This article covers how to do a Heart Rate Drift Test, using only a GPS watch and a heart rate monitor, plus the heart rate drift calculator on this page to make it easy to know what to do with the result. It also explains why you would want to do a Heart Rate Drift Test in the first place. This is essentially a Zone 2 calculator, because it lets you understand if are you actually running in Zone 2 or not. Note: any references to heart rate zones on this page relate to a 5 Zone model.
- Benefits of the Heart Rate Drift Test
- How to do a Heart Rate Drift Test
- Heart Rate Drift Test Calculator
- What to do with the Results
Benefits of the Heart Rate Drift Test
The traditional ways of measuring your heart rate zones normally involve either Maximum Heart Rate Stress Test or, for those lucky enough to have a lab nearby and the necessary funds, a Lactate Turn Point test. You’d then take the data and apply some splits of Zones based on the outcome. Whilst these do a good job of finding your top end training zones for tempo / threshold runs to get the body to adapt to using lactate as efficiently as possible, they might not be so good at guessing the bottom end for optimal fat-as-fuel adaptions.
A Heart Rate Drift Test instead focuses just on giving you the top of your Z2 / Zone 2 calculation for heart rate so that you can keep your easy runs easy enough (it won’t tell you anything about the higher zones). Much like other heart rate zone boundaries, this will change over time and training. This test does require you to be comfortable with running for 75+ minutes, so if that’s not the case, use the MaxHR Stress Test instead and come back to the Heart Rate Drift Test later in your running journey.
So, what is Heart Rate Drift anyway? During running or other endurance sports, if you keep a constant pace for long enough, your effort / heart rate will normally rise over time, which is the definition of Heart Rate Drift, also known as Cardiovascular Drift (or Cardiac Drift). Conversely, if you keep a constant effort / heart rate, your pace will slow over time. On days where your training plan aim is to train your body to burn fat-as-fuel (easy days, long days), along with all the other benefits of running at an easy effort, you need to know what effort level to use so fat is used optimally. Run too slow and it will be burning fat, but you could have could have been doing more in the time available. Run too hard and it will start using a higher proportion of carbs and lactate as fuel. This optimum zone occurs where your pace at a constant effort is only drifting up slowly, or where your heart rate is only drifting up slowly at a constant pace.
What causes Heart Rate Drift? Heart Rate Drift during exercise is caused by a mix of changes to heart pumping stroke length and dehydration. For reasons not yet known, after a while of exercise, the amount the heart moves in any one pumping stroke reduces, depending on how easy or hard the exercise is. Since the amount of blood pumped in any one stroke is reduced, to keep the same level of oxygen supply, the heart rate must increase (drift upwards). Additionally, during exercise the body temperature heats up, blood is diverted nearer the skin and sweating increases. As fluids are lost, blood pressure drops, so again heart rate has to increase to compensate. This latter reason can be managed by good hydration in the 24hrs leading up to the exercise and if it’s a longer session, replacing lost fluid too.
The Heart Rate Drift Test shown here lets you spot the amount of drift and adjust accordingly in following training. If you run at a constant heart rate for an hour, you’d expect to travel further in the first half hour than the second half hour. Comparing the two halves shows you how much drift there is at that heart rate. This might seem odd to test this way around – we are checking for pace drift really – but if we are trying to train without going outside of Zone 2, then keeping to a constant pace and letting the heart rate drift upwards (eventually into Zone 3) isn’t going to work. So the test protocol on this page simulates more closely what you’d be doing in your long runs if you were trying to stay in Zone 2.
Does it matter which way round you test? Possibly not – my results are the same whether I check for pace drift at constant HR, or heart rate drift at constant pace. However, in real life, unless you have access to a treadmill, I think it’s easier to run at constant HR – real time pace readouts on sports watches are pretty poor and easily affected by tree cover and buildings.
A note about heat: on very hot days, pace will drift much faster at a set heart rate. You may get a very high % drift if you test on a hot day, which might be a bit misleading to your general training because if you tried to reduce pace enough so the HR doesn’t drift, you might be almost walking – this will still give adaptations for aerobic fitness, but you’ll lose ability to actually run! So if it’s hot, make sure some of your easy training days are still using the legs for running, perhaps by alternating running and walking instead of trying to stay in some middle-ground shuffle.
How to do a Heart Rate Drift Test
You’ll need:
- An accurate GPS device that can record your distance over time, or a treadmill.
- An accurate heart rate monitor.
- Somewhere suitable to do the test.
- A guess of your target heart rate.
- The calculator on this page.
GPS Device: An accurate GPS device would normally be a GPS watch, but you could use a phone with an app that records your runs if it’s easy to start and stop activities at exact times.
Heart rate Monitor: To get an accurate heart rate, you’d normally wear a chest strap heart rate monitor during the heart rate drift test. At low efforts, if worn correctly, a wrist based monitor (in a watch) can be fairly accurate, but it’s easy to wear them wrongly so that the heart rate is too high while running. That link will explain how to get better results with a wrist based heart rate monitor.
Somewhere to run: If you don’t have access to a treadmill, to perform the heart rate drift test, you’ll need to warm up and then run somewhere for an hour. A suitable place to do the test would be somewhere fairly flat. Somewhere with long straights, few corners, low buildings and few trees will give better GPS data for distance, so not a running track which will show a different value each lap. Also avoid change in wind direction (or use a calm day). The test is split in two halves, over an hour, so if one half was on the flat and the other half hilly, or one half wind in front and other behind, the results would be invalid. Aim to be close to home after the allotted time.
Target heart rate: Since the whole point of the heart rate drift test is to test a given heart rate to see if your pace only drifts a little, you’ll need a value to aim at the first time. Perhaps you know there’s a heart rate that you feel like you could run at for a couple of hours and it would be quite easy. Or if your training runs are currently a lot shorter, what’s your heart rate at an effort level where you can “Say a sentence of about this length while running, without gasping for breath in the middle“? Or if you’ve already set heart rate zones based off another test (such as the Runningversity heart rate zone calculator), start with the top of Zone2/Z2 heart rate. Failing those, do 180 minus your age; it’s incredibly generic, but will give you a starting point.
Test Protocol Summary
- 15 minute super gradual warm up to target heart rate
- 30 minute run (new activity recording, or new lap)
- 30 minute run (new activity recording, or new lap)
Total: 75 minutes.
Warm up – 15 minutes: When you are ready to do the test, do a warm up run. Run very slowly to start with and gradually let your heart rate rise to your target heart rate after ten minutes and check it holds there for another 5 minutes – slow down if need be so that it stabilises. Without stopping running, start a new activity recording on your GPS device – if you were recording the warm up, stop / save it and start a new activity recording. If your device’s phone or browser app lets you see “average HR” and distance data by lap afterwards, then you can press the lap button instead, as long as it’s not also doing auto-laps by mile / km. If in doubt, the stop / save / start method is fine.
30 minute run – First half: Keeping your heart rate a close as possible to your chosen target, run for 30 minutes. Since you’ll be glancing at the heart rate value on your device regularly, remember to also maintain your running form. At as close to 30 minutes as possible, stop / save the recording, but keep running! Start a new activity recording on your GPS device. Or again, use the lap feature, given the caveats above. Don’t worry if you press stop / save a few seconds before or after the 30 minute mark – you can enter the exact minutes and seconds into the calculator and it will adjust accordingly.
30 minute run – Second half: Continue running for another 30 minutes. At as close to 30 minutes as possible, stop / save the new recording.
Head home and plug the results into the calculator below.
Heart Rate Drift Test Calculator
Calculate your Percentage Drift from your Heart Rate Drift Test data:
What to do with the results of your test
The calculator above will show you your % Drift during the test. It also then tells you what to do.
<0%: Something is wrong! Given a constant heart rate, you should have travelled further in the first half hour than the second half hour, but a value less than zero (negative) suggests the opposite. Did you mix up the results of the first and second half?
0-3.5%: You are definitely running at an effort that burns mostly fat as fuel, but you could raise the effort a little to get more done in the time available to you. Come back here and test again next week with a heart rate a few BPM (beats per minute) higher.
3.5-5%: You nailed it. You can use your target heart rate for this test as the top of your Zone2/Z2 for future easy / long training runs if the aim is to train for fat burning adaptations. Come back here and test again in a few months.
>5%: Your effort level / heart rate was too high. Come back here and test again next week with a heart rate a few BPM lower, repeating until you get a more gradual drift in the 3.5-5% area.
Hi everyone. I’ve updated the drift test calculator to include minutes and seconds fields for each half so that you don’t have to press stop / save at exactly 30 minutes – if it’s for example 30 minutes and 25 seconds, the calculator will adjust accordingly.
For me it would be easier to run the same distance in each section of the test. For example, run 5 km in 30 minutes, measure the average heart rate, and immediately run another 5 km in 30 minutes and measure the average heart rate. Would the test still be valid?
Hi Manuel, yes the test would still be valid – you’d expect your heart rate to have drifted higher in the second 30 minutes. The calculator takes this into account. If you have access to a treadmill, this is a good option.
Hi, Thanks so much for the detailed test description and calculator. I was looking for an alternative to the Uphill Athlete method so I could calculate without a Training Peaks subscription. This is so helpful! There is something in your description of the zones which I’m confused by however.
When you say the Aerobic threshold is top of Zone 2, are you referring to the same zone system that your zone calculator uses? (i.e. LT is towards the top of zone 4).
If so, I’m confused, as I thought that AeT would be top of zone 3 in your system (not top of zone 2).
Uphill athlete ( who I think popularised this test) seem to use different zones to many systems and I wonder if this leads to confusion. They have the LT at top of zone 3 (making AeT the top of their zone 2).
Any help appreciated!
A confused runner.
Hi Robert. Thanks, I’ve added a note at the top of the page to clarify that I only refer to a 5 Zone model. Aerobic threshold for me is an effort at which you could go a long time without your HR drifting up much, i.e. somewhere in Z2 in a 5 Zone model – but it doesn’t have to be exactly at the very top of the Zone because people shouldn’t fixate on exact bpms – rather aerobic threshold is somewhere near the top of Z2. The the drift test on this page guides you towards it. You’d be mostly burning fat as fuel. If you increase the effort, proportion of sugars as fuel increases / proportion of fat as fuel decreases, and you’d be producing / using more lactate through Z3 and on into Z4. Somewhere *within* Z4 (but not necessarily at the top of Z4), you’d reach lactate threshold – see my lactic acid article to understand how to determine this without a lab test – a point at which your body can’t use lactate as quickly as it is producing it. Don’t fixate on the zone boundaries as much. The heart rates for aerobic threshold and lactate threshold move around a bit depending on conditions, so keeping within Z2 and Z4 respectively guides you towards the right effort level, and then listening to your body does the rest. Hope that helps.
I’m not sure why you got the impression AeT would be at the top of Z3, so if you could clarify what made you think that, I’ll make edits accordingly 🙂
(Z1 very easy, Z2 easy with aerobic threshold somewhere near the top of it, Z3 Marathon effort, Z4 with lactate threshold somewhere within it, z5 v02max)
I did two tests two days in a row – the first was at 140-141 BPM, and the next day, I did the test at 150-151 bpm. On the 140BPM test, I drifted 6.4%. Interestingly, I drifted less on the 150bpm test – only 3.6%. What should I do with this information? I was actually more well rested and better fueled going into the 140bpm test. I did them at the same time of day and in the same weather, too.
That’s pretty odd. How confident are you in the data? Does the HR bounce around or did it stay the same the whole way? And why did you decide to run at a higher HR on the second day?
The HR remains mostly the same for both tests, only ever drifting 2-3 bpm above or below the target. In terms of effort, the 150bpm test was also slightly harder than the 140 bpm text, which is to expected. Is it possible for aerobic threshold to physically shift in the HR range day to day? Maybe the day of the 140bpm test I had poor sleep quality without realizing, that sort of thing – causing it to go lower. The reason I decided to run at a higher HR the next day was because of before I found out about HR drift tests. Previously, to find my zone 2 I used things like the talk test and the nose breathing test – these put my threshold around 160-165 bpm, because I can comfortably talk around that pace. However, I still found myself with fatigue and burnout, and my zone 2 pace was getting worse with time (I have examined other factors like sleep, to be clear). When I did the 140 bpm test and drifted too much, my pride said “no way my threshold is this slow/low in the HR range, right?” and so I did another test the next day. I don’t have access to a treadmill, so I had to do this on a flat, long loop – maybe slight GPS discrepancies were enough to screw things up? I did notice within the calculator that small changes as little as .1 miles difference could cause my drift to change from below 5% to above 5% and vice versa. Regardless, it doesn’t explain the original issue, and clearly my aerobic threshold is still significantly lower than I thought it was. What I want to know is, should I play it extra safe, and sit around 140bpm for my zone 2 runs, or if my threshold really is 150, would I be leaving big gains in the tank by doing that?
.1 miles is quite a long way. At base pace, it would take a significant time to run that. Which is why the test needs to be with a watch that does two decimal places.
Are you using a chest strap? If not, maybe borrow or buy one to be sure of your data.
You could always try the normal MaxHR Stress Test and resting heart rate to get your HRR and equivalent zones, because the drift result shouldn’t be wildly different.
the watch I have measures to the hundredth, I just used .1 to mess around with the calculator. Obviously thats a big difference in time, but in terms of percent difference between two runs of 5+ miles, thats less than 2% difference. I am using a chest strap. The reason I used a drift test is because I found that other tests, such as MaxHR, talk test, nose breathing test, or maffetone calculations were all giving me incredibly different results, all seeming to be too high. I would build up fatigue very fast, and they placed my zone 2 HR somewhat close to my maximum (80-82%). It seems to me to be a matter of fatigue. Since the original tests I’ve noticed on days where I am more well rested I can safely run at 147-150bpm and not drift that much, but if I am very tired or running low on sleep I need to sit closer to 138-140 or I start to seriously drift upward.
Hi, this is a follow up comment. I have been doing some zone 2 training for a while and these two original tests are not a fluke. The highest I can push my starting HR for these drift tests and still be considered aerobic is around 158. Regardless, I got curious and had done another more at 140bpm and 150bpm and I still drift more at 140. In fact, to remove the possibility that I was more fatigued for the 140bpm test vs the 150bpm test, I just did an experiment today. For my long run, I did two HR drift tests, one after the other. I did my warmup, stabilized my HR at 140bpm, and held my pace at a constant 10:20 per mile. For the 140 test, I drifted to 149bpm for the hour, or 6%. This is the same as before, and implies that I was above my LT1. Seeing as my HR for the end of my first test was so close to the starting HR for the 150 test, I kept running and immediately picked up my pace to 9:25 per mile, and held constant(was within 2 seconds either side for the remaining miles) for the next hour. For the 150bpm test. I drifted to 155bpm, which is a 3.2% drift. I drifted less, at a significantly faster pace – immediately after performing the first test. This makes virtually no sense. I was in a pre-fatigued state. In addition, the second test physically felt more difficult than the first, which makes sense seeing that my HR was in fact higher. My HR was pretty stable the whole way and did not bounce around. The ground I was on is extremely flat and the same material for essentially the whole trail.
Are there any studies or research papers that compare results from the heart rate drift test and lab testing? I was hoping to see some research validating the heart rate drift method, but I was unable to find anything on the topic
Good question. Not that I know of. In my experience, it correlates close to an effort I can sustain all day but still feel I’m running nicely, better than the arbitrary cutting up of the 5 Zone HRR model into 10% slices once you get down to Z2, and should still prevent people from running too fast on their easy days. I still run below the drift tested cap much of the time, but it gives a bit extra to play with for most people. And if people haven’t bothered to do a maxHR stress test and check their resting HR, then the drift test will give a more useful result than whatever else they are guessing with for Z2.
Hi. I got a strange result. Im 28 years old.
My first attemp i did 154bpm and got a drift of 7.5%.
This time (a week later) i tried 151bpm and got 13% drift!
Could it be caused by the heat? I used a wrist monitor, but it seemed to be precise
It could be a number of things. It could be heat. You could be getting ill. Poor sleep quality. Tough training this last week. How did it actually feel?
Heat does make a huge difference and when it’s hot, you have to some days run even easier and some days just ignore it and go high heart rate so that the legs get a normal workout.
I’ll add some notes about heat to the text.
Hi and thanks for the simple tool! Not only did I do my fastest 10km ever, but I did it with 3.4% drift so I know I can run faster! However, I did this test on holiday at 150masl, but I live and race at 1000masl (where there isn’t anywhere flat). How should I modify the result to define the top of my Zone 2 at home? Thanks!
Were you just jogging round the 10K? It would be highly unusual to get only 3.4% drift in a fast 10K, regardless of sea level. Anyway, to answer your question, higher altitude means lower pace for any given heart rate, so you’ll have to slow down a bit. However, 1000masl isn’t very high, so you may not notice much difference. You mention it’s not flat though, so this makes it tricky since you have to go slower on the uphills and can run faster on the downhills (for any given heart rate). You might find that trying to stick to heart rate on the way up means only walking fast, so you miss out on running. So your options are to do dedicated high heart rate hill days. Or on easy days you can do mixes of running and walking to get the heart rate back down again. Hope that makes sense.
So once I find my aet, should I train right at it or below it? And if below by how much?
Thanks!
A bit of both! If it’s a long run, you can either train to heart rate, so your pace slows throughout the run, or you can start at a lower heart rate keeping a similar pace and let the heart rate rise throughout – good to mix these up. On shorter runs, you might run at it, but ultimately, sticking to rigid rules like that don’t help you. Think about your recovery level – if you are feeling amazing, then run at it. If your legs are feeling it a bit from the previous day, or you are tired from lack of sleep, then run below it. You can run in Z1 if you want. Always listen to your body first for best advice 🙂 Hope that helps.
So what you’re saying is as long as you’re recovered well, you get more benefit from running at the top of zone 2?
Thanks!
Correct. Better adaptation response to training stimulae. But always consider a lower intensity as optimal training too if recovery requires it. 🙂
My heart rate is much higher than expected (low-mid 160’s) for zone 2 but I got 4% drift. Max hr is ~195. Should I really aim for hr in the low 160’s or somewhere between that and ~70% max hr (high 130’s)?
Roughly how old are you? What’s your resting heart rate? And how confident are you in the data during the drift test (for example, was it a chest strap or a wrist monitor)?
Thank you for this great tool!
It allows me to control my Training in a very robust way without spending a lot of money on expensive labs!
Glad you are finding it useful. 🙂
thanks for your article.
could you give us the detail of the computation to bring some more insights of the concept of drift ?
Hi Tom. It’s really simple. It just compares the delta of first half to second half as a percent change. If the percent change is large, then the effort level won’t be sustainable and will push the heart rate into Z3 before the end of a long run. In Z3, adaptations for burning fat as fuel will be minimal, with majority coming from glycogen. All the other adaptations from running slowly will be less effective too. https://runningversity.com/why-run-slow-to-run-fast/ (copy paste that or press the search button and look for “run slow” to see the article that explains all the reasons a good chunk of your runs should be slow).
So is the second half avg heart rate the top of your Z 2, or the first half? My first half was 139 and second half was 145 running 4 miles each.
Hi Adam. I’m guessing you had the same pace in both halves, rather than trying to keep the heart rate stable. In your case, if the test comes out within ~0-5%, then you only have a small amount of drift and are unlikely to drift into Z3 in a normal-length training run if you have a heart rate of 139 in the early stages. 145 is also in Z2, but probably not the top and you’d be able to another hour without it rising too much. If you do one again in a few weeks, try to keep the heart rate stable, which will mean slowing your pace (as per suggested test protocol). Hope that makes sense!
Great tool! I used this on the stationary bike, probably much easier than running and checking heart rate, and it also lets me have my water quickly at hand. I nailed it on the first try.
Oooo, interesting idea! Cheers.
Hello there, is the distance required for the calculation in Km or Miles?
In Km I’m below, at 3.3%. Miles seems to be spot on with 3.6%.
I would assume I’ve found the threshold? Anyway, curious about the above.
And thank you so much for providing the calculator for free ???
Cheers,
Be
Hi Ben. It’s a ratio of the numbers, so as long as the unit is the same in both halves, it doesn’t matter if you use KM or Miles. The reason they come out slightly differently in the calculation is the conversion Miles <> KM (either on your watch app or whatever you used). I’ve changed a bit of the wording on the calculator to make that clearer. And yes, that result seems a good starting point for you. Come back and try again in a few months in case it has changed 🙂 Glad you found it useful. Tell all your friends, share etc.
Thanks so much for the prompt reply!! 🙂
Will use this for a start and test again in a few, as you’ve suggested.
Cheers!
Ben
Is the HR coded backwards in the calculator? I entered a faster HR on the second half, but it calculated this as negative drift.
First half: 4.49 at 144 BPM
Second half: 4.49 at 147 BPM
Result: -2% drift
Hi Aaron, you might be right. I’ll check. I could swear it was working before. Thanks for letting me know.
EDIT: Ok, the calculations didn’t account for people running the same distance and letting the HR drift up – my guidelines above expect the distance to decrease and the HR to remain the same (really distance drift) because it’s easier to maintain HR on slight inclines than trying to keep pace steady and other reasons. Anyway, I’ve modified the calcs to include letting the HR drift and keeping the distance the same. It will also now throw an error message if the second half is easier than the first half. Cheers for pointing it out.
Wow, thanks for going the extra mile maintaining this calculator! I’ve seen the HRD test recommended by a few guides, but this is the only calculator I’ve seen that accounts for both HR and pace.
Funny enough—I meant to keep a steady HR, but was wasn’t precise enough. This was a trail run, and it’s a total coincidence that the two halves were nearly equal.
Thanks again and happy trails!