This reminds me of a story from several years ago where, as part of a bike-a-thon to benefit Parkinson's research, a Parkinson's patient rode a tandem bike with a family member providing the pedal power. This "passive exercise" led to a several day remission of Parkinsonian symptoms. The current article would provide a plausible mechanism for this effect.
This is the opposite of news Like saying, increased exercise increases oxygen transport in lungs..
OF COURSE physical activity boosts dopamine transport in the substantia nigra.