How quickly humans and other animals take decisions and move often covary with the utility of their goals, suggesting the existence of a shared mechanism controlling the speeds of action selection and execution. To test this hypothesis, we developed a self-paced foraging task in which rats run back-and-forth across a motorized treadmill to collect drops of water, and separately manipulated reward and effort. We used simple models to 1) quantify changes in running speed and in the pause between runs (run and inter-run durations) and 2) explore algorithmic and neural principles controlling these processes. As expected, inter-run and run durations increased as the animals became satiated. Sequences of unrewarded runs led to longer pauses but, surprisingly, did not slow down running speed. In contrast, in response to effort manipulations, rats modulated their running speed to maintain reward rate constant, without much changes in inter-run duration. Finally, individual differences in running speed modulation across effort manipulations were explained by the rats' unique sensitivity to movement cost, which was selectively increased by lesions of the dorsal striatum. Our work provides new insights into the mechanisms controlling vigor and highlights the contribution of the dorsal striatum in shaping motor cost sensitivity.