The NBA is using it to help keep the bubble COVID-free. Rory McIlroy and other PGA tour pros use it to keep their golf game at its peak. The NFL Players Association thinks it can help pro football players recover faster, avoid injuries, and have a longer career. What is it?
A. magic, B. cryotherapy, or C. performance-enhancing drugs?
Answer: D. Heart rate variability (HRV). Wearable technology like the Whoop strap and Oura ring rely upon HRV as an indicator of the individual wearer’s overall well-being. By combining HRV with other relevant measures of fitness (like sleep quantity and quality, resting heart rate, and respiratory rate), both Whoop and Oura provide users with an indication of their readiness to cope with stress. Think of HRV as accurate and timely information about your physiology; when used wisely, it’s a potential peak performance game-changer. Despite what you might expect with high-profile users like Prince Harry, Patrick Mahomes, and Lebron James, HRV tools are surprisingly cheap and easy to use.
What you’ll learn in this post:
- What HRV is
- What HRV indicates about your physiology
- What factors impact HRV
- How to use HRV to optimize your training
What is Heart Rate Variability (HRV)?
HRV is a measure of the variation in the timing of successive heartbeats. You probably already know that heart rate (HR) is typically measured using the number of heartbeats per minute (bpm). What you may not know is that each beat does not occur with consistent cadence. If your heart rate is 60 bpm, your heart pulsed an average of once per second. Your heart does not beat every second, on the second, though. Instead, the heart beats something like this: 0.9s, 1.65s, 2.85s, 3.4s, etc. HRV describes the fluctuation in length of heartbeat intervals. A varied mix of short and long intervals represents a higher HRV. Low HRV occurs when the timing remains monotonously steady or closer to an average time value between “R” peaks. See the familiar “spikes” of an EKG below for a graphic depiction:
HRV is a measure of the autonomic nervous system
Your autonomic nervous system consists of two branches: parasympathetic and sympathetic. The sympathetic nervous system, commonly known for the fight-or-flight response, primes the body for physical activity. One of the most frequently cited characteristics of sympathetic nervous system activation is an increased heart rate. Conversely, the parasympathetic response promotes “rest and digest” functions and is generally known to complement the sympathetic nervous system as a natural opposition. Accordingly, the parasympathetic system often acts to slow the heart rate. This internal tug-of-war between sympathetic and parasympathetic actions is the reason for HRV. When your heart rate is responsive to both sympathetic and parasympathetic signals, HRV is generally higher. When one of the two systems dominates autonomic control of your heart rate, HRV is usually lower.
High variance = good… low variance = bad?
HRV is simple, but not quite that simple. A higher HRV is good because it represents strong responsiveness to input from both the autonomic nervous system branches. When neither system is dominating the other, your physiology is indicating a readiness to respond. This is why HRV is a significant factor in Whoop’s Recovery score - a well-recovered individual is ready to cope with stress. A lower HRV usually occurs when the sympathetic system sends stronger signals to your heart than the parasympathetic system. Low HRV is likely if you’re exercising because you need an active sympathetic system to help tune your physiology for performance. But if you’re resting, or if you just woke up, a low HRV is likely indicating that your body is working hard to cope with some sort of stress.
Common factors known to affect HRV
HRV is a good measurement for analyzing your trends over time, not comparing yourself to other individuals. That’s because a range of biological factors out of your control, like age, gender, and other hereditary factors, play a role in HRV. Many factors impacting HRV are under your control, however. Studies have shown that nutrition, including hydration, sleep consistency, and volume and intensity of exercise, can affect HRV. Poor nutrition, hydration, consumption of alcohol, sleep hygiene, and too much stress, in general, will push your HRV lower. Herein lies the value of measuring and managing HRV; HRV provides insight into your physiology without laboratory testing or invasive procedures. Without the objective measurement of stress that HRV provides, estimating stress’s cumulative effect is just guesswork.
Use HRV to better understand your readiness to train and stress response
HRV is an invaluable tool for maximizing recovery and ensuring high readiness levels when you need it most. At a minimum, use HRV for permission to rest and permission to stress.
Dial up or dial back training based on HRV
Take a look at the graphics above. The graph on the left shows my Whoop recovery score for one week in August. Notice that red, yellow, and green recoveries track closely with the peaks and valleys of the HRV graph on the right. Based on relatively high recovery on Tuesday, Wednesday, and Thursday, I executed my physical training as planned (permission to stress). The accumulated stress of three consecutive training days resulted in a low recovery on Friday. Based on this knowledge, I did not train on Friday and instead made a concerted effort to keep strain low, hydrate, and sleep well on Friday night. Deliberate recovery helped me achieve high readiness states on Saturday and Sunday.
The anecdote above describes stressors I was aware of based on my training log, and Whoop provided an expected HRV outcome based on three straight days of physical training. I find even more value in the information HRV provides when my recovery is unexpectedly low, or when how I feel doesn’t match what my physiology indicates. The 29th and 30th of September are a great example of this sort of a mismatch. Notice a high recovery on Tuesday, September 29th, paired with a relatively low strain for that day. Despite feeling great when I woke up on Wednesday, a low HRV of 49 combined with other factors to indicate a poor recovery. Since my physiology revealed low readiness for strain, I chose to take another day off before returning to my training plan (permission to rest).
Wearables can't do it all, though
Biometric data collection via a wearable device is not a panacea for better physical training. Principles like overload, specificity, and progression still matter. Much like you can’t outrun poor nutrition, you can’t “out-data” a lousy training program. Likewise, monitoring HRV may help you identify habits that negatively impact your physiology, but it’s still up to you to change your behavior.
Final thoughts
Simply put, all physical training programs are organized bouts of stress. Well-planned training programs balance stress and recovery to maximize training adaptations. However, no training plan could take into account the myriad external factors also impacting the stress response. Deadlines at work, a looming deployment, relationship issues, and newborn babies not keen on sleep are all examples of external factors that could throw even the best training plan off balance. HRV is an invaluable tool for maintaining balance, and more importantly, avoiding the harmful effects of overtraining. In the hands of the right user, HRV is a peak-performance game-changer.