If you like using heart rate data to get the most out of your training but you’re ready to ditch the cumbersome chest strap, then optical heart rate sensors might be for you.
Mio Link Strapless Heart Rate Monitor and Optical Heart Rate Technology
Instead of directly measuring electrical impulses in the heart the Mio Link detects your pulse by shining light into your wrist. It sounds bizarre, but this new technology could make chest straps a thing of the past. Mio Global is leading the charge, and their recent partnership with Garmin will usher in a new era of wearable sports technology.
Mio Link Summary
I was skeptical when I first saw optical heart rate technology and, at the time, I was right. CNET posted a review last year on wristband HRMs (heart rate monitors), basically stating they are terrible and get even worse when you start moving; even if these devices could measure your heart rate accurately at rest, it was challenging to detect fast pulses in a real world environment. Luckily, technology has come a long way in the last year (and CNET failed to review Mio), and Mio’s heart rate sensors are the best of the bunch. But are we really ready to ditch tried-and-true chest straps for good?
Garmin may just think so. Although they just released their advanced HRM-RUN chest strap that measures vertical oscillation, ground contact time, and cadence in addition to heart rate last year, Garmin is now on board with optical heart rate technology. This May, they partnered with Mio and became the first of the big three (Garmin, Suunto, Polar) to release a GPS watch with an optical sensor built directly into the watch: the Garmin Forerunner 225.
Mio uses the same sensor in all of their wristbands, and I have a hunch that we’ll see the same sensor implemented in more Garmin devices in the near future. Naturally, Suunto and Polar will have to release competing products. If wrist based HRMs are the future, then I have to put the tech to the test. I purchased the Mio Link, which connects via Bluetooth or ANT+ to your favorite GPS device or smartphone, and put it through 50+ workouts before writing this review.
The good and the bad.
Obviously, having a wristband HRM offers some advantages to a chest strap. Even better, with the Garmin 225, you don’t need an external HRM at all. Comfort and convenience typically come at a high price, but the price tag of the Mio Link is comparable to a traditional chest strap and cheaper than a premium chest strap. And if you’re getting the Garmin 225 or a future watch with a built in sensor, you won’t have to spend money on an external HRM at all. It’s the best of both worlds! That said, there are some drawbacks as well. Premium HRM chest straps like the Garmin HRM-RUN offer more data than just pulse rate, and it’s simply impossible to get this data from a wristband. If you’re looking for more sophisticated data, you’re going to have to wear a chest strap. Plus, constantly shining light into your wrist demands a lot more power than simply detecting an impulse, so there are some battery life limitations that need to be addressed. Apparently, this technology may work better on certain skin colors than others, and users with tattooed wrists might find that optical HRMs aren’t good at sensing through ink. Finally, despite being a definite step in the right direction, there are some heart rate related issues that I’ll get into with more detail below.
Mio Link Features
The Mio Link is the simplest of all the Mio products. It features Mio’s optical heart rate sensor built into a silicon wristband, one button, and a single LED light; that’s all. The LED serves multiple purposes: the color and flashing pattern of the light gives you information about your heart rate and battery life. Other than that, it couldn’t be any simpler. Just turn it on, connect your GPS/phone to it, and go. This particular unit goes for $79 on Amazon. In addition to the Mio Link, they offer more “complete” options for users that don’t want to connect to a watch, or who want additional info. Options like the $149 Mio Fuse include an LCD display and activity tracker. The Mio Link has a 7-10 hour battery life, while the bulkier Mio Alpha has a 20 hour battery life. In my own tests, I got about 8 hours of use per full charge. The sensor itself is very small and lightweight, with most of its size being the battery, I imagine. If you’re interested in the Link, it comes in two sizes (small/medium and large), and two colors (black and white).
After researching and reading reviews of all the different optical heart rate sensors on the market, it’s clear that not all optical HRMs are created equal. While there are at least a dozen watches/HRMs that use optical heart sensors today, many of them are using either Mio or Valencell sensors, most notably the Garmin 225 (Mio) and Scosche (Valencell). Other companies developed their own optical HR sensors in-house.
|Fitbit Surge||Apple Watch - Sport Edition||Mio Link||Basis Peak||Withings Pulse O2|
|Battery Life||7 days without GPS, 5 hours with GPS||18 hours||8 hours||4 days||14 days|
|Heart Rate Monitor||Yes, optical||Yes, optical||Optical||Optical||Optical|
|Waterproof||50 Meters (no swimming)||Splash Resistant||30m||5 meters||No|
|Weight||1.8 oz||1.41 oz||30 g||N/A||N/A|
|Phone Compatibility||Android, iOS, Windows||iOS||Bluetooth Smart (4.0) and ANT+||Android, iOS||Android, iOS|
|ORM Review||Yes||Being Tested||Yes||No||No|
Mio Link Usage
It’s race day, and you’ve just put your sponsor’s temporary tattoo on your chest. After spending most of the morning figuring out which hashtags would be most clever to include in your next instagram post, you realize that it would also be pretty cool to wear a heart rate monitor for the race. But wait! You already have a tattoo on your chest and you wouldn’t want to cover that up. Even if you don’t need your chest to be available for professional reasons, there’s no denying that a HRM on a bare chest looks pretty dumb. You might as well wear nostril openers and prescription eye goggles too. Thank goodness for the Mio Link! In this photo of me at the 2015 Atlanta Battlefrog race, you can’t even tell that I’m wearing a HRM; it’s discretely hidden under my orange wristband.
Not only is it way cooler looking, but also more functional and comfortable. The chest strap has the potential to get in the way of obstacles like bucket/log carries, and cause unwanted chaffing once mud gets stuck underneath the water-soaked strap. After running the 16k Battlefrog with the Mio Link, I’m pleased to say I never even noticed it was on. The wristband / strap is also pretty sturdy and secure, so I never had to adjust it while running (I did, however, have to tuck the strap of my fenix3 back in once or twice).
The Mio Link did allow me to get heart rate data without looking like the data nerd that I am, but the data wasn’t quite perfect. Almost though. After running through dozens of workouts with the Mio, I’ve noticed a few things that cause it to malfunction every once in a while. I’d say 9/10 times, it works without any issues, but cold skin and extremely rapid changes in HR can throw it off sometimes. For this race, it had trouble tracking for the first mile, then worked great besides a brief loss of HR around 33 minutes (due to a water submersion at “mounds of grounds”). The second graph, below, is from a half marathon road race I did the next day, and the Mio performed perfectly. Note that the graph is much smoother for the road race due to the nature of the event, compared to the varying intensity of completing obstacles and navigating trails.
For fairness, the Garmin brand chest strap would also have some difficulty in an obstacle race with water submersions, and possibly additional circumstances that wouldn’t have given the Mio any issues. So, in spite of it having some issues for the first couple of minutes, I don’t consider this to be typical, and don’t imagine a chest strap would be definitively better in an obstacle race environment. After dozens of workouts with the Mio, I found that it has trouble tracking the first few minutes of an activity about 5-10% of the time. This issue can be avoided by connecting the HRM and giving it 5-10 minutes to start tracking your warm up, etc, before actually beginning an activity. Another minor issue I found is that it doesn’t track well on very cold skin. In the summer, this isn’t an issue, but in the winter, it’s best to either wear it extra tight or underneath a sweatband or long sleeve. In general, it works much better if you’ve warmed up first, because of both temperature and additional time to start tracking accurately. Adjusting tightness and position on the arm are both ways that you can try to get a better reading. Thankfully, you don’t generally have to wear it too tight for it work. Just tight enough so that it stays in place is okay, but for an obstacle race I would recommend a tighter fit to keep dirt from getting between your skin and the sensor. A tighter fit in cold weather or rain is also a good way to keep the skin beneath the sensor a little warmer. If you’re wrist looks like this after wearing it, it was probably on too tight:
Mio Link Durability
You probably don’t think of durability issues at all when it comes to heart rate monitors, but the Mio is actually the clear winner in this category. Over time, the elastic band on a chest strap gets over-stretched and worn out, often needing adjustments. Not only that, but it gets sweaty and gross after every workout. I remember leaving my chest strap out in the sun to dry after hard workouts, and washing it by hand with soap when it got especially nasty. I can only imagine how gross a chest strap would be after an OCR. With the Mio Link, simply rinse it under the sink if it gets gross and you’re good to go. That’s it! The only downside to the Mio Link is that you do have to charge it. I get about 8 hours of use per full charge. It is very convenient to charge though, snapping on magnetically to a small usb mount.
- no more annoying chest strap
- connects via Bluetooth and/or ANT+ to pretty much anything
- comfortable, convenient, and works well most of the time
- cost effective
- no maintenance
- water resistant to 30m
- light weight (approximately 30g)
- not quite as accurate as chest strap, especially when high degree of precision is needed, such as for HRV tests.
- battery life / requires more power than a chest strap.
- cold skin, tattoos, poor circulation, and other factors may reduce accuracy.
- no advanced data like vertical oscillation and ground contact time that you get from premium straps
Mio Link Verdict
So you’re probably wondering if I’m going to throw away my chest strap, and the answer is…. I’ll put it on the shelf, but not throw it away. I do like the precision of chest straps for if I want to do an HRV test, and if I want to track heart rate for an event longer than 8 hours then the Mio Link won’t cut it. But, for day to day use, I definitely won’t be using the chest strap. More than anything, I love that the Mio HRM is so convenient that I actually want to track my heart rate for every single workout. It was such as hassle and annoyance having to wear a chest strap that I rarely even used it; now I’ve been tracking HR for every workout for almost a month, and have been able to make use of the data to improve my training. The power of HR training isn’t looking at your HR for a single workout, but tracking it over time, establishing trends and zones, and adjusting your training accordingly. For me, the simplicity of wearing a HRM on my wrist allows me to get the data all the time, and I’m already seeing the benefits. Sure, you may not really be getting data as accurate as from an EKG, but if you’re ready to take your training to the next level and geek out all at the same time, get a device equipped with Mio sensor like the Mio Link or Garmin 225… and leave your chest strap on the shelf.