Running · 2 min read
Running watches now generate more data than a runner can readily act on. Heart rate, pace, power, cadence, training load, VO₂ max estimates — all of it available without any lab testing. The question is which of it actually matters for training decisions.
By Chris Gkoufas, DVOTION ·
Most of the metrics produced by running watches are estimates. VO₂ max is estimated from heart rate and pace data. Training zones are estimated from age-based formulas. Training load is calculated from internal algorithms that vary by device.
Estimates are not useless — they can be consistent indicators of trends. But they are not substitutes for measured data. A runner whose watch estimates their VO₂ max at 52 might actually be anywhere in a wide range depending on their physiology, running economy and the algorithm used.
The most useful data for training decisions, in order of reliability and actionability:
1. Tested lactate thresholds — these determine where your training zones actually sit 2. Tested VO₂ max — this gives a real aerobic ceiling, not an estimate 3. Heart rate at known intensities — useful for tracking aerobic drift and recovery 4. Pace at known efforts — useful for tracking aerobic adaptation over time 5. Cadence — useful indicator of running efficiency when combined with other data 6. Heart rate variability — useful as a recovery and readiness indicator if tracked consistently
For casual runners with no specific performance target, watch data is often sufficient. Heart rate zones estimated from age, pace tracking, and general training load give enough information to train consistently and progressively.
For athletes with specific targets — sub-3 marathon, HYROX qualifier, ultramarathon — the gap between estimated and tested data becomes more significant. Training at the wrong zones means either under-stressing the aerobic system or accumulating unnecessary fatigue.
When a runner tests their lactate thresholds, they often discover their easy zone is faster or slower than they thought. Their threshold pace — where tempo work should sit — is specific rather than estimated. Their zones are built from their physiology, not from a formula.
This affects every session. Easy runs are genuinely easy. Threshold sessions are at the right intensity. High-intensity work is correctly placed. The overall training distribution, which is one of the strongest drivers of endurance development, becomes accurate.
They are reasonably consistent as trend indicators but not accurate as absolute measurements. Studies show they can be off by a meaningful margin depending on the individual.
For most runners, Endurance Performance Profiling gives the most directly useful data, because it combines respiratory testing with a progressive blood lactate profile: your thresholds, your curve and training zones in your own pace or power.