Bite Size - HRV, Just What Is It?

Updated: Dec 24, 2019


In my last post, The next big thing, HRV i discussed the merits of HRV and why, now I am convert. So just what is HRV and in more technical detail what does it mean for you the athlete?

Heart rate variability (HRV) is a relatively new method for assessing the effects of stress on your body. It is measured as the time gap between your heart beats that varies as you breathe in and out. Research evidence increasingly links high HRV to good health and a high level of fitness, whilst decreased HRV is linked to stress, fatigue and even burnout.

Now we have that out of the way what does it mean?

HRV reflects how strong your recovery system the parasympathetic nervous system is currently. When it is low, it will take the body longer to recover from hard sessions and it indicates to the athlete that they need to spend more time recovering. Conversely, when it is high, an athlete will bounce back from intense work much more quickly.

The idea is quite simple. Monitor your HRV every morning and train as normal. If your HRV drops significantly, take this as an early warning that you are overloading the system. A small drop is OK as long as you recover. Training is, after all, about stress and recovery and a hard session, especially on top of accumulated fatigue, will lower your HRV.

But if your HRV stays low even with rest you could be on the edge of trouble. In my opinion, using daily HRV to monitor training stress is the best thing you can do to make your training safe and effective. So listen to your heart.

Until recently Heart Rate Variability could only be tracked via a lab-grade EKG assessment, but now, thanks to the rapid development of mobile app technology, it has become a standard feature on many tri watches. It’s a huge step forward over traditional metrics, like resting heart rate. Heart Rate Variability is a far more sensitive measure of the status of the autonomic nervous system.

Accuracy of the data can vary from app to app, but those apps that use heart rate chest straps tend to be most accurate.

While the latest technology will crunch the numbers and give you the most vital data, you must first get baseline Heart Rate Variability numbers before you can effectively implement those values. This means tracking Heart Rate Variability for at least a month (during a regular training cycle) to establish what your “normal” range should be.

How Heart Rate Variability Is Measured

Say your resting HR is 60 beats per minute. A Heart Rate Variability-calculating device measures the interval between each of those beats, in milliseconds, over a specific period of time, like ve minutes, then crunches the numbers to assign a Heart Rate Variability score. If the intervals between beats are about the same, your HRV score will be low, indicating you need to take it easy.

If it varies, your score will be higher, and you’re ready to rock.

Taking your HRV reading daily lets you plan ahead with knowledge of what your body is best suited to on that day. When your reading is good compared to your baseline, it’s having confidence that your body is able to cope with the training demands you put on it. Not only that, but research summarisedthat when a group of recreational club runners trained over an 8 week period, those whose HRV increased improved their running times in the final race, whereas those whose HRV stayed the same or declined did not improve.

Similarly, another study on elite swimmers demonstrated that their performances in a weekly 400m time trial could be accurately predicted from their HRV. This makes HRV an ideal tool to use with polarised, or high intensity interval training (HIIT). High intensity sessions are a very effective stimulus for the body to adapt but need to be performed on days when the body has adequate reserves. Training hard on these days will be more effective and will feel better than training hard on days when you’re not fully recovered.

Similarly, HRV is a great tool to use in the taper period before a race or event so you know you are peaking and ready to perform at your best when you want to. As well as allowing you to vary your training according to your body’s needs, using HRV to record subjective feelings of stress, fatigue, mood and your diet and sleep quality allows you to discover which factors affect not only your recovery, but your overall health.

Sisu Racing World Class Triathlon Coach


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