Key takeaways
Resting heart rate drops as aerobic fitness rises; illness, alcohol and poor sleep push it up and HRV down
Watch the rolling 7-day HRV average rather than single mornings, as research on elite athletes supports
If resting HR is 5+ beats above normal, HRV is well below range and you feel off, take an easy day or rest
Your VO2max changes over weeks. Your resting heart rate (RHR) and heart-rate variability (HRV) change overnight. Used well, they tell you when to push and when to back off.
What they measure
- Resting heart rate: beats per minute at rest, best measured during sleep or right after waking. Fitter hearts pump more blood per beat, so RHR drops as aerobic fitness rises.
- HRV: the variation in time between heartbeats. Higher HRV generally reflects a stronger "rest and digest" (parasympathetic) influence; lower HRV reflects stress, fatigue, illness or alcohol.
What moves them
| Factor | Typical effect |
|---|---|
| Aerobic training over months | RHR ↓, HRV ↑ |
| A very hard session or race | RHR ↑, HRV ↓ for 1–3 days |
| Poor or short sleep | RHR ↑, HRV ↓ |
| Alcohol | RHR ↑, HRV ↓ — dose-dependent, especially in the first hours of sleep |
| Illness, fever | RHR ↑ (often several beats), HRV ↓, sometimes before symptoms |
| Heat, dehydration | RHR ↑ |
| Psychological stress | HRV ↓ |
A large real-world study of Finnish employees (Pietilä et al., 2018) found that alcohol reduced overnight recovery measured by HRV in a dose-dependent way — even low doses had a measurable effect, and high doses a large one.
How athletes use them
Research on elite endurance athletes (Plews and colleagues, 2013) supports watching the rolling 7-day average of HRV rather than single mornings:
- A stable or rising trend while training normally = adapting well.
- A clear drop over several days with higher RHR = accumulated fatigue, illness coming, or life stress. Make the next sessions easier.
- One bad morning after a late night means little. Look at trends.
A simple routine
- Let the watch record overnight values; don't chase daily scores.
- Know your normal range (last 4–8 weeks).
- If RHR is 5+ beats above normal and HRV is well below range and you feel off → easy day or rest.
- If the numbers are bad but you feel great, do your warm-up and decide then.
- Long term, expect RHR to drift down as your VO2max improves.
Recovery is also where training turns into fitness — the topic of why some people improve more.
Frequently asked questions
What does a low HRV mean?
Lower HRV reflects stress, fatigue, illness or alcohol, while higher HRV generally reflects a stronger rest-and-digest influence. One low morning means little; a clear drop over several days is the signal to ease off.
Does alcohol affect HRV?
Yes. A large study of Finnish employees found alcohol reduced overnight recovery measured by HRV in a dose-dependent way, with a measurable effect even at low doses and a large one at high doses.
Why is my resting heart rate higher than normal?
A hard session or race, poor sleep, alcohol, heat, dehydration or an illness coming on can all raise it, sometimes by several beats and before symptoms appear. Compare it with your normal range over the last 4 to 8 weeks.
Sources
- Plews DJ, et al. Training adaptation and heart rate variability in elite endurance athletes: opening the door to effective monitoring. Sports Med, 2013.
- Pietilä J, et al. Acute effect of alcohol intake on cardiovascular autonomic regulation during the first hours of sleep in a large real-world sample of Finnish employees. JMIR Ment Health, 2018.