Effort as a dimension of spontaneous activity in rats

The relationship between effort and voluntary activity was studied in a braked running wheel and a voluntary treadmill. Effort was manipulated by varying the torque required to turn the wheel and by changing the angle of inclination of the treadmill. In both situations distance run was a linear decreasing function of effort, and work accomplished was a nonmonotonic increasing function of effort. These findings are discussed in relation to responsivity and regulatory views of the genesis of spontaneous activity.