Can You Trust Your Running Watch?

How much do you rely on the data from your running watch? Do you analyze all the data it gives you after every run?

In this Run to the Top episode, we’re going to take an in-depth look at how much you should trust this data and how you can most effectively use it in all training situations.

In this episode, you’ll learn…

some of the great features that make your watch more useful
how to use it more effectively in workouts and on the treadmill, and
how much to trust all those fancy assumptions and predictions your watch is telling you.

Whether you’re a running data geek or you barely know how to use your running watch, this episode will definitely give you some practical training tips.

I would bet most runners consider their running watch just as essential to their training as their shoes. Sure, there are plenty of people that couldn’t care less about recording, analyzing, or god-forbid sharing their runs with other people on an app. For them, running is not about data or distance or anything that can be reduced to zeros and ones on a screen.

But this episode is not for them.

On today’s Run to the Top Podcast, I’m going to take a look at your running watch. We’ll explore:

some of the great features that make your watch more useful
how to use it more effectively in workouts and on the treadmill, and
how much to trust all those fancy assumptions and predictions your watch is telling you.

I’ll be mostly using Garmin as an example since that is what I own and what the majority of runners use, but this is applicable to any watch that is meant for running.

The most basic reasons for having a running watch is to be able to tell how far you went and how fast you were going. Before GPS watches, most runners did that by driving the route in their cars or memorizing a map and using the stopwatch function on their simple Casios. Then they’d have to do some math and use a paper training log to record it all down to measure their progress.

We’ve come a long way since the first digital watch days. Today’s high performance watches from brands like Garmin, Coros, Fitbit, Suunto, and yes, even Casio can not only track how far and fast you ran, but they can tell you other running metrics like stride length, heart rate, vertical oscillation, power, cadence, and more. The technology also claims to be predictive, using algorithms to estimate recovery time, your VO2 Max, predict future race finish times, tell you if you are peaking, overreaching, or undertraining.

It’s like having a running lab and a running coach on your wrist at all times. Or is it?

Just how accurate and useful is all this information? I’ll get into that in just a minute, but first I want to go over some simple ways to use your watch as the amazing tool that it is. Because if you are only using the start and stop button for your runs, you’re missing out on some really cool stuff that can help your training.

The first thing I tell all my athletes to do is get to know the lap button. On a Garmin, it’s also the back button, located on the bottom right corner of your watch. Normally, your watch should default to auto-lap, which means that it will tell you your pace per mile or per kilometer, whatever you set it up for initially. This is perfect for easy runs or for runs where you only care about your pace per mile or kilometer. But for any other run where you are trying to change paces in a different distance, you’ll want to use your lap button.

So let’s say, for example, you have a workout that is 5 repeats of 800 meters. You start your watch and do your warm up. When it’s time to speed up for the intervals, hit the lap button. Your watch will remain running, but you’ll see a lap time start at zero. Run your interval and then hit the lap button again for your rest period. Again, the lap time will clear and you can see how fast (or slow) you are jogging your rest period. Then hit it again when you begin your next repeat and so on.

If you were to simply keep your watch running, you would not be able to split out your paces for the intervals and the rests.

Your other choice is to stop and start your watch whenever you change paces. This will do the job, but it will create a separate run log for each part, and in this example, that would be 12 logs for one run, which is a mess for you and your coach if you have one. And you’ll usually be standing around waiting to catch the GPS signal each time, which not only breaks up your workout, but it’s super annoying.

Now if this is all you learn about your watch today and you do nothing else, this is in my opinion the most important thing. But it does require that you memorize your workout or write it on your hand, which is less than ideal if it’s a complicated run.

To solve this problem, you can create a workout ahead of time and push it to your watch. When you start the run, your instructions are there for you and the button pushing is unnecessary. Each brand will likely have a slightly different way of doing this, but many athletes find this feature very helpful. After all, when you are running hard, you need all your brain power focused on your run, and not on trying to remember your workouts.

If you’ve ever run with your watch on the treadmill, I bet you’ve noticed that what your watch says never matches what the machine says. This happens for several reasons and my best advice is to accept that it will never match and try to be okay with that! The first thing you want to check is that your watch is on Indoor Mode and your GPS isn’t running. Running in place tends to confuse GPS, so you are going to be more accurate without it on the treadmill.

If you are on your machine at home, check with the manufacturer about how to ensure that it’s calibrated correctly. You might be able to make some adjustments that will help. But if it’s a machine at the gym, you’re not likely going to be able to do much about it.

Personally, I like to use my watch on the treadmill and I just go with whichever one tells me I’m faster.

Alright, now that we know not to expect perfect accuracy inside, surely we can trust our watch for pace and distance outside right? Well, not so fast.

When you are running outside, your GPS watch does a far superior job than your cell phone can at estimating how fast and far you are going. But hills, trees, skyscrapers, turns, and running with 50,000 people who are all trying to access the same satellites at the same time will all negatively affect GPS accuracy. And unfortunately, it typically overestimates the distance you’ve run. So if you’ve ever been upset when your watch hit 26.2 miles and you still have a quarter mile of the marathon to go, now you know why.

There are a lot of bells and whistles on modern watches and I won’t be able to get to all of those today. You might love all the features or never even use them, but it’s good to check out your manual because if you wish that your watch could do something a little differently on your run, there’s a good chance that it can.

Now I want to get into all the predictive features on your watch. You know, those notifications that pop up and tell you how you are performing or how much recovery time you need. Are those really accurate? Is your Garmin secretly judging you?

I don’t know about you, but sometimes I feel like my Garmin is being way too “judgy” with me. I’ll be out for a nice, easy run after a rest day, feeling great and then up pops a notification that I’m being unproductive. Oh really, Garmin?! That is a little presumptuous and kind of mean, isn’t it?

According to Garmin, it measures your training status by calculating “several dimensions of your personal physiology. It considers changes in fitness level (your VO2 max), your current acute (7-day) training load and any change in your longer-term training load, giving you guidance to help you improve your training decisions.”

That all sounds great, of course, but my watch really doesn’t have a clue what I’m training for (or not training for), what I’m doing long term, and where I am in my training cycles. And for me personally, I take my watch off when I’m not running, so it only knows a tiny bit about my overall physiology.

In other words, it makes assumptions about whether you are peaking, productive, maintaining, detraining, or overreaching without all the facts. It doesn’t ask you how you feel, how your day at work was, if you had a fight with your spouse, what you’ve been eating lately, if you’ve been meditating, etc.

Now, those notifications could be helpful as a quick reminder to make sure that I’m on track with my training plan, but other than that, I will always question those judgments. If you are concerned, that’s where a good coach can help, far more than an algorithm.

But what about VO2Max? Maybe my watch can estimate that based on what I’ve been running lately.

Simply defined, Vo2 max is a measure of the maximum amount of oxygen your body can utilize during exercise. The higher it is, the faster you should be able to run aerobically (for the most part), so it’s a great number to measure increasing or decreasing fitness. Scientists measure this number in a lab, hooking you up to machines that measure each breath while you run on a treadmill. Can a little sensor on your wrist really do the same thing?

Garmin claims it can. It “reliably estimates your VO2 max by identifying, analyzing and interpreting meaningful performance data during your run. The pace you are running is placed into the context of how hard your body is working to produce your performance.”

In other words, it looks at how fast your heart rate is {Heart Beat sound under this:} beating with the speed that you are going after adjusting for terrain. Then it takes a look at your age, your gender, your history and your recent runs and gives you a number.

How does your watch’s estimate compare to a lab result? Well, for Garmin, at least, it’s pretty darn close. Their own testing showed that it’s accurate within 5% and subsequent independent tests have shown even smaller inaccuracies.

But one factor that nearly doubled the inaccuracies was a misestimation of your maximal heart rate. You know that old equation that your max heart rate is 220 minus your age? Well, that just doesn’t fit for a lot of people, especially trained athletes who work hard and get their heart pumping. If that’s the case for you, your watch’s VO2 max estimate can be off by as much as 9%.

So instead of thinking of that number as an absolute, use it to watch for trends. If one day your VO2 max shoots up 5 points, that could mean you are getting fitter. But if it drops, that doesn’t always mean you are not, so take it with a grain of salt.

How about things like recovery time and training load? How does Garmin judge those? I don’t know if this has happened to you, but I’ve come back from a normal, gentle run and my watch will claim that I need to lie on the couch for 3 days to recover.

Surely, that can’t be true, right? It’s not. Remember how I said earlier that I take my watch off when I’m not running? I have very sensitive skin and I can’t wear the thing all the time. Turns out, that practice is affecting Garmin’s predictions. It doesn’t know my sleep patterns, resting heart rate, steps I take during the day, or anything else about me. And more importantly, it will fail to capture my EPOC data.

EPOC is an acronym for Excess Post-Exercise Oxygen Consumption. This is a measure of how hard your body has to work to put yourself back to equilibrium after training. Of course, your watch isn’t actually able to measure your oxygen consumption. It takes an educated guess based on your heart rate and everything else it knows about you.

Even if you do wear your watch 24/7, it can only provide a rough guess of what your body is going through on a daily basis. So again, take a peek at these metrics for trends, but they aren’t gospel.

Finally, how accurate are those race finish time predictions? You know the one that says you can run a half marathon in x and a marathon in y? Those estimations are probably the worst. I know for sure it’s completely wrong about me personally since I skew faster for the marathon and relatively slower as the distances shorten.

But I also found an interesting story about one runner who trained with both a Garmin and a Polar at the same time. The predictions each made about his race times were alarmingly awful with about a 20 minute difference in his half marathon estimates. Of course, this is only the experience of one guy, but it is an example of how you can’t depend on your watch to predict the future.

With all the mathematical models and machine learning, we might expect our watches to keep getting better at learning who we are and what we need. But for now, I think on the predictive features at least, they are “overreaching”. Or maybe they’re “unproductive.” If anything, they are certainly not “peaking” and have room to reach their full potential. I know, I know, I’m being judgy, but it takes one to know one, right?

Overall, modern running watches are awesome and they are fantastic tools. No, they are not perfectly accurate at anything that they measure, but it sure beats measuring your routes with your car and using a stopwatch.

When it comes to what you need for your training, you can’t delegate that to your wearable. A good coach can help immensely, but learning to understand your own body is the ultimate goal.