Snippet: Heart Rate Variability (HRV)

Harrison Armitage
Jun 9
2 min read

Heart Rate Variability (HRV) is the tiny change in time between each of your heartbeats. Even if your heart is beating at 60 beats per minute, it doesn’t beat exactly once every second. Sometimes there’s a little more time between beats, sometimes less, that variation is what we call HRV.

What HRV Tells You About Recovery and Performance

HRV is a powerful window into how your nervous system is functioning, especially the balance between your stress response (sympathetic) and recovery mode (parasympathetic) systems.

A higher HRV generally means your body is relaxed, well-recovered, and ready to perform or train hard.
A lower HRV suggests your body might be stressed, tired, or still recovering from physical or emotional load.

Research shows that low HRV after intense training means your body hasn't fully recovered yet. In contrast, a high HRV is linked to better endurance, improved decision-making, and greater emotional regulation (Leal-Menezes et al., 2025; Kemp et al., 2025).

How to Measure HRV

You can measure HRV using a heart rate sensor or wearable device (like a chest strap or smartwatch) paired with an app. Most devices use either:

RMSSD (Root Mean Square of Successive Differences): reliable and commonly used
Frequency analysis: breaks down your heartbeat data into different “bands” like high frequency (HF) and low frequency (LF)

It’s best to measure HRV first thing in the morning, in a relaxed state. Research confirms that short, daily readings (when taken consistently) are accurate and useful (Macedo et al., 2025).

What High vs. Low HRV Means

HRV Level	What It May Suggest	Training Implication
High	Strong recovery, relaxed nervous system	Good to train or compete
Low	Fatigue, stress, poor sleep, and overtraining	Consider rest or light recovery

Note: “High” or “low” HRV is personal. What’s high for one person might be normal for another, so track your trends over time, not just single numbers.

Can You Improve HRV?

Yes. Daily habits like deep breathing, good sleep, hydration, and regular training (with rest) can all improve HRV. A recent study even found that five weeks of slow breathing exercises increased HRV and improved brain function (Mather et al., 2025).

References

Kemp, A. H., et al. (2025). Heart rate variability in mental disorders: An umbrella review of meta-analyses. Translational Psychiatry, 15(2), 123–135. https://doi.org/10.1038/s41398-025-03339-x
Leal-Menezes, R., et al. (2025). High-intensity interval aerobic exercise delays recovery from heart rate variability: A systematic review with meta-analysis. Clinical Autonomic Research, 35(3), 365–379. https://doi.org/10.1007/s10286-024-01103-7
Macedo, A. G., et al. (2025). Assessing the clinical reliability of short-term heart rate variability. Scientific Reports, 13(5), 142. https://doi.org/10.1038/s41598-025-89892-3
Mather, M., et al. (2025). How daily sessions increasing heart rate oscillatory activity via slow breathing can enhance brain function. Current Opinion in Behavioral Sciences, 45, 101–107. https://doi.org/10.1016/j.cobeha.2025.02.003