What are Purkinje Cells?
Purkinje Cells Defined: A specific type of nerve cell that carries each and every piece of information outputted by the cerebellum. These cells possess a great deal of control over the refinement of motor activities. Wikipedia offers information on Purkinje Cells.
The Studies: Rats, aged 5 to 23 months, were divided into two groups, one was exercised in a certain manner and the other was left to be sedentary. The first study found that sedentary aged rats had 11% fewer Purkinje cells and 9% smaller Purkinje cell soma volumes than exercised aged rats, and that exercised aged rats have the same number of Purkinje cells as young rats. The follow-up study indicated that the degree of age-associated degenerative changes in parts of the central nervous system is dependent on earlier life style and health habits and may be prevented or delayed by physical exercise. You and I are not rats, but the implication is that exercise results in greater brain cell strength.
J. Comp. Neurol. 428:213–222, 2000.
The full study can be read here, along with citation and authors.