In most runs, the goal is to keep relatively the same effort. Not talking Fartleks, Intervals, etc. Say your goal HR is 150(easy), I find myself trying to keep pace instead of effort. Whatever pace I start with at 150, I aim to keep it. Up hills I press a little and on downs I relax. My heart rate might reach 165 going up a good hill and 135 cruising down. Should I let my pace be a variable and make effort constant or does it matter?