I&#x27;m not sure if this is a semantic difference, but how do you know it would take less &#x27;effort&#x27; to get the heart rate up for out of shape people? I think &#x27;less intensive exercise&#x27; would be better phrasing.<p>Heart rate is a pretty good proxy for &#x27;effort&#x27;. As you get in better shape, your body is more efficient at all sorts of tasks, including fitness challenges, so to get your heart rate higher, you have to increase the intensity of the activity.