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AMA Recap: VP of Performance Kristen Holmes on Heart Rate Variability

April 14, 2021

Our VP of Performance Kristen Holmes sat down for an AMA with WHOOP members live in app, answering all of their most common questions about HRV. Here are a few of the highlights.

By Kristen Holmes

Heart rate variability (HRV) is an extremely valuable metric for understanding your body’s physical fitness and readiness to perform. If you’re not already familiar with the basics, we highly recommend reading our Ultimate Guide to HRV.


If I could only do three things to improve my HRV, what would you recommend? – Alex T.

1) Sleep well & consistently. Getting all the sleep your body needs is a great start, but equally as important is making an effort to go to sleep and wake up at regular times each day. Sleep consistency will boost your HRV by helping to sustain your circadian rhythm, and also enables you to spend more time in REM and deep sleep.

2) Pick your moments to drink alcohol. We’ve found that when WHOOP members report consuming alcohol, their HRV drops by an average of 22 milliseconds the next day and can suppress your heart rate variability for 4-5 days.

3) Get outside in the natural light within 20 minutes after waking up in the morning (and prior to 9 am), and watch the sky change from light to dark in the evening. Natural light triggers biological processes involved with regulating sleep/wake times (see sleep consistency above), energy levels and hormone production. This will also improve alertness, mood and vitamin D production, ability to lose weight, and increase capacity to train, to name a few!

Learn More: 10 Ways to Increase Your Heart Rate Variability


Why is HRV a significant metric in tracking fitness/wellness compared to other physiologic measures? – Oksana C.

Daily measures of HRV can help you learn things about yourself that you didn’t know before, such as how much sleep you really need, how travel affects your recovery, and just how many glasses of wine is one too many! Like any metric though, it is not the complete answer. By recording subjective indicators in the WHOOP Journal you can build a contextual picture that will enable you to see what works best for you, and you can keep applying those marginal gains for sustained performance for years to come.


Is it bad if HRV decreases after a rest day? Shouldn’t rest improve it? – Rajeev M.

It isn’t bad. It just means that your body is still working to adapt to the stress you put on it. “Rest” in theory will improve HRV, but remember that in addition to exercise, HRV is also influenced acutely by hormonal reactions, sleep, metabolic processes, breathing, diet, social connection, cognitive processes, and mental stress. So even though you are doing your best to “rest,” these other factors could be slowing your adaptation. Be patient, focus on lifestyle factors you can control and HRV should bounce back. More on this later…

Learn More: “Self-Rule” Choices You Can Make for Better HRV


What are the most common misconceptions about HRV? – Fern Y.

1) That you can’t modify it. You can (see Question 1 above for my top 3 tips).

2) HRV doesn’t tell me any more than my resting heart rate (RHR). Wrong… Although an elevated RHR has been used as an indicator of pending overtraining, it is a blunt instrument, and by the time it is elevated the damage often has already been done.

3) Daily changes in HRV reflect the previous day’s training volume. A hard session will affect your HRV, but things are rarely that simple, and if they were you wouldn’t need HRV. Sleep, non-activity strain, and psychological stress all influence today’s capacity.


What are your thoughts on meditation to improve HRV? – Richard T.

When you are highly alert and want to be calm, meditation (if you are good at) can be an effective intervention. To me, meditation is very non-specific and for most people difficult to do. I prefer interventions such as Resonance Frequency breathing as it has been shown to be the most effective at mediating HRV. Physiological sighs (double inhale and long exhale) have also been shown to calm the nervous system.

Learn More: Ways to Activate the Vagus Nerve and Boost HRV


What role do calories play in HRV or overall recovery? Regardless of vegan, paleo, meat-based eating approaches, I’d love to know if operating at a deficit to change body composition reduces recovery. – Grace P.

Too few calories, or too many calories, is generally bad for HRV. A simple way to improve HRV is to eat meals at regular times and within a restricted feeding window (8-10 hours). Research over the past decade has revealed an intimate relationship between eating in sync with circadian rhythms and metabolic processes. Generally speaking, eat when it is light out, avoid eating when it is dark out, and aim to fast for at least 12 hours overnight (your body needs at least that to function properly).

Learn More: Podcast 48 – Understanding the Science of Calorie Tracking


Why do some people of the same age have significant differences in HRV? – Fredrik F.

From an article on our blog titled What is a Good HRV? It Varies for Everyone:

“The most important thing to know with HRV is that it is an incredibly personalized metric that differs greatly from one individual to the next. When attempting to figure out what is a good heart rate variability for you, a number of factors such as age, gender, fitness level, lifestyle, environment and genetics must be taken into account. … For the most part, younger people have higher HRV than older people, and males may have slightly higher HRV than females. Additionally, elite athletes (endurance athletes in particular) tend to have greater heart rate variability than non-athletes. However, what represents a healthy HRV varies for everybody. There are many exceptionally fit people who have heart rate variability that is lower than the norm.”

Learn More: Average HRV Range by Age and Gender


Do certain types of medications, for example anti-anxiety medications, affect HRV? – Anthony Philippe S.

In principle, be aware that medication (in general) is one of the most common artificial influencers of heart rate variability. It is important to understand that because most medications treat symptoms instead of the underlying disease or illness, these medications might artificially increase HRV while masking the deeper autonomic function and health of an individual.

In regard to medication, higher HRV values do not automatically mean that you are healthier. If you are taking a medication and your HRV is significantly lower or higher than your demographic, you should consider that your HRV might be artificially skewed. In a study by O’Regan et al, results suggest that reductions in HRV can be driven by the effects of antidepressant medications.


Why isn’t HRV displayed throughout the day like heart rate? – David Y.

Because there are so many factors that influence HRV and it is so variable during the day, it is a difficult marker to interpret (see Sam’s question below for a more in-depth answer). Hopefully in the future we will show HRV as a feedback mechanism during breathwork sessions.


Why does WHOOP calculate HRV Primarily during your last SWS/deep sleep stage each night? – Sam P.

Slow wave sleep (SWS, also known as deep sleep) is a stable state that, in contrast to wake (or even other stages of sleep), is unaffected by internal and external factors. It is a reproducible state that allows a reliable determination of HRV. Deep sleep towards the back-end of sleep is when your body is most at rest and provides the cleanest conditions to take a reading that best reflects how it has adapted to the previous day’s stressors. Taking your unweighted average across all sleep would include a lot of variance as well as conditions that are not as ideal for calculating HRV, leading to less reliable data and a baseline that’s not as meaningful.


Can I expect my HRV to go up significantly as I get in better shape? – Laurent R.

Yes, baseline HRV should improve as you become more fit. That said, be sure to observe the HRV trend in the context of sport and lifestyle demands and behaviors (i.e., training load, relationship load, diet, sleep, etc). This context will help you better determine the meaning of the change and then you can adjust training or lifestyle factors if necessary according to the goal of the current training phase. See my reply to Stephanie’s question next…


Does an increased HRV month over month mean you’re actually getting fitter? And vice versa, does a decreased HRV mean you are less fit? As a crossfit athlete, I go through cycles where I am focused more on strength than cardiovascular training and wonder how I can interpret my HRV during these different cycles. – Stephanie A.

A recent study by Daniel Plews and colleagues found that training phases of high intensity (e.g., above the second lactate threshold) suppressed HRV, while phases of lower intensities (e.g., below the lactate threshold) increased HRV. When interpreting an HRV trend over time, it is key to understand how different types of training will impact HRV in different ways, and as a result not always yield a higher HRV and the end of a training block.

Phases involving moderate intensity aerobic work are likely to cause an increasing HRV trend, while phases of high intensity conditioning with minimal low intensity work will cause a decrease. The absence of low intensity aerobic work results in an absence of the stimulatory effects that this training type has on parasympathetic activity. Additionally, the high intensity training will be more disruptive to homeostasis as a result of greater metabolic demand. In this situation, a progressive decrease in HRV can occur despite no meaningful increase in levels of fatigue.

So, you shouldn’t be alarmed if you observe a decrease in your HRV trend when limiting moderate aerobic work. The best way to test whether your training block was effective is to take a “deload” or taper week, crush lifestyle (long walks, clean food, lots of water, meet sleep need, connect with friends, engage in breathwork, ROMWOD, etc) and see what happens to HRV.

The bottom line when interpreting HRV is that changes (acute and long-term) must always be taken into context. Keep track of training load, training type/content, lifestyle factors (sleep quality, nutrition, stress, etc), and actual performance. These variables are complementary and provide a more complete picture of training status:) Great question.

Learn More: Podcast 108 – World-Class Researcher Dr. Daniel Plews Dives Deep on HRV


Why do some top athletes have low HRV? Are there ever any weird situations where one branch (sympathetic vs parasympathetic) dominating and resulting in lower HRV can actually be beneficial? – Chris K

Great question! Hang with me, this will take a minute. The assumption that HRV alone can predict physiological readiness to perform relies on a direct linear relationship between HRV and R-R interval length–and therefore a direct relationship between HRV and fitness. In most early studies investigating HRV and performance, the subjects observed were only recreationally fit and noted that this assumption does not generalize to elite athletes with a history of a high training load.

For elite athletes with lower resting heart rates, decreases in HRV have been observed. This has been attributed to two processes. The first is a decrease in parasympathetic activity that has been observed to occur with reductions in training load (i.e. tapering). This may also be connected to increased sympathetic activity that comes from pre-competition stress. The second process, known as “parasympathetic saturation,” reflects the saturation of acetylcholine receptors at the myocyte level. A heightened vagal tone then causes longer parasympathetic control and therefore decreases HRV. Generally speaking, the relationship between RHR and HRV is quadratic rather than linear.

Learn More: Podcast 29 – Explaining Heart Rate Variability, with Kristen Holmes and Emily Capodilupo


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Kristen Holmes

Kristen is the VP Performance Science at WHOOP. Before joining WHOOP in 2016, she was the Head Field Hockey Coach at Princeton University. One of the most successful coaches in Ivy League history, Kristen won 12 league titles in 13 seasons, and one National Championship. She was also a 3x All American and a 2x Big 10 Athlete of the year at the University of Iowa, competing in both Field Hockey and Basketball Previously a 7-year member of the U.S. National Field Hockey Team, Kristen blends her background in athletics, coaching, performance technology, psychology and sports performance to drive research and partnership initiatives to strengthen WHOOP as a leader in Human Performance.