I used the Polar A370 watch daily for the last two years. It’s a very popular model in the ME HR pacing community, and it has some critical functionality. But I found myself frustrated with data I wish I had access to during the “workout” session.

I recently purchased the Polar M430, and it has a couple of key features that are really missing from the A370. I think it really helps my pacing more.

One challenge in choosing a device, is that it can be hard to anticipate what features you will find useful until you are actually using it. Some folks are able to find used devices on eBay as a less expensive investment while they’re figuring it out.

At the most basic, the feature that everyone wants is a device that alerts you when you exceed your personal maximum heart rate. Both devices do that.

But I also appreciate having context – understanding how I’m doing in the bigger picture of my entire day. The M430 is much better at that.

How I got here

The Polar A370 was my fourth watch, after using two Fitbits and a Mio before it. Those watches were OK when I was periodically checking my heart rate to see how bad my POTS was. But Fitbits in particular, are known for estimating heart rate a bit on the low side. They also tend to round out and disregard spikes, so they diminish POTS episodes. Fitbit also refuses to build in a heart rate alarm. The feature request comment thread is a sight to behold, as users request the feature, and Fitbit never responds.

When I decided to get serious about heart rate pacing, I decided I needed a fairly accurate well-supported device (Mio is not well supported anymore). I know that chest straps are considered more accurate, but I have Fibromyalgia, and can’t tolerate wearing one for an extended period of time. The phone app offerings on Android for chest straps are also much more limited than they are on iPhone. I have a Polar H10 chest strap and wear it occasionally for checks, and used it for the several months that I explored working with morning HRV readings. But it isn’t for me for daily use.

So I was back to watches. The three brands that get good ratings from the ME HR pacing community are Apple, Garmin and Polar. It will be a cold day in hell when I switch to using Apple devices in my life. I’m an Android woman through and through, since the day that the original Droid was released. That left Garmin and Polar.

I was overwhelmed by researching devices back then, because I didn’t understand enough yet. So, I did a moderate amount of research, and decided to go with the Polar A370. It was popular, and I knew I could easily get help from others in my online support groups if I ran into trouble. It was a perfectly good choice. But as I spent more and more time working with pacing, and more and more time with the nuances of that practice, and tracking my data, I wanted more.

The setup needed to run the devices with a vibration alert is exactly the same, and must be done in Polar Flow. The setup for the M430 has an extra step if you want to customize your display, which I tend to think you should want to do

Some thoughts on both devices:

The Polar A370

The A370 is commonly used, so there is a decent amount of information available on it (all things being relative).

The display is dark while your training activity is running. To turn on the display, you need to push the button on the left of the watch. It claims you can illuminate the display with a wrist flick, but I’ve gotten that to work less than 5% of the times I’ve tried it. It does not turn on in response to tapping the screen, like a Fitbit.

Note: The colors in the heart rate numbers are based on my personal heart rate zone settings.

Photo of Polar A370 watch
Photo of Polar A370 watch on a pale arm. The band is white. The display shows a heart rate of 65 bpm in blue. Above that is the time 19:58, which is the amount of time left on the training activity.

Alarm Mode

In these first images, the watch is in the training mode that is started THROUGH THE FAVORITES MENU. You must start the session from the favorites window if you want to use the heart rate alarm. Starting the training activity from “training” in the menu does something else, will I will explain later.

This is what you will see when you turn the display on. The big number, in this example “65” is your current heart rate in beats per minute. The color of the numbers corresponds with the color of the zone that you are in. Blue is the lowest rate that is still in a zone. Numbers that are either so low they aren’t in a zone, or so high they aren’t in a zone, display in white.  You will also notice there is a heart icon, and it too is in blue. The heart icon moves back and forth across the screen to show which zone you are in hierarchically. The left is the lowest, the right is the highest.

Above the heart rate display is a time. For our purposes, this is generally meaningless. Is is not the actual time of day. It is a count down until the end of your workout session. Many of us set our activity workout duration at 20 hours, because we don’t generally run it for longer than that at once. So, in this photo, I’ve been running my 20 hour workout for 2 minutes, and have 19 hours, 58 minutes remaining. I don’t find this useful. And it I wan to know the actual clock time, I have to scroll to another screen. This cannot be customized.

If you scroll down to the next screen section, you see two numbers. The top number, directly below the stopwatch icon, is how long the workout has left. This is also generally meaningless for our use. The lower number, below the clock icon, is the actual time. You cannot change the order of the screens. If you are using this in a training mode all day as I do, you will have to turn on the display, then scroll to the second screen, any time you want to find the current time.

On the third screen, there is a theoretical calorie count.


Photo of watch display showing a bar chart
Photo of A Polar A370 watch display, showing a bar chart in five columns.

Training Mode

If you want any sense at all of how much time you have spent so far in a session in a particular heart rate zone, you cannot also have the alarm feature. And the time spent indicator is a simple bar chart in which you can see relative proportion, but no absolute time.

In order to run the watch in this mode, you begin the activity from the “Training” menu, as opposed to the favorites menu. I know. It makes no sense. I can only tell you that it’s true.







Photo of watch display showing a vertical bar chart and percentages
Photo of an A370 watch display showing post-session details. There is a vertical bar chart, with percentages displayed at the end of each bar.

Post-Session Details

When you finish your training session, you can get a variety of data on your display.

The first information is your MAX heart rate during the session, and your AVERAGE heart rate during the session. These are two data points that I track over time and find helpful to get a bigger picture sense of how I’m doing.

The other information you can access from the watch itself, is a breakdown of what percentage of your time in the training session you spent in each of your heart rate zones. This gives me a bit more of a sense of what I did, after it’s already over.

For the detailed information that includes actual time in each heart rate zone, and the LOW heart rate, you need to sync your device to the PolarFlow app. I developed a habit of doing this every night when I end my session, and reviewing and recording the rest of this data.



⇒The Polar A370 has a moderate vibration when it alerts you, and it vibrates approximately once every 4 seconds until you return to a safe heart rate. To the best of my knowledge, you cannot just “turn off” the vibration which it is alerting, you have to actually get your heart rate back down.

⇒The battery on the A370 does not last very long on a single charge. It seems to depend on how often it vibrates. I can usually get 11-15 hours out of it. Which means it does not always make it until the end of the day.


The Polar M430

Hands down, the only dissatisfaction I’ve had so far:

  • The fit is not ideal for me. My wrist is most narrow right above my wrist bones, so I’ve had to tinker with placement
    or it will slide down too far. With some practice, I have this mostly figured out now.
  • I wish the display was color, because I got used to that in the A370.
  • I had a malfunction that required me to replace the device.

Otherwise, I love this, and wish I’d had it for the last two years. I think I would have paced much better. My top features:

The display is always on. I don’t have to screw around with anything. If I want the display lit, so its easier to read in low light, I just press the upper left button and it lights up. But in regular lighting conditions, I can see it all the time.

Screenshot from Polar Flow app
Screenshot from Polar Flow app shows the screen to edit what is shown on the watch display. This example shows Time of day, heart rate, heart rate zone position, and time in HR zone.
Photo of a Polar M430 watch with time and HR data
Photo of an orange Polar M430 watch. The display shows current time, current heart rate, a slide indicator of current heart rate zone, and  number of hours, minutes, second spent in the current zone.
A photo of a Polar M430 watch showing heart rate and session data
A photo of an orange Polar M430 watch. The display shows average heart rate, max heart rate, and the amount of time spent in the workout session.

The ability to customize what data you display while “training,” and in what combination on which screen is fantastic. This is my current primary screen, what I want to know most often in a quick glance. I chose the current time, my current heart rate, a slide indicator that shows my current heart rate zone, and the number of hours, minutes and seconds I’ve spent in that zone during the session. In this photo, it’s 10:18 pm. My heart rate was 72 bpm. I was in zone 3, which I programmed for 70-76 bpm. I’d spent a total of 4 hours, 58 minutes and 24 seconds in that zone that day by 10:18 pm.

The second screen I chose to display my average heart rate for the day, and my max heart rate so far in each day. These are data points I’ve tracked for the last two years. The time at the bottom is in some ways irrelevant, it is the amount of time I’ve been in the workout session. The reason it is helpful, is that this is the time one would see on the heart rate graph at the end of the day. If I did something specific, and looked at my watch to see how it was affecting me, I could find that same moment later on my graph for the day by knowing the time stamp.


There are a number of other fields to chose from in designing what you want to see on your display.

That’s all pretty great. But what I’m even more excited about, is the ability to see live the number of hours and minutes I have spent in each heart rate zone so far in the training session. The Polar A370 can display a relative graph of this, but not the exact minutes and seconds. AND, the Polar A370 can only show this to you OR activate the heart rate alert vibration. It cannot work in both modes at the same time. This was the single most frustrating feature for me with the A370.

Photo of a Polar M430 watch
Photo of an orange Polar M430 watch. The screen display shows the number of hours and minutes already spent per zone across five heart rate zones.

This display shows in real time, how my time was spent so far. In my case:

Zone 5: 1 hour, 8 minutes, 48 seconds. That zone is anything over my AT, which is 86. The goal is for this number to be as small as I can manage on a given day.

Zone 4: 3 hours, 3 minutes and 33 seconds. That zone is set at 77-86. This zone is better than zone 5,  but I also aim to reduce the time spent here. 86 is my ideal max heart rate for pacing purposes.

Zone 3: 4 hours, 58 minutes, 14 seconds. That zone is set at 70-76. The more time here the better.

Zone 2: 4 hours, 46 minutes, 22 seconds. That zone is set at 50-69. The more time here the better.

Zone 1: I spent zero time in this zone. That is good. I use this zone to see if my medication is dropping my heart rate too low for any period of time.

This data is all visible at the end of the day from either device. But the ability to see it in real time is so great for me.




⇒The Polar M430 has a strong vibration when it alerts you, and it vibrates approximately once every second until you return to a safe heart rate. To the best of my knowledge, you cannot just “turn off” the vibration which it is alerting, you have to actually get your heart rate back down.

⇒The battery lasts a good long while on the M430. I have not fully tested the limits. But it has always lasted a whole day, and I wouldn’t be surprised if it could last a whole sleep session in addition, and maybe the next day.