HRV and Readiness Scores: What They're Worth

Heart rate variability is a real physiological signal. A single proprietary readiness number is a long way downstream of it.

What this is

Heart rate variability measures the variation in time between heartbeats, which reflects autonomic nervous system activity. It's a legitimate physiological measure with a large research literature, and it responds to training load, sleep, alcohol, illness and stress.

Two things get lost between that and the number in your app. First, absolute HRV varies enormously between individuals — comparing yours to a friend's is meaningless, and only your own trend carries information. Second, a readiness score is a proprietary blend of HRV, resting heart rate, sleep and recent activity, and none of the vendors publish how it's weighted or validated.

What the evidence says

  • HRV reflects autonomic state and responds to load, sleep and alcohol

    Gold· human data

    Extensively studied. Alcohol in particular produces a large, reliable overnight drop, which is one of the more useful things a device will show you about your own behaviour.

  • HRV-guided training can improve endurance outcomes

    Silver· human data

    Systematic reviews and meta-analyses of HRV-guided versus predefined training report promising results for measures including VO2max, from a small number of trials with varied protocols. Genuinely interesting, not settled.

  • Only your own HRV trend is interpretable

    Gold· human data

    Between-person variation is large and driven by age, genetics, fitness and measurement method. Absolute comparisons between people are not informative.

  • Measurement conditions dominate the reading

    Gold· human data

    Time of day, body position, breathing rate and recent food or caffeine all move HRV. Overnight or on-waking measurement under consistent conditions is the only way to get a comparable series.

  • A proprietary readiness score reliably tells you how hard to train

    Unproven

    The inputs are real; the composite and its weighting are unpublished and unvalidated. It's a prompt to check in with yourself, not an instruction.

What this means in practice

  • Track your own baseline for a few weeks before drawing any conclusions.
  • Measure under consistent conditions — overnight, or on waking before getting up.
  • Watch the rolling trend rather than single days; day-to-day noise is large.
  • Treat a low reading as a prompt to consider sleep, alcohol, illness and load — not as an instruction to skip training.
  • If your own perception and the score disagree, your perception plus a look at the week's training usually wins.

When to see a doctor

  • A sustained unexplained rise in resting heart rate with fatigue or breathlessness.
  • Palpitations, chest discomfort or fainting.
  • Performance declining as training increases — look at fuelling and total load rather than the score.

The honest summary

HRV is real and your own trend is genuinely informative, especially about alcohol and sleep. The single readiness number on top of it is an unpublished formula — useful as a nudge, not as a coach.

Work it out

See also

Frequently asked questions

What is a good HRV?
There isn't one. Absolute HRV varies hugely between people by age, genetics, fitness and measurement method. Only your own trend under consistent conditions means anything.
Should I skip training when readiness is low?
Treat it as a prompt to think about sleep, alcohol, illness and accumulated load — not an instruction. HRV-guided training trials are promising but small, and the vendor score isn't the same thing as the HRV research.
Why does alcohol tank my HRV?
Alcohol raises sympathetic activity and disrupts sleep, producing a large and reliable overnight drop. It's one of the clearest, most repeatable signals a wearable will ever show you.

Sources

Written and reviewed by Mathew Beale, MSc Biotechnology, University of Reading.

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