Pace dropped while heart rate stayed flat: detecting accumulated fatigue
An ordinary Tuesday from the demo profile containing 2,325 workouts since 2021: a five-repetition threshold session. The athlete saw three numbers, but their significance only becomes clear in the context of the training week.
What the watch showed
- Average heart rate of 137 bpm — apparently normal and consistent with other sessions that month.
- Training load of 90 — above average, earning an excellent rating from the watch.
- Three of five repetitions within target range — on the fourth, pace dropped by 6 seconds per kilometre while heart rate stayed flat.
What the coach saw
The key combination was pace dropping while heart rate stayed flat. If the athlete had simply been unwilling to push, heart rate would probably have fallen as well. An all-out effort would usually have driven it upwards. A heart rate that fails to rise as pace deteriorates suggests a blunted cardiovascular response: a classic sign of accumulated fatigue rather than lost fitness.
The watch did not recognise that combination; a load of 90 simply looked like an excellent workout. The coach assessed both the trend within the repetitions and the context of the week.
Decision and plan adjustment
The session was cut to three repetitions and Thursday became an easy day. Weekly ACWR returned to 1.14: progression remained, but without an excessive spike. Marathon-specific quality was not sacrificed; two unplanned heroic repetitions would have been costlier than one omitted rep.
The decision referenced Endurance Training Periodisation, chapter 11, one of more than 200 books and articles in Skol’s knowledge base. Read more about load management in the easy-volume guide and the ACWR calculator.
What to apply to your own training
- Assess the pace–heart-rate relationship within the session rather than relying on average heart rate alone.
- Pace down with flat heart rate can indicate fatigue. Pace down with rising heart rate may suggest heat, dehydration or simply a difficult day. Stable pace with unusually low heart rate can indicate improving fitness.
- Shortening one session when the signal appears is preferable to losing a week to overtraining.
FAQ
Why does heart rate stay low when I am fatigued?
With accumulated fatigue, sympathetic responsiveness can be blunted: the heart does not reach its usual working rates even though the effort feels hard. Being unable to raise your heart rate can therefore be a reason to reduce load, not push harder.
Is a training load of 90 inherently bad?
No. In isolation, it can be a productive training dose. The problem is its timing: high load on a day when the body is already showing fatigue. The same number could be entirely appropriate when you are fresh.
How does SkolCoach distinguish fatigue from a one-off bad day?
Through context: sleep and HRV from previous nights, total weekly load and trends within the repetition series. No single number determines the verdict; the decision comes from converging signals. You receive the same analysis once your devices are connected.
See how it works with your own data
Connect your watch and sensors — SkolCoach will import your history, assess your current fitness and map out the next steps. Get 30 days of Pro free — no card required.
Start for free