How To Measure HR Zones

Using heart rate (HR) to determine intensity is the best way to set our training sessions and maximise the benefits of training. While there are a few different models for HR zones, most of them are very similar and just use slightly different terminology. However the recommendation of how to determine an individual person's HR zones is varied and there are many generic calculations, such as using percentages of estimated maximal HR, that are inaccurate. This simple 4-zone system does a good job of personalising intensities to your unique metabolic response by anchoring this system to two important metabolic markers (AeT and AnT).

Basics of Exercise Physiology

We have 2 main energy systems that generate energy, they don't work in isolation but one will be working more than the other depending on intensity.
The aerobic system uses oxygen in a chemical reaction to create energy without by-products like lactic acid that slow us down, BUT it takes time to do this.
The anaerobic system doesn’t use oxygen and so it can generate energy faster allowing us to go faster, BUT it has by-products like lactic acid that slow us down.
If we are exercising at a low intensity and have sufficient time to use oxygen then we will use the aerobic system. As the intensity increases, the percentage of energy provided by the anaerobic system increases. Eventually it is nearly 100% anaerobic and we are producing too much lactic acid and have to slow down. Think of a bathtub filling up with water faster than it can drain and it eventually overflows.

Not only does the aerobic system not create by products, it also helps to “ mop up” the overflowing lactic acid and reuse it to create more energy (this is why the aerobic system is so important!)
Our AeT is the point of 2mmol of lactate in the blood and is when we start using more of the anaerobic system
Our AnT is the point of 4 mmol of lactic acid in the blood and is when we are creating more lactic acid than we can get rid of and can only sustain this level of intensity for a short time.
Aerobic Deficiency Syndrome ( ADS) is when the difference in HR of the AeT and AnT is >5-10%. (Eg an AeT=150bmp and a AnT =180bmp has a 17% difference)

Heart Rate Zones

Zone 1:

HR=: Aet-20%-AeT-10%
Perceived effort: very easy to easy
Purpose: Aerobic conditioning
Method: continuous 30 minutes to several hours

Zone 2:

HR: AeT-10%-AeT
Perceived effort: moderate for those with a high AeT, easy for those with a low AeT
Purpose: Aerobic capacity, muscle economy
Method: continuous 30-90 minutes

Zone 3:

HR: AeT to AnT
Perceived effort: medium, fun hard, not exhausting
Purpose: aerobic capacity, anaerobic capacity, lactic acid clearance, muscle economy
Method: interval 10-20 minute reps or continuous up to 60 minutes

Zone 4:

HR: AnT to Max HR
Perceived effort: hard, Max sustainable
Purpose: maximal anaerobic power, strength/speed endurance, muscle economy
Method:intervals 30 seconds -8 minutes

AeT Test

Equipment needed: HR monitor ( not wrist based) and either; a treadmill or a flat track/running loop AND a GPS enabled watch
Step 1: Estimate what you think your AeT might be, then do a 15 minute warm up building up to the pace that correlates with that HR. This pace should feel easy and like you could breathe through your nose only.
Step 2: Start the test: maintain the pace you have found that initially matches your estimated AeT, do not deviate from this pace, go for 1 hour, press the lap marker on your watch at 30 minutes.
Step 3: As this is a submaximal test you shouldn’t need to warm down
Step 4: Analysis: Compare the HR average in the first half of the test to the second half. When you hold an aerobic pace at the AeT, your HR will remain nearly constant for as long as an hour. If the HR drift is less than 5 percent, your starting HR was below AeT. If your HR rises more than 5 percent at that steady pace, your starting HR is higher than AeT. Repeat the test if necessary to get a correct measure.

AnT Test

Equipment needed: HR monitor ( not wrist based), a GPS watch and a track with a consistent gradient
Step 1: Warm up at an easy pace for at least 20-30 minutes and include a few faster 1-2 minute efforts so that you are fully warmed up
Step 2: Choose either a 30 minute or 60 minute test. 30 minutes is suited for those who are starting out and 60 minutes is suited for higher aerobically trained athletes with good muscular endurance.
Step 3: Start the test: run for the duration of the test ( 30 or 60 minutes) at a consistent moderate to hard effort pace. You want to be going as fast as you can but sustainably for the whole test without blowing up and having to slow down.
Step 4: Easy active warm down jog or walk for at least 20-30 minutes
Step 5: Analysis: first compare your pace in the first half to the second half to assess the validity of the test and your effort. If you were much faster in the second half it means you probably didn't run fast enough in the first half and conversely if you had to slow down a lot then you probably started out too hard or needed to do a shorter test.
Step 6: If the pace was fairly even then we can say that you were running at your maximum sustainable pace and the average HR for the test equates with the metabolic point where you are accumulating lactate at a high rate but you are still able to clear it aka the AnT and top end of zone 3.