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.
- 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 MaxHR 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/Zone2 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 this 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 plain aim is to train your body to burn fat-as-fuel (easy days, long days), 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 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 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 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.
How to do a Heart Rate Drift Test
- An accurate GPS device that can record your distance over time.
- 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: 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 of another test, or even your age, 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)
- 30 minute run (new activity recording)
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 one).
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 exactly 30:00 minutes as possible, stop/save the recording, but keep running! Start a new activity recording on your GPS device.
30 minute run – Second half: Continue running for another 30 minutes. At as close to exactly 30:00 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 and 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.
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