Review HR2VP: Use your Heart Rate Monitor as a Power Meter

Review HR2VP: Use your Heart Rate Monitor as a Power Meter

The HR2VP app upgrades your heart rate monitor to a power meter by using an algorithm. You can now use Zwift without having a power meter, or use it when exercising (running) with only your heart rate monitor. But does it work properly and does it add value? Read it in this review!

Why convert Heart Rate to Power

HR2VP app

At first you might think converting heart rate to power is impossible and useless. At least that was my first thought. But let’s see how it works and dive into some possibilities. HR2VP is an app that you can easily connect to your ANT+ or Bluetooth heart rate monitor. It converts your heart rate data into virtual power (VP). You can connect it live to your Garmin, Wahoo or other device. Afterwards the app sends your workout to Strava. You can also connect HR2VP to Zwift as if it is a power meter. You can therefore Zwift without having a smart trainer or power meter.

But what if you already have a power meter or smart trainer? You can then use the HR2VP app whenever you exercise without your power meter. For instance at your gym, or when running, or when using your mountain bike when you only have a power meter at your race bike. Why? Because you probably prefer to analyze all your data based on power. Especially when you work with metrics like Training Stress Score (TSS), Fitness (CTL), Functional Threshold Power (FTP), Acute- or Chronic Training Load (ATL/CTL), Intensity Factor (IF) or any other power based metric.

Here you can see a certain heart rate (y-axis) is not directly connected to one and the same power value (x-axis). You would then expect a straight line. Instead, the algorithm takes into account how heart rate reacts on power.

Does it work? Virtual Power vs Actual Power

CycleOps tried to get power data out of there PowerCal heart rate monitor, but that did not work out well. To increase accuracy compared to CycleOps, HR2VP added individual parameters for their algorithm such as resting heart rate, maximum HR, FTP and weight.

But still, how could you predict power based on heart rate, when heart rate has a delay to intensity and a drift during your workout. Simply by adding this to your algorithm, HR2VP thought! They therefore claim to put your watts in the right training zone within 10 seconds. Let’s take you through some pictures.

Here you see the algorithm working. Even though heart rate (red line) is increasing slowly, the algorithm detects a sharp incline in heart rate in the beginning, and therefore spikes virtual power (yellow) immediately. It therefore decreases the delayed feedback of heart rate.
Here you can compare the same interval between virtual power (purple) and actual power (yellow) measured by a Garmin Vector 3. You can see that the patterns look quite the same: a peak in the beginning followed by a little less but stable output later on. You can also see that there is still a little delay. Indeed, of about 10 seconds.
Another example of two 1-minute intervals with 30 seconds recovery. If you smoothen the data, the virtual power (purple) actually seriously matches the actual power (yellow). Again, with a little delay.
Although the algorithm works really well in intervals longer than let’s say 45 seconds, it has some difficulties in sprints. Here you can see the true peak power (yellow) in a 5 second sprint is much higher than the algorithm calculates (purple). The total workload however – represented by the surface underneath both graphs – is quite similar. Therefore you can still use this data to calculate workload.
Even at low intensities (<150watt) and therefore low heart rates the algorithm does its job. These are the very first ~ 30 minutes of my ride. You can see a small underestimation of the algorithm (purple) when comparing with the Garmin Vector 3 power (yellow).
The underestimation in the beginning seems to switch at the and of my ride. Here you can see the last ~ 10 minutes of my 80 minutes ride. Probably due to some cardiac drift, the algorithms (purple) seems to overestimating the true power values (yellow) a little.
When looking at the exact data, I was positively surprised. Here you can see some intervals I performed during my 80 minute ride.

Summary

In the beginning I thought converting heart rate to power is interesting, but not very useful nor accurately possible. Now I think it is useful, even (or maybe especially) when you already use a power meter. Having all workouts expressed in power is a big advantage to mixing heart rate and power data. I also could not believe how accurate the algorithm already is. You can use it afterwards to track training load, but also live when your intervals are longer than about 60 seconds.

Future

When I tested HR2VP I thought of a way to increase accuracy on a personal level. Why not feed the algorithm with both heart rate and power, whenever you use both? So it is more accurate when you only use heart rate. Before I could suggest this idea I already received an email from HR2VP founder Grégory Cordier with a link where you can add a workout with heart rate and power to better estimate your FTP. That looks like a very interesting starting point in the further development of this heart rate to virtual power app. You can download the app from the Google Play Store and Apple App Store. Try it for free or purchase it for about 2 euros per month. Let us know what you think 🙂

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