In a previous article, we’ve discussed Training using heart rate zones, which gives some of the theoretical details about defining and using heart rate zones in your training. In this article, we take a look at how monitoring heart rate and the use of heart rate zones has supported a particular type of exercise session: 1 hour of cycling effort purely in the aerobic zones (Zones 1, 2 and 3). This type of training is particularly important for building endurance and preventing fatigue caused by exercising above your anaerobic threshold. When cycling, such a session can often be useful during the winter when getting out on the bike may be happening less frequently, and group rides are slower than they might be during the summer racing season.

To understand the session, let’s take a look at graph of heart rate against time for the 90 minutes or so this session took using the screenshot below. Initially the heart rate started around 100bpm, then during 20-25 minutes of warm up rose to around 155. By monitoring heart rate during their session, our cyclist was able to control their effort to ensure that the heart rate didn’t go above the anaerobic threshold (AT) boundary between Zone 3 and Zone 4 for any significant period of time during the main hour-long effort of the workout. After completing the work, a 5 minute cool-down easily brings the heart rate back to normal levels.

This effort is then summarised in the bar graphs at the top of the screen, which show that just over 60 minutes is spent in Zone 3 (yellow), and that the only other significant time in the workout is spent in Zone 1 and Zone 2 (from the warm-up and cool-down periods). That pattern is the hall-mark of this kind of session – any significant time in Zone 4 or Zone 5 would be a sign that too much effort was being expended, and would like also show as a prolonged period required to bring heart rate back to normal levels at the end of the workout.

It’s interesting to note the two sharp spikes at around 19 and 22 minutes, which were recorded during the warm-up period. Our cyclist did these short bursts of near-max intensity to allow themselves to more easily get their heart rate up to the desired level for the actual work of the session. While this may not be true for everyone, our cyclist here finds that without a short burst of effort during the warm-up it can be difficult to comfortably maintain their heart rate near the anaerobic threshold, or indeed to even get it there in the first place!

Zooming in to the hour-long period of work gives even more detail to understand what happened during this session: as you would expect, it is hard to keep heart rate constant while training (even on a turbo-trainer!), and so it varies throughout the workout. However, our cyclist has carefully ensured that whenever it gets near the anaerobic threshold boundary they’ve eased off, and if it drops too low then a little more effort is put in.

Acknowledgements

All images shown in this article are screenshots taken showing actual data recorded by Heart Graph for iOS and Apple Watch. Find out more about the features of Heart Graph by viewing our Tutorial Videos.

About the author

Dr Thomas Wright, Director of Smoky Cat Software Ltd., studied at the University of Oxford, and has spent 1000s of hours rowing and coaching rowing, and road-cycle racing. As well as being Men’s captain of St Catherine’s College Boat Club in 1997/98, he also participated in the University Lightweights Summer Squad in 1998, competing in an eight at the Henley Royal Regatta. As a member of the Oxford City Road Club, he was awarded the Frank Wraight Memorial Trophy in 2003 as the club’s cycling road race champion.

When starting out with a training program, one of the questions people ask is whether they are getting the most from the efforts they’re putting in. A common problem is actually pushing too hard for too long, which unless carefully managed can lead to over-training, a situation that not only takes its toll on the body, but also means that your performance can actually decrease as you continue training in the same way.

A carefully designed training program for aerobic activities such as running, cycling or rowing will involve a mix of training activities, including shorter, high-intensity sessions such as intervals, long “steady state” sessions for building base fitness and the all-important active recovery sessions. These recovery sessions are essential to give your body the time it needs to adapt to the training you’ve been doing, and help ensure that you are rested enough to push yourself to the appropriate level in the other sessions within your program.  It can often be better to do a well-managed active recovery session than to take a day completely off.

One essential ingredient to making sure that you’re actually implementing the training plan you’re working with is heart rate monitoring. Heart rate can give you a good idea of how hard your body is actually working, although it is relative to your personal physiology and absolute numbers will depend on the type of activity you’re doing. Because heart rate will vary throughout your training session, to make sense of it we need a way of extracting some simpler representative values: that’s where heart rate zones come in.

The easiest way of defining heart rate zones is based on maximum heart rate, which can be crudely estimated as ( 220 – your age ), e.g., a 20 year old may have a max heart rate of 200bpm (beats per minute), while a 50 year old may have a max heart rate of 170bpm. Alternatively you can use other techniques to measure it more accurately, for example as described in this RunnersWorld article. Five heart rate zones could be defined as:

• Zone 5: max * 0.9 and above (MAX)
• Zone 4: max * 0.8 up to max * 0.9 (Anaerobic)
• Zone 3: max * 0.7 up to max * 0.8 (Aerobic, Hard)
• Zone 2: max * 0.6 up to max * 0.7 (Aerobic, Moderate)
• Zone 1: max * 0.5 up to max * 0.6 (Aerobic, Easy)
• max * 0.5 and below: ignored as not significant

So for a 20 year old, the zones would be:

• Zone 5: 180bpm +
• Zone 4: 160…180bpm
• Zone 3: 140..160bpm
• Zone 2: 120..140bpm
• Zone 1: 100..120bpm
• Below 100bpm: ignored

The boundary between Zone 3 and Zone 4 is particularly important as it defines the point at which your body switches from efficient, lower power aerobic activity to less efficient, but higher power anaerobic activity. While you can train aerobically for very long periods, if you train with your heart rate above your anaerobic threshold you will be limited to perhaps 30-60 minutes before exhaustion. Using our above definition of heart rate zones puts the anaerobic threshold at 80% of maximum heart rate, although it is possible to more accurately measure this value as described in this Sports Fitness Advisor article.

Having defined the zones and recorded your heart rate throughout your session, you can then calculate the total amount of time spent in each of the different zones. It doesn’t matter whether you spend 10 minutes in a zone in one go, or as 10 individual sections of 1 minute each; only the total matters. The important thing is that by looking in the total time spent in each of the zones, and also the proportion of the session spent in each zone, you can get an idea of how hard a session was.

As an example, the Apple Watch screenshot below shows a snapshot of the time spent in each heart rate zone during the first part of a fairly hard session: already in under 15 minutes over 3 minutes has been spent above the anaerobic threshold (AT), although the most time is spent in the moderate, aerobic Zone 2. Using this information during your workout can allow you to decide if you’re sticking to your plan, working too hard, or taking it too easy; appropriate adjustments can then be made.

Different kinds of session should produce a zone breakdown with a different pattern: a steady state session would typically be spent in Zone 2 and Zone 3, and although an interval session should include time in Zone 5, there also needs to be time spent in the lower zones to allow for recovery in-between the intense bursts.  When doing an active recovery session, you should only have heart rate in Zone 1; anything more is too much and risks leading to over-training. Learning the patterns that are appropriate for you and your training regime can allow you to better understand your body and to optimise your sessions to maximise the benefits.

In future articles we will discuss how heart rate zones can apply to different kinds of workout sessions.

Acknowledgements

All images shown in this article are screenshots taken showing actual data recorded by Heart Graph for iOS and Apple Watch. Find out more about the features of Heart Graph by viewing our Tutorial Videos.

About the author

Dr Thomas Wright, Director of Smoky Cat Software Ltd., studied at the University of Oxford, and has spent 1000s of hours rowing and coaching rowing, and road-cycle racing. As well as being Men’s captain of St Catherine’s College Boat Club in 1997/98, he also participated in the University Lightweights Summer Squad in 1998, competing in an eight at the Henley Royal Regatta. As a member of the Oxford City Road Club, he was awarded the Frank Wraight Memorial Trophy in 2003 as the club’s cycling road race champion.