80/20 Running: Run Stronger and Race Faster by Training Slower

by Matt Fitzgerald

What all of this means to you is that the relationship between perceived effort and intensity is not a pure one, but is corrupted by fatigue. The effect of fatigue on perceived effort has important practical implications for the use of this metric to monitor and control running intensity. If you do a long run at a steady pace, your intensity, by definition, will also remain steady, but your perceived effort will increase as fatigue sets in. To keep your effort steady, you will have to slow down somewhat toward the end of the run. This is not the most sensible way to use perceived effort to control running intensity, however. Instead, I suggest you use perceived effort to establish the appropriate intensity at the start of a workout or workout segment. Then rely on pace or heart rate to maintain that intensity while allowing your perceived effort to gradually increase as fatigue sets in.