In an increasingly digital world, we’re finding more and more uses for heart rate sensors in wearable devices. These devices have endless applications and provide insights on everything from personal activity and fitness levels to healthcare. We know accurate biometric sensor data can lead to accurate fitness and health assessments, but what exactly can we do with these assessments?

What it means for fitness
What it means for health
VO₂ max Aerobic capacity – primary measure of chronic change to cardiovascular fitness Higher VO₂ max is correlated with better performance during aerobic activities Higher VO₂ max is correlated with lower mortality & improved recovery from a cardiac event
[Anderson, Jetté, Kodama, Lee]
Resting Heart Rate (HRrest) HR during an awake period of no exertion Decreasing Resting HR is correlated with increasing fitness Steadily increasing Resting HR is correlated with the progression of  cardiovascular disease
[Arnold, Fox, Nauman]
HR Recovery ΔHR over 1-mintute after intense exercise Higher HR Recovery implies better exercise endurance Higher HR Recovery implies better cardiovascular health
[Ching, Cho, Lipinski, Nishime]
HR Response ΔHR over 1-mintute at the start of exercise Higher HR Response can imply low cardiac readiness for exercise Higher HR Response paired with “chronotropic incompetence” can predict carotid atherosclerosis
[Falcone, Jaqoda, Jae, Maddox, Myers]
Cardiac Efficiency Average cadence divided by average heart rate (at steady state): Cavg/HRavg The higher cardiac efficiency, the less heart beats are needed for all physical activities Steadily declining cardiac efficiency is correlated with the onset of hypertension
[Laine, Sung]
HRV Heart rate variability — statistical variability of RR-intervals HRV  can diagnose psychosocial stress & overtraining in exercise HRV can predict atrial fibrillation &  arrhythmia [Chon, Hohnloser, McManus, Park, Valkama]

Read This: Are You Listening to What Your Heart is Telling You?

VO₂ max    
When it comes to fitness, performance is paramount. Like any muscle, the heart and cardiovascular system grow stronger and more efficient with exercise, so as you get into better shape, your body produces the same amount of work for less beats from your heart. Measurements of both physical activity and the body’s response to physical activity are critical components in determining whether you’re improving and can be measured using  “VO₂ max” (maximal oxygen consumption.)  This determines chronic changes to cardiovascular fitness. The higher your VO₂ max, the better you can expect to perform during aerobic activity. Higher VO₂ max is also associated with lowered risk of mortality and increased ability to recover from a cardiac event.

Resting Heart Rate
The term “rest” may not be the first thing to enter your mind when thinking about fitness, but for heart rate, resting measurements can be a great indicator of fitness levels. Decreased resting (periods of no exertion) heart rate correlates to increased fitness. The more a person can lower their resting heart rate, the more likely they are to slow the progression of cardiovascular diseases.

Heart Rate Recovery
Similarly, measuring “heart rate recovery”, or the heart’s ability to return to normal levels after physical activity, can also predict fitness levels and heart function. A healthy heart will recover at a quicker rate than a less healthy one. A higher heart rate recovery suggests increased endurance and better cardiovascular health. To evaluate heart rate recovery, you look at the difference between your heart rate during activity and your heart rate 1-2 minutes after exercise has stopped.

Read This: Why Hearables Should Be Your Number One Choice for the Gym 

Heart Rate Response
Another useful assessment from your heart rate sensor, taken about a minute into your workout, is “heart rate response.” The main reason for your heart rate response to exercise is physiological, increased activity in working muscles causes an increase in sympathetic nervous system activity. The lower your fitness level, the stronger your heart rate response to exercise. With regular training, your body adapts, and while your heart rate will still increase with exercise, you will have to work harder to achieve the same heart rate increase. A higher heart rate response, paired with chronotropic incompetence, can also help predict carotid artery disease.

Cardiac Efficiency
That same regular exercise can lead to higher cardiac efficiency, which is the ratio of work done by the heart to the energy used to perform the work. The more efficient your heart becomes, the less beats it needs for physical activity. Cardiac efficiency can be a great heart health indicator. A declining heart rate efficiency is correlated with many cardiovascular issues, like hypertension.

Heart Rate Variability

Your physical activity, or stress, on the body can also be assessed using heart rate variability(HRV) or the beat-to-beat variability. This measurement diagnoses psychosocial or mental stress, as well as overtraining in exercise. The impact of stressors on the body is monitored by HRV and relates to fatigue (mental and work capacity) and readiness to perform mental and work tasks. HRV can also predict incidences of arrhythmia and atrial fibrillation. This has been used by professional athletes for some time, but it’s just now beginning to see traction in consumer devices. Valencell recently partnered with Firstbeat, who has some of the most advanced analytics around HRV. For more information on how HRV is measured and what can be learned from those results, check out this Heart Rate Variability Review by Dr. Chris Eschbach, Director of Valencell’s Biometrics Lab.

There are a variety of announcements recently about wearable devices “new” capabilities around atrial fibrilation and arrythmia detection, core body temperature and more. These capabilities are being delivered by the same optical heart rate sensors using PPG that are found in a great deal of wearable devices today. In many ways, we are just scratching the surface of what’s possible.

If you have questions or would like more information on heart rate sensor assessments, please reach out to Also, check out Dr. Steven LeBoeuf’s webinar on the topic here.