Regular exercise for the Parkinson's sufferer will reduce the incidence of muscle cramps, rigidity of the joints and the aches and pains associated with staying still for long periods of time. Also, because exercise helps the sufferer to maintain control over many of their gross movements (although maybe not the tremors) it gives them a heightened sense of achievement and so stress and anxiety levels remain low. Keeping a positive mental attitude is incredibly important in conditions like Parkinson's disease where sufferer can very easily become frustrated and discouraged with their predicament.
Following a stroke you should know that exercise is very important for stroke recovery and for preventing another stroke. Only slightly more than half (57%) of stroke survivors are getting regular exercise, according to a survey of 11,862 men and women who had survived at least one stroke.