Jul 29, 2026 · 15 min · 11 segments
Heart rate or pace? For years, runners have debated which is better, but both measure different parts of the same effort. In this episode, CTS Director of Coaching Cliff Pittman explains why RPE is…
Now, let's start with what heart rate actually measures, because that's where this whole problem begins.
Heart rate measures cardiovascular strain, and that's the only thing it measures.
It doesn't tell you anything about metabolic cost or mechanical loading, and cycling is actually where this limitation became obvious.
Once power meters showed up, coaches could finally hold power output constant and watch what heart rate did over the course of a ride.
What they found was that a rider could hold the exact same power output for an hour, and heart rate would still climb, drifting from Zone 2 into Zone 3, while the actual output never changed at all.
Now, that gap is the reason cycling moved off of heart rate and onto power as its primary training metric, because it proved heart rate couldn't be trusted to represent output on its own and shouldn't be the target for exercise intensity prescription.
Now, it's still a valid measure of cardiovascular stress, but not metabolic or mechanical.
A power meter measures mechanical output directly and precisely, since watts are watts regardless of wind, grade, or fatigue state.
It isn't measuring metabolic cost itself the way that ventilation or gas exchange would in a lab.
Because pedaling efficiency stays remarkably stable for a given rider, power output becomes an extremely reliable proxy for metabolic costs, precise enough that a coach can prescribe intensity with something close to surgical accuracy.
Now, let's start with what heart rate actually measures, because that's where this whole problem begins.
Heart rate measures cardiovascular strain, and that's the only thing it measures.
It doesn't tell you anything about metabolic cost or mechanical loading, and cycling is actually where this limitation became obvious.
Once power meters showed up, coaches could finally hold power output constant and watch what heart rate did over the course of a ride.
What they found was that a rider could hold the exact same power output for an hour, and heart rate would still climb, drifting from Zone 2 into Zone 3, while the actual output never changed at all.
Now, that gap is the reason cycling moved off of heart rate and onto power as its primary training metric, because it proved heart rate couldn't be trusted to represent output on its own and shouldn't be the target for exercise intensity prescription.
Now, it's still a valid measure of cardiovascular stress, but not metabolic or mechanical.
A power meter measures mechanical output directly and precisely, since watts are watts regardless of wind, grade, or fatigue state.
It isn't measuring metabolic cost itself the way that ventilation or gas exchange would in a lab.
Because pedaling efficiency stays remarkably stable for a given rider, power output becomes an extremely reliable proxy for metabolic costs, precise enough that a coach can prescribe intensity with something close to surgical accuracy.
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