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HRV: Heart Rate Variability

How to better manage all your training and life stresses

The physiological concept of heart rate variability has been in the medical community for many years. Measurement of HRV reached the endurance community about 10-20 years ago. At that time, the research was unclear about the role HRV could play in helping to manage a triathlete’s training load combined with work and life stresses. Stronger evidence for the use of HRV and more ways to measure it are now more mainstream. New measurement tools that are easy to use and affordable are making this technology available and easily applicable to all levels of athlete.

What is HRV?

Heart rate variability is a measurement of heart beat irregularity or the variation of the time interval between successive heartbeats; it’s measured by the variation in the beat-to-beat interval. Further, It’s a measurement of the space between R waves in the sinus QRS wave. If you’ve ever seen an EKG, you’ve seen the QRS wave. This is a normal heart rhythm. In a normal beating heart, the time between these beats is not exactly the same. The medical community has identified multiple disease states related to lower HRV, such as congestive heart failure. It’s also used to monitor patients after a heart attack.

Although HRV manifests as a function of heart rate, the signals originate in the nervous system. Heart rate and rhythm are controlled by the autonomic nervous system (ANS). The two branches of the ANS are parasympathetic (PNS – rest and digest) and sympathetic (SNS – fight or flight) nervous systems. Because HRV reflects the status of your ANS, it has applications to monitor overall recovery status and readiness to train. Gone are the days of checking only morning resting heart rate to understand your recovery and readiness status.

How HRV helps manage training and life stresses

HRV, in its simplest form, is a way to assess the effects of total stress on the body. Looking at trends in HRV reflect the accumulation of total load over a specific period of time. It is the sum of mental, nutritional, and physical stresses on the body. Devices measure HRV as a score. Increasingly, research is showing that a high HRV score indicates good health and fitness; a low score can indicate high stress loads, fatigue and even burnout. When using HRV, it’s important to look at both daily drops and trends over time. When a score is consistently low for several days and is not coming up, this is a clear indication to take more rest before bigger problems occur. Small dips may simply be a reflection of the normal stress-recover cycle of daily training.

On a deeper level, a low HRV score means: a decrease in the time between R waves, increase in excitement and an increase in SNS activity. Low scores will be seen after intense or long training days, competition, or strength training. Yet, an athlete may experience a lower HRV preceding competition as a result of higher levels of excitement.

When an athlete experiences fatigue reflected by HRV, workout or race performance may or may not suffer. HRV will typically show changes before performance decrements and may serve as an early warning sign of fatigue accumulation. Do not expect your performance to be poor based solely on a low HRV score. (4)

Many devices and technologies help us to monitor training stress: power, heart rate, speed, pace distance, elevation, etc. Coaching software helps to calculate, evaluate and plan training around training stresses and planned recovery. It makes my job as a coach much more robust because I can plan training and recovery based on all of this great technology. The real challenge lies balancing all the other stresses in your life to devise optimal training and race outcomes. This is where HRV monitoring can be valuable to both coach and athlete. It’s a great way to demonstrate how nutrition and hydration status, lack of sleep, long commute times, travel and too much activity on rest days has a negative impact on day-to-day training performance and long term race performance. Monitoring HRV over time is a powerful coaching and training tool.

Devices, apps and software

Monitoring HRV is relatively simple and can take as little as one minute per day. Measure in the morning and follow the day’s activities and training as usual. Here are some of the devices and apps available:

  1. iThlete – One of the original HRV measurement tools. More precise tracking of parasympathetic activity; Robust website and app, coach and team level software, pro level for in depth analysis of multiple metrics; Great for more serious or elite athletes; Great education tools for athletes and coaches. iOS and Android app available. Requires external device for finger measurement.
  2. HRV4Training – Easy to measure with finger on phone camera; Robust website and app, coach and team level software, pro level for in depth analysis of multiple metrics. This app is great for more serious or elite athletes; Great education tools for athletes and coaches. There is an option to input daily metrics in addition to HRV. iOS app only
  3. Whoop strap – Watch-like device wearable 24/7. Very easy to use and measures throughout the day and night. Fairly pricey with extra payment for website membership. Great for more casual athletes or those who don’t have time or interest in additional steps
  4. Other: elite HRV – iOS app only; SweetBeat – iOS app only; Apple watch, BioForce, Vital Monitor, HR monitor straps: Polar, Wahoo, Garmin, etc. Most integrate with TrainingPeaks.
    Benefits and limitations

The benefits are pretty clear on HRV application in triathletes. The biggest benefit is improved performance using an HRV guided approach to planning and implementing training. One of the most recent research articles on HRV compared performance in cyclists. One group trained with HRV and one group followed a traditional coaching plan. The most important conclusion was that in the HRV trained group all measured power numbers improved: from peak power (14 percent) to a 40-minute time trial (7 percent). The traditional group’s numbers showed only minor improvements.

It’s important to note:

“A key difference between this research and some earlier studies on HRV-guided training is that the weekly average is used, as opposed to the daily HRV score. This places a greater emphasis on accumulated fatigue over the short term, and is analogous to Acute Training Load (ATL – “fatigue”). The difference between the two is the fact that internal load is being assessed rather than external load with ATL and Training Stress Score (TSS).” (Wegerif, 1)

Other benefits include: prevention of over training syndrome and providing a more accurate and robust way to monitor rest, recovery and sleep.

Some of the limitations to using HRV include the ability to remain flexible in the planning and training process. And, it’s most robust when the athlete remains engaged in this tracking process as HRV works best when taken 5-7 days per week, daily preferred. HRV is a great tool to learn to listen to your body.

The human element is always present. Are you using the device correctly? Using HRV can be helpful when your coach is not local. Constant communication with the athlete will always provide more information as to what may be causing readings that don’t make sense. There is no one device (at least yet!) that can measure everything accurately every day. Look to your coach to always have the objective perspective to help you decide if you should or should not go through with a workout as planned. There is a time to push through fatigue and a time to honor it and rest.

When choosing a device or app to use, much depends on your goals and time commitment to training coaching and level of expected race performance (podium at major competition or complete a local sprint). It is more work for both the coach and athlete, so choose your platform and device accordingly.

In conclusion, training with HRV has great potential to help you achieve optimal performances. It can take a little time to learn about the various platforms available and which one makes the most sense for you. Look to your coach to help you understand how to use it and what all the data means to you.


1. Wegerif, Simon. New study widens HRV evidence for more athletes. TrainingPeaks blog. 28 August 2018
2. Javaloyes, A., Sarabia, JM, Lamberts, RP, Moya-Ramon, M. Training Prescription Guided by Heart Rate Variability in Cycling. International Journal of Sports Physiology and Performance. 2018, 1-28.
3. Heart rate variability. Wikipedia.
4. Flatt, Andrew. Intrepreting HRV trends in athletes: High isn’t always good and low isn’t always bad. Website: Simplifaster. August 2017.

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