adults compared with young adults. Older adults exhibited greater motor output variability during both isolated ankle dorsiflexion contractions (t = 2.76; p < .05) and reactive driving (gas pedal variability: t = 1.87; p < .03; brake pedal variability: t = 4.55; p < .01). Deficits in reactive driving were strongly correlated to greater motor output variability (R 2 = .48; p < .01) but not strength (p > .05). CONCLUSIONS This study provides novel evidence that age-related declines in motor control but not strength impair reactive driving. These findings have implications on rehabilitation and suggest that interventions should focus on improving motor control to enhance driving-related function in older adults.