Heart Rate Variability is the measurement of variations in each heartbeat, so if your heart rate is 60 beats per minute, that doesn’t necessarily mean that it will beat 1 time per second, but that after 60 seconds you will have 60 beats. What we are looking at when we measure your HRV is the balance in your autonomic nervous system. This is the part of your nervous system that controls the balance between your fight or flight response (sympathetic) vs your resting and digesting (parasympathetic). In general, a higher HRV is better, but unlike resting heart rate, we can’t compare your HRV to anyone else, you need to measure your HRV for the long term (around 20 days) to get a baseline for you before we start to make any judgments.
When we look at your heart rate variability we can pick up:
Because your HRV will lower with added stress on your system many people will report seeing a lower than normal morning HRV and then later that day feeling sick. Athletes will often notice that if their HRV starts trending down and they continue to push their training load, they will be prone to increased soreness or simple overuse injuries, as their bodies simply aren’t adapting to their training. If their HRV continues to remain low following rest, they have officially entered overtraining or under-recovery syndrome. The key when this occurs is to let your body come back slowly, and not push it too much too fast, as this will only extend the overall process.
We are lucky now, HRV used to be difficult to measure, we needed heart rate chest straps and had to make sure to do it first thing in the morning. When waking up you would place the strap on and remain still for around 1 minute while you got a reading. The issue is this had to be done first thing upon waking, and that can be challenging. Now many smartwatches with LED heart rate sensors can take this measure while we sleep and are truly at our most relaxed. There are other devices such as the Oura Ring, or Whoop band that also do this, and all are quite accurate.
Things to remember with HRV are that your HRV can only be compared to your baseline and trending data, so don’t compare yours to a friend or training partner.
It is a measure of overall stress so if the number doesn’t reflect what you think it should be based on your training load, look at your overall life stress, and other factors, and see how changing those affects your numbers.
The more data you have the better. The longer you track your HRV the better the data will be and the more you can learn from it.
I have been tracking my HRV for some time now, a little over 5 years, using both the whoop strap and Oura ring to compare the data. They have both made improvements over the years and are now showing very similar data. My baseline was around 60ms, as I built up my training for Ironman Lake Placid my 7-day average was around 75ms. I am now 3 weeks post race and my 7-day average is 48ms. So what do I take away from that? During my training, I was improving my fitness and overall health, and never hit a point of over-stressing my body to the point that it would not adapt to my training. However, the race itself was such a large stimulus that even 3 weeks later my body is still working to recover. Thanks to this data I am just now slowly returning to light easy low-level exercise. This will ensure that I don’t place too much stress on my body before it is ready to take on the challenge.