What is your heart rate?

Heart rate is simply the number of beats (contractions) per minute. The higher the heart rate, the higher the effort. The lower the heart rate, the lower the effort. 

Before reading this paper, there are a few other pieces of technical jargon you need to know. Firstly, we need to know MHR (max heart rate). This is the rate at which your heart pumps blood around your body when working at maximal cardiovascular effort and intensity. 

Next we need to know about RHR (resting heart rate). This is your heart rate while at rest when you are exposed to as little physiological and psychological stress as possible.   

Finally, we have HRR (heart rate reserve). Think of this as the range at which your heart can operate. This is the difference between your MHR and RHR. Later in this paper we will discuss how to test each of these as well as the validity of each test. 

Why train with heart rate?

1. Heart rate training is easily measured, tracked, compared and monitored. 
2. Get to know exactly how hard you’re working. 
3. Catch the earliest warning signs of burnout, illness and chronic fatigue. 

Pros and cons…

There are many advantages to training based off your heart rate.  It gives you a guide on what stimuli the training is providing. It helps you monitor your recovery and it can prevent you from blowing up during a longer workout or event. However it does have its limitations. It is important to remember there are many factors effecting your heart rate that will make heart rate training inaccurate. 

Sleep can greatly impact your heart’s response to training. If you’re running off little to no sleep your heart rate will be noticeably higher than it would typically be at a given effort level. This will alter your zones and skew your data. 

Nutrition and caffeine. What you consume has a direct impact on your heart rate. If you consume highly sugary foods or caffeine before or during your workout your heart rate will respond to this, even if your effort has not changed. 

Illness will wreak havoc on your system including your heart rate. Even the smallest cold can elevate your heart rate significantly. Although this one will also change your effort level reasonably linearly. 

Stress. Cortisol (the stress hormone) is very necrotic on your system. In relation to training, stress can simply change your perception of how hard your working. You could be working at a light intensity but feel as if you were running a 1,500m PB. Cortisol can also elevate your heart rate where you may be running at a much slower pace than typical but your heart rate is through the roof due to your fight and flight response or adrenal response. 

Weather and seasonal changes can also have a big impact on your heart rate, not just during a workout, but at rest as well. Depending on your heat acclimation, some people will find their RHR to be notably lower during colder seasons. You could have a RHR of 55 during the summer season because your body has to work harder to regulate your temperature, but in the winter you could find your RHR has now dropped to 47 or 48. This will have a direct effect on your training zone accuracy. 

Heart rate zones…

So we’ve likely all heard of heart rate training and zone training.  Perhaps you have a friend that bangs on about something called “zone two” training, but what does this actually mean and how is it used? 

Heart rate is broken into five zones, each designed to develop a differing aspect of cardiovascular fitness and performance. Each zone is individual to the athlete and based off a specific zone percentage of MHR. 

Before we break down what each zone is and what they do. It is very important to understand and appreciate the limitations and context of this training. Zone training is a guideline NOT a rule. While I will describe in detail the purpose of each, you must understand that while yes, there is a specific stimuli present in each zone, you will not stay exclusively in that zone at any given time. Each stimuli is present at each zone to some degree.  Although it is humans nature to want to create rudimentary, simplistic, black and white modules of how the world works, unfortunately this is not reality. There are many shades of grey and many ways to interpret data. With that said. Lets break down what each heart rate zone is.  

Zone 1

Zone 1 is a very light intensity between 50-60% of your MHR. Zone 1 is primarily used by athletes as a form of active recovery, either between intervals of a workout or for easy aerobic activity between workouts. Zone 1 training should feel very comfortable and non invasive.  Typically you should be able to carry out a conversation while exercising at this intensity as your body should not be struggling to either bring in oxygen or eliminate carbon dioxide. This is an intensity level that could be sustained for multiple hours consistently without taking any recovery.  Zone 1 is an intensity level where your body is able to process and utilize 100% of the lactic acid buildup present in the muscle belly without any anaerobic support. 

Zone 1 training can be used to enhance the recoverability of an athlete from an energetics and fueling point of view. These recovery sessions should always be kept under 40 minutes at the absolute maximum. Past 40 minutes you will be at maximal lactate clearance levels. From a recoverability point of view, there is no point continuing past this point. 

Two very important considerations an athlete and coach need to make to determine if zone 1 recovery runs are a worthy ingredient in the training diet are: a) Does the athlete possess the conditioning and resilience to tolerate the additional load on the body’s physiology i.e. tendons, ligaments, joints, bones etc. and b) Does the athlete’s skill acquisition allow them to retain proper joint angles, mechanics, postures and positions during the recovery task. If not, you may be introducing bad habits and increasing their likelihood of developing overuse and misuse injuries. This would defeat the purpose of enhancing recoverability. The fastest way to stop your improvement is to develop an injury. 

Zone 1 training is typically the intensity at which the heart is most optimally stretched and able to eject its full capacity of blood per beat. This is referred to as “Stroke Volume” (SV) – the amount of blood ejected per beat (measured in milliliters) beyond 60% MHR the SV remains the same. Only the heart rate itself increases.

Zone 2

Zone 2 is also light intensity but not as light as zone 1. This is between 60-70% MHR. This intensity can be sustained for a few hours. Many interesting and vital processes and stimuli occur in this zone. Firstly your body learns how to use fatty acids as a primary fuel substrate instead of relying on glucose. As an athlete becomes more elite their body can process fatty acids faster and they become available to  higher effort levels and intensity. This is vital to the success and longevity of endurance and ultra endurance athletes. 

Zone 2 is also where mitochondria biogenesis occurs.  This is where your body builds a bigger population of mitochondria, allowing you to process and clear metabolic fatigue and lactic acid faster. In endurance sports the mitochondria gobble up lactic acid and recycle it as a secondary fuel source. This also allows your body to better distribute fueling substrates throughout your body. 

Imagine you’re running down a hill for an extended period of time with the brakes on. Your quadriceps are going to be working pretty hard to do this and building a high level of fatigue and waste. All of a sudden you hit a climb. That transition from down hill to uphill can be pretty jarring. All of your fueling has been distributed to your quads for the downhill and now it is needed elsewhere, in the calf and glutes. Mitochondria allow you to process the built up lactic acid, recycle it back into energy before re distributing it to those glutes and calf muscles. The more mitochondria you have. The faster this process takes place, the less fatigued you feel, the faster you run. 

Zone 3

Zone 3 is a moderate effort level with your heart rate between 70-80% MHR. This training starts to feel moderately fatiguing, requiring a higher level of concentration to sustain intensity.  This will cause your respiration rate to increase in both depth and frequency as you will breath deeper and faster in this zone. It is very difficult to complete a sentence at this effort without breaking it up into small groupings of words. 

This zone has a large impact on your aerobic fitness and stresses your body’s ability to move and process oxygen and carbon dioxide. During zone 3 training lactic acid starts to accumulate in your bloodstream at a quicker rate. Your body is still able to process it and recycle it for energy. With this higher demand for lactate clearance. Mitochondrial biogenesis happens at this intensity as well, albeit with a slightly different outcome. At this intensity, instead of a primary development of mitochondria population the density of mitochondria is the primary adaption. Put simply, instead of replicating more mitochondria, you get bigger mitochondria. 

This zone is often referred to as ‘no mans land’ It is challenging enough that you could mistake this as very hard if you lacked the experience, discipline, or mental fortitude to know otherwise. It is challenging enough that your definitely out of your comfort zone but it’s not so challenging that you can’t sustain it for a decent length of time. Many amateur athletes make the mistake of spending all their time in this zone. It feels hard and you get fatigued. This training does not provide enough intensity to have a significant impact on your force application, power or speed but it is also not easy enough for you to recover completely. 

Zone 3 training uses more muscle fibers compared to zones 1 and 2. It also develops our capillary network allowing for more blood to get both in and out of our muscles in one go. This improves the economy of the working muscles, resulting in moderate levels of exercise feeling easier for longer. This develops the ability to glide and cruise at quicker paces for events like the half marathon and marathon. 

This is where a lot of athletes make an impactful error. Most athletes focus on zone 2 training before zone 3. This will develop a big population of “small” mitochondria. However if you grow your mitochondria first in density before quantity, in the long run this will develop a big population of “big” mitochondria. This is far more advantageous to all endurance sports as now your individual mitochondria can do more work and you have more of them. 

If you are in this boat of zone 2 before zone 3, don’t be discouraged as your mitochondria will return to your genetic set point after just 6 weeks without training them. It is therefore very easy to take a small R&R and recalibrate your training if you’re stuck in a plateau and don’t know what to do.  During this time you can still train, but just not Zone 2 or 3 based exercise.  For instance, you could do HIIT, strength, plyometrics, skill acquisition and technique development, as some examples. 

Zone 4

This training is between 80-90% MHR and is at a hard unsustainable intensity. Training at this intensity improves your speed endurance, stamina and lactate threshold as well as developing your efficiency at using glucose as a primary fueling substrate.  This training burns and is exhausting. Your muscles will ache and you will be unable to successful talk at this effort level. Only able to squeeze out a single word before needing to take a breath. 

Zone 4 training is the trickiest and the one with the highest risk to reward. Most overtraining occurs in this zone as it is very tricky to recover from. Inspired by professional athletes, many amateurs model after what they do with the idea that if you want to get better at something, copy the people that are better than you. What most don’t consider however is the years of conditioning and training that has gone into training how the professionals do. Not to mention the recoverability many professionals have. It is all well and good to hit double threshold runs if your able to rest, refuel and relax between the mornings and evening sessions, but if you need to work a physically demanding job for 10 hour between your mornings and evening sessions, you cannot expect to tolerate the same load as someone who does not have this work commitment. 

Spending too much time in zone 4 without allowing for the necessary recovery can also kill mitochondria, making all the zone 2 and 3 training redundant. 

Zone 4 is where lactate threshold is reached. This is the point at which the body produces more much H+ (hydrogen ions), lactic acid and metabolic waste products than it can clear and process. Leaving you in a surplus of lactic acid flooding your system. Typically lactate threshold is smack bang in the middle of zone 4 (85% MHR {4mmol/L of lactate}), as a generalisation. Lactate threshold has also been observed at slightly higher or slightly lower levels and efforts. e.g. 82% MHR or 88% MHR and 4.8mmol/L or 3.5mmol/L. This training will develop your body’s tolerance to lactic acid and this will result in lactic acid building slower and more controllably. 

Zone 4 training builds the population of mitochondria in fast twitch muscle fibers and develops power endurance allowing athletes to run at very fast paces for longer durations. All endurance athletes benefit from this training, however it is a crucial ingredient for athletes training middle distance track events from 800m up to 3,000m 5k and 10k athletes that will also benefit greatly from this training if prescribed appropriately. 

Zone 5

Zone 5 training is very hard, and is defined as between 90-100% MHR. This training induces the highest amount of blood lactate at the fastest rate. High zone 5 (95-100%) can only be sustained for around 40 seconds in even the highest trained athlete. Low zone 5 (90-95%) can be sustained for a little bit longer, but nothing substantial. Zone 5 is where your body is producing as much force as possible and your muscles and heart are contracting as hard as possible, as fast as possible. Lactic acid is produced at a rate that is impossible to recycle or use. While top end intensity can be sustained for up to 40 seconds, top end speed can only be sustained for a matter of meters before deceleration will begin. During zone 5, the athlete is breathless and unable to speak. 

Training in zone 5 can improve your top speed, however there are many neural and technique requirements to improving speed, so zone 5 training alone won’t cut it. Training at zone 5 will use as many muscle fibers as possible and develop the density of mitochondria in fast twitch muscle fibers. This improvement in mitochondria density will have a direct impact on improving endurance as is why endurance athletes incorporate short sprints into their training through the use of strides, pick ups, hill sprints or stair sprints. All runners should sprint! All runners should sprint year round! Zone 5 training is also utilised in sprint athletes to develop their starts and acceleration. 

Training in zone 5 is mostly measured by time instead of actually tracking heart rate. It is too difficult to check your heart rate while training at such an intensity. You can track your heart rate through the session and reflect on it after the session or during long recovery intervals. 

Heart rate zones summery

Zone 1 (warm up, cool down and recoverability)

• Very light intensity between 50-60% MHR
• Aids and enhances recovery 
• Improves heart health 
• Example workout: 30-40min easy run entirely at zone one. 

Zone 2 (aerobic support & base building)

• Light intensity between 60-70% MHR
• Develops resistance to fatigue signaling
• Improve base fitness
• Uses fatty acid as a fuel source
• Increases mitochondria population 
• Example workout: 60-80min tempo run, sustaining effort between 60-70% MHR
• Example workout: 60min alternating between 600m @70% HMR and 400m @60%MHR

Zone 3 (aerobic endurance & marathon prep)

• Moderate intensity between 70-80% MHR
• Develops resistance to fatigue signaling 
• Improve muscle recruitment 
• Increases mitochondria density 
• Develops long distance speed endurance (half marathon & marathon specific)
• Example workout: 4x 10min @70-80% MHR w/ 5min @ 50-60% MHR recovery 
• Example workout: 2 hour tempo @60-70% MHR w/ 5min surges @ 70-80% MHR
• IMPORTANT: successful zone 3 training must incorporate periods of running at zone 1 or 2.  

Zone 4 (anaerobic capacity & lactate threshold)

• High intensity between 80-90% MHR
• Improved lactate threshold and speed endurance (800m, 1,500m, 3k, 5k and 10k specific) 
• Increase mitochondrial population (fast twitch)
• Example workout: 10x 400m @ lactate threshold w/ 200m @ 60-70% MHR recovery 
• Example workout: 6x 2:00 @80-90% MHR w/ 1:00 @50-60% MHR 

Zone 5 (maximum effort, speed and power)

• Very high intensity between 90-100% MHR
• Improves speed and power
• Increases mitochondrial density (fast twitch) 
• Improves speed endurance (200, 400m specific)
• Increases force production 
• Increases muscular recruitment. 
• Example workout: 5 sets of 3x 30sec @ max effort w/ 1:00 rest 
• Example workout: 10x 40sec @90-95% MHR w/ 2:00 walk recovery 
• Example workout: 60min zone 1 run w/ 10-15sec bursts @90-100% MHR

Heart Rate Testing

So hopefully by now you are starting to understand that zone training is not an exact science, nor an exact rule, but more of a helpful guide to consider when analysing your training. It is not the be-all-and-end-all of endurance training. It’s just a piece of the puzzle. 

You have probably asked yourself by now. How do I accurately calculate all these things? How do I know my RHR? How do I know my MHR? How do I calculate my HRR, How do I calculate all of these training zones? Let’s look at that next. 

RHR

This is the easy one. All you need is a heart rate monitor to track your heart rate while you sleep. The more nights of data you can collect the better, although generally three nights will work fine. You may find over a two week period that your RHR bounces up and down by a few beats. Maybe you were 44 on Monday night, 43 on Tuesday night, 45 on Wednesday night and 42 on Thursday night. Simply take your average and that is your most common RHR. Do not include massive outlier during this period. If you had a restless night with a RHR of 59. Simply discard this as it is inaccurate. 

(RHR day 1 + RHR day 2 + RHR day 3) divided by 3 = Average RHR

MHR 

This is where things get tricky. Max heart rate has often been calculated with the old 220 – Age formula. This is incredibly inaccurate. If this were a true indicator it would suggest all people of the same age have the same max heart rate regardless of genetics, regardless of fitness, lifestyle, stress levels etc.  

So if 220 – Age is not the way to go, what do you do? There are a few options. The most accurate way to test MHR is with lab testing. This is the most controlled environment with the most sophisticated testing. There are a variety of tests you can do on a treadmill or a track. These could include progressive 60sec intervals. This would be starting at a moderate effort for 60sec, take a short break 30sec or so before repeating another 60sec interval at a higher effort. Repeat until failure. Analyze your heart rate once the session is complete. Another option would be the treadmill stress test. This would be a 10min hard effort on the treadmill. If you worked as hard as you can for around 10min this will put you to 80% or so of MHR. From there the final 60sec is as hard as possible. Your heart rate will not have much to go before reaching 100%. Once complete, analyze the final 60sec effort for the highest your heart rate spiked. This will likely be you MHR. 

MHR testing is where the difficult part of zone training comes in. If you do not know your MHR you cannot know your training zones. Most people will always hold back from their true max effort due to the associated discomfort and a lack of body awareness and skill to be able to achieve true max effort. Thus if you can not truly achieve max heart rate and therefore not truly identify your real heart rate zones. Is there much validity to using heart rate as your training guide?

If your MHR testing showed hour MHR to be 190. But you actually could have pressed a little harder and reached 195. This will skew all of your zones. You could be aiming for zone 2 cardio but actually be in zone 1. You could think you’re training lactate threshold through zone 4 but in reality your in zone 3. In the latter case, it is still hard enough and still going to make you work, so you would have a hard time knowing the difference. Thus your training would not be working as intended, your recovery periods between session types would be inaccurately prescribed and the stimulus and adaption you think your getting would be the wrong ones.   

HRR

The HRR formula is known as the Karvonen formula, 

MHR – RHR = HRR. 

Zone Calculations

Once we have workout out your HRR we can calculate your heart rate zones with it. simply use the formulas provided below:

• Z1 – minimum = HRR x 0.5 + RHR
• Z1 – maximum = HRR x 0.6 + RHR
• Z2 – minimum = HRR x 0.6 + RHR
• Z2 – maximum = HRR x 0.7 + RHR
• Z3 – minimum = HRR x 0.7 + RHR
• Z3 – maximum = HRR x 0.8 + RHR
• Z4 – minimum = HRR x 0.8 + RHR
• Z4 – maximum = HRR x 0.9 + RHR
• Z5 – minimum = HRR x 0.9 + RHR
• Z5 – maximum = HRR + RHR

MHR and SV

It is often thought that a higher MHR is a direct indicator of higher levels of cardiovascular fitness and that someone with a MHR of 200 is automatically fitter than an individual with a MHR of 180. While this can be the case, it is not always. The missing factor is stroke volume and contractility of the heart. 

If the heart can eject higher volumes of blood per beat and is stronger and larger. It may not need to beat as often to provide the body with the same quantity of blood. Let’s look at our example from earlier. If an individual had a MHR of 200 but could only pump 55ml of blood per beat. There cardiac output would be a total of 11,000ml of blood per minute while at zone 5 maximum effort training. If the person who topped out at 180 ejected 90ml of blood per beat. Then there cardiac output would be 16,200ml at zone 5. Now instead of comparing the simplistic 200 vs 180, we compare 11,000 and 16,200 and we see a clear and staggering difference. 

So when your thinking of fitness and heart rate and the correlation of each, we need to think about stroke volume and cardiac output and not just the heart rate itself.  There is a way of calculating your stroke volume and cardiac output. However similarly to our 220 – Age formula. It is very generalized and inaccurate.  

There is approximately 5L of blood circulating around your body. smaller people have slightly less blood volume and larger people slightly more. We can use that number and your RHR to roughly identify your cardiac output per beat. Then multiply that by your working heart rate to figure out how much blood is being circulated during exercise. 

small statured person (under 160cm)     4500 divided by RHR = SV 

medium statured person (160-180cm)    5000 divided by RHR = SV

large statured person (over 180cm)    5500 divided by RHR = SV

Once you have your SV figured out you can calculate your cardiac output (CO) at any given effort level in any heart rate zone.   

SV x HR = CO

Tracking RHR

Tracking your RHR can be a great way to identify when you’re coming down with illness or at the early stages of burn out as identified earlier in this article. Any stress in your life will effect your heart rate. If you track your RHR each night while you sleep and identify an outlier or a few outliers in a row, this is likely due to a compromised recoverability due to either too hard and too frequent training loads causing burn out. It could also be due to compromised immunity due to your body fighting off an infection. Either way, this is a good time to back off a bit and reassess your training loads to allow your body to cope better and thereby preventing both long lasting sickness and unwanted, easily avoided injury.