Blog post by Marco Altini
One of the most interesting ways to analyze heart rate variability (HRV) data is to look at the amount of day-to-day variability in your HRV scores. That's what we call the Coefficient of Variation (CV HRV)
The CV HRV is different from your baseline, which is simply the average of your scores over a week. In simple terms, the CV HRV reflects how much your scores jump around on a day to day basis.
Why do we care?
Normally, the most important aspect to analyze is how your baseline is going with respect to your normal values.
A baseline within normal values shows a stable physiological condition and good adaptation (check out this blog for more information about the normal range)
However, the amount of day to day variability (the CV HRV), combined with baseline changes with respect to normal values, can provide additional insights on adaptation to training and other stressors.
The CV HRV can flag issues in response to stress, before a baseline reduction. Quoting Andrew Flatt ”the preservation of autonomic activity and less fluctuations (reduced CV HRV) seem to reflect a positive coping response ... In fact, individuals who demonstrated the lowest CV HRV during increased load showed the most favorable changes in performance"
A reduced CV HRV is often associated with coping well with training. This means also that larger fluctuations in CV HRV are signs of poor adaptation and might reflect issues in maintaining homeostatic control.
How do you use the CV HRV?
Let's look at one example.
I've discussed before how "work stress" is what drives changes in HRV for me (that's where I need to "perform"). Below you can see two similarly stable HRV trends (in the boxes), as well as my increasing subjective stress.
What about the CV HRV? Was it capturing anything differently?
Let's look at the data.
We can see how the HRV response to increased stress was still within my normal range but included a lot of jumping around (high CV), which represents a poor response, eventually leading to suppressed HRV.
Only reducing the stressor finally caused a rebound to normal.
The CV HRV had captured very well the poor response.
Learning what drives big changes in stress is probably the first step to do something about it, whenever it's possible.
Ideally, in the medium term, these are good trends we should hope to see if we are responding well to the various stressors in our lives:
Pay attention to deviations from these trends to spot potential issues in advance, which is easy to do in the HRV4Training app.
You can learn more about trends in resting physiology, in this blog post. I hope you have found this blog informative!
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This blog is curated by
Marco Altini, founder of HRV4Training
The Ultimate Guide to HRV
1: Measurement setup
2: Interpreting your data
3: Case studies and practical examples
1. Intro to HRV
2. How to use HRV, the basics
3. HRV guided training
4. HRV and training load
5. HRV, strength & power
6. Overview in HRV4Training Pro
7. HRV in team sports
1. Context & Time of the Day
3. Paced breathing
4. Orthostatic Test
5. Slides HRV overview
6. Normal values and historical data
7. HRV features
1a. Acute Changes in HRV
1b. Acute Changes in HRV (population level)
1c. Acute Changes in HRV & measurement consistency
1d. Acute Changes in HRV in endurance and power sports
2a. Interpreting HRV Trends
2b. HRV Baseline Trends & CV
3. Tags & Correlations
4. Ectopic beats & motion artifacts
5. HRV4Training Insights
6. HRV4Training & Sports Science
7. HRV & fitness / training load
8. HRV & performance
9. VO2max models
10. Repeated HRV measurements
11. VO2max and performance
12. HR, HRV and performance
13. Training intensity & performance
14. Publication: VO2max & running performance
15. Estimating running performance
16. Coefficient of Variation
17. More on CV and the big picture
18. Case study marathon training
19. Case study injury and lifestyle stress
20. HRV and menstrual cycle
21. Cardiac decoupling
22. FTP, lactate threshold, half and full marathon time estimates
23. Training Monotony
Camera & Sensors
1. ECG vs Polar & Mio Alpha
2a. Camera vs Polar
2b. Camera vs Polar iOS10
2c. iPhone 7+ vs Polar
2d. Comparison of PPG sensors
3. Camera measurement guidelines
4. Validation paper
5. Android camera vs Chest strap
6. Scosche Rhythm24
7. Apple Watch
9. Samsung Galaxy
1. Features and Recovery Points
2. Daily advice
3. HRV4Training insights
4. Sleep tracking
5. Training load analysis
6a. Integration with Strava
6b. Integration with TrainingPeaks
6c. Integration with SportTracks
6d. Integration with Genetrainer
6e. Integration with Apple Health
6f. Integration with Todays Plan
7. Acute HRV changes by sport
8. Remote tags in HRV4T Coach
9. VO2max Estimation
10. Acute stressors analysis
11. Training Polarization
12. Lactate Threshold Estimation
13. Functional Threshold Power(FTP) Estimation for cyclists
14. Aerobic Endurance analysis
15. Intervals Analysis
16. Training Planning
17. Integration with Oura
18. Aerobic efficiency and cardiac decoupling
1. HRV normal values
2. HRV normalization by HR
3. HRV 101