Pinpointing your Aerobic Threshold (AeT) heart rate is the first step in setting up your training intensity zones. These zones will help direct your training to ensure the development of a strong aerobic base. While the gold standard for measuring it would be a laboratory test, the following Aerobic Threshold outdoor test works well for most (around 70 percent of) people when it comes to determining a baseline for aerobic training. If you have access to a treadmill, consider doing an indoor variation of this test: Read the eight-step instructions for determining your AeT on a treadmill.

You’ll want to do this AeT test in a fasted state. This means no food of any kind for at least 2 hours before the test.

Aerobic Threshold Outdoor Test

An outdoor uphill hike/run Aerobic Threshold test is not as controlled as a treadmill test, but it can still set a great baseline for your AeT. For this test the most important part is keeping a steady heart rate for as long as possible. We recommend using a long, gradual hill in the range of 5–10 percent grade, but if you only have a flat area you can make this work too.

You will need a heart rate monitor for this five-step outdoor AeT test.

1. 1. Make sure your heart rate monitor is working.
   2. Do a walking or slow running warm-up for 15 minutes or until you break a sweat. Make sure it is low intensity.
   3. After this warm-up, but without stopping, begin to increase heart rate gradually—5 bpm every 3 minutes—while breathing through the nose only.
   4. When nose breathing becomes too difficult, back off just enough to a sustainable nose breathing pace for 10–15 minutes. Note your heart rate at this pace! There is usually only a 2–4 bpm difference between easy breathing and unsustainable nose breathing.
   5. The average heart rate you see in these 15 minutes is your AeT heart rate and will be the guide to the top end of your aerobic zone (Zone 2) for the next 6–10 weeks.

Some folks have trouble breathing through their nose. This AeT intensity we are looking for also corresponds quite well to the point at which you can no longer carry on a conversation by speaking in full, normal sentences.

We have also noticed that those athletes suffering from severe Aerobic Deficiency Syndrome will be able to nose-breathe or converse well above Aerobic Threshold. For them we recommend the heart rate drift test.

Side Notes

As your aerobic system becomes more powerful, you will notice that your AeT heart rate and pace will both increase over time. These increases will be small increments and will continue to accumulate over many months of consistent training. In the long term, this AeT (aerobic capacity) can continue to improve for years and years with proper training. If for some reason you have spent a lot of time at high intensity while nose breathing, you may need to do a more precise lab test to determine your aerobic baseline.

If you live in a town or don’t have access to appropriate terrain, see our Indoor DIY Guide to Determining Your Aerobic Threshold for how to do a self-administered AeT test on a treadmill.

For a full rundown of Uphill Athlete’s recommended methods for determining AeT and AnT (Anaerobic Threshold), read “Aerobic Self-Assessment for Mountain Athletes.”