Wouldn’t it be great if you could record heart rate while training without the need to put on a chest strap? You could say goodbye to placing the moistened strap around your chest on those cold mornings, removing the sweaty strap after workouts, and dealing with the chafing from the strap rubbing the wrong way.
As technology advances, the market has seen an influx of heart rate wrist straps in recent years. As opposed to the technology used in chest straps, these wrist straps rely on optical sensors to measure your heart rate. But how do these wrist straps compare to the tried-and-true chest strap technology?
In this article, I look at the pros and cons of chest straps vs. wrist straps while reviewing one such wrist strap, the Mio Link. I conclude that, although it would certainly be nice to record heart rate while training without the need for a chest strap, the technology is unfortunately still not there.
Chest Straps vs. Wrist Straps
Monitoring your heart rate while training can provide invaluable feedback to both you and your coach. Keeping an eye on your heart rate during your workout provides a way to gauge the intensity at which you’re working. After your workout, logging your heart rate data long with other metrics allows you or your coach to gauge the training effect and to keep tabs on your progress and state of recovery.
Given the value of heart rate training, devices that monitor your heart rate while exercising have typically used a chest strap. The chest strap works much the same way that an EKG machine works in a doctor’s office. It senses the electrical impulses that trigger your heartbeats. Like the EKG machine, the chest strap heart rate monitor does a great job of accurately recording your heart rate.
The wrist strap heart rate monitors use a different method than the chest straps to record heart rate. The wrist straps employ optical sensors to examine the rate of blood flow in the capillaries below the skin. Light is emitted from the underside of the wrist strap into your skin; then a sensor detects how much of that light is returned. In other words, the optical sensor views below the surface of the skin and measures how fast the blood moves past to gain a reading on your heart rate.
The Mio Link
The Mio Link evolved out of the first generation Mio Alpha. The Link represents a slimmed down version of the Alpha at a more affordable price point ($79 MSRP). According to Mio’s website, the Link promises to provide “EKG-accurate heart rate data at performance speeds” so that you can “ditch the chest strap and get accurate heart rate on your wrist.” First, let’s look at how it works; then I’ll discuss how it lives up to its claims.
The Mio Link can be paired with your smart phone via Bluetooth or any training device, such as the Garmin Forerunner 920XT or Fēnix 3, just as you would pair a chest strap via ANT+. In fact, to effectively use the Mio Link you would need to pair it with another device since there are no number readouts on the wrist strap itself.
Although the wrist strap does not give you a digital readout of your heart rate (in contrast to the previous generation Alpha), it does have a small blinking light that changes colors as your heart rate increases or decreases. So, if you learn the color coded system, you could accordingly determine what zone you are in by simply looking at the light on the wrist strap.
Nevertheless, to customize your heart rate zones, you need to download the Mio Go app to your smart phone, and then pair your Mio Link with the phone. Note that your smart phone needs Bluetooth Smart (i.e. Bluetooth 4.0) technology to connect with the wrist strap.
The Good, the Bad and the Ugly
First, the good things about the Mio Link. In addition to the idea of ditching a chest strap for workouts, part of my initial motivation for trying the Mio Link was to find an easy way to check my morning heart rate before getting out of bed, as well as to check orthostatic heart rate (the difference between heart rate while lying and then immediately standing).
Morning heart rate (as well as orthostatic heart rate) provides an important window into your state of recovery and is an important metric to track. As I discuss in a previous article, “If your heart rate is five to ten beats higher than average on a given morning, this is a sign you may need more rest and recovery that day. It could also mean your body is fighting an oncoming virus, in which case eliminating stress in the form of hard training can give your body a chance to nip any sort of oncoming illness in the bud.”
To check morning heart rate, I usually just count my pulse for 30 seconds and multiply by two. But wouldn’t it be nice to simply roll over and scroll to the heart rate screen on your Fēnix 3 or grab your smart phone next to your bed to instantly check that number? Well, I thought so. And it turns out the Mio Link does a good job of accurately providing you with that resting heart rate data.
Upon going to bed, I simply put the Mio Link on my wrist above the Fēnix 3—leaving the Mio Link turned off (otherwise you could wake up with a dead battery). In the morning, I would then turn on the Mio Link and look at my Fēnix 3 to see my resting heart rate. Easy, simple, and it works well. The Mio Link does a good job recording resting heart rate.
However, when it came to using the Mio Link during training, I had abysmal results. To test the accuracy of the wrist strap vs. the traditional chest strap, I wore both on several runs paired to different devices—for example, the Mio Link paired to the Fēnix 3 on one wrist and the Garmin HRM-Run chest strap paired to the 920XT on the other.
Whereas the traditional chest strap gave me data in line with expected results and what I subjectively knew to be accurate, the Mio Link gave me data that jumped all over the place. Over the last half of one long run, the Mio Link gave me an average heart rate of 161 with a max of 201 vs. an average heart rate of 147 with a max of 155 for the chest strap. The chest strap was spot on in terms of my perceived intensity, pace, and type of run—a long run in zone 2. In contrast, the Mio Link had me running at threshold (even though my exertion was nowhere close to that) with a max heart rate well beyond what I’ve done since I was a teenager.
I tried more runs with the Mio Link with no better results. So I must conclude that the Mio Link does not work well for recording heart rate while exercising. And the accuracy is not even close. I fear what would happen if someone new to endurance training who is still learning to subjectively gauge their zones were to rely on a heart rate wrist strap, thinking they were getting accurate feedback. Their training would be incapable of effectively targeting desired training effects at best, and drive them to over train at worst.
So, as much as I would love to ditch the chest strap, I cannot recommend replacing it with a heart rate wrist strap. If you absolutely cannot train with a heart rate chest strap, simply forgo using heart rate. You can use pace or another means to monitor your exertion level instead.
The Bottom Line
The bottom line is that the Mio Link heart rate wrist strap is not a viable replacement for the traditional chest strap while exercising. The optical sensor technology used in such wrist straps cannot match the accuracy of traditional chest straps during activity. However, the Mio Link can be useful for quickly viewing your heart rate at rest, such as in the morning before getting out of bed. The only reason to buy the Mio Link, in my opinion, would be to use it to check morning heart rate. Then again, simply counting your pulse while looking at the second hand on your watch works just as well without the cost. But if you are looking for a way to measure heart rate during exercise without a chest strap, keep looking; the Mio Link is not the solution.
Disclosure statement: The Mio Link tested for this review was purchased independently. The author does not receive any incentive from Mio Global to use its products.