Heart Rate: Everything You Want To Know




As the title implies, this article is meant to be an in-depth guide to understanding Heart Rate (HR) and how it can be used—both properly and improperly—as a training tool.

We're going to cover the following topics in this article, feel free to use the table of contents to skip ahead.




Heart Rate: The number of times your heart beats in one minute, hence the abbreviation “BPM” or Beats Per Minute.
Resting Heart Rate:  Your Heart Rate while you are at complete rest, usually measured in the morning in bed right after waking up.
Max Heart Rate: The absolute highest heart rate you can attain.
Threshold Heart Rate: The heart rate associated with your threshold power or threshold pace, unlike Resting and Max Heart Rate, there is no definitive definition or value for Threshold Heart Rate. For reference, The Sufferfest app uses the term Lactate Threshold Heart Rate (LTHR).
Heart Rate Training Zones: Multiple ranges of heart rate values, usually based off of Max Heart Rate or Threshold Heart Rate.  These ranges are used to set training intensities. Like Threshold Heart Rate, there are no definitive values here, and training zones vary depending upon the testing protocol or software.


Vital Point 1: Whether we’re talking about Max Heart Rate or Threshold Heart Rate, your heart rate is unique to you. You should not compare it to someone else's, period.  You should never use someone else’s values to guide your training, nor should you use heart rate to determine how fit you are relative to someone else.

Vital Point 2: You cannot accurately use age-based calculations to set your heart rate training zones.

  • Yes, Max Heart Rate and Threshold Heart Rate will decline as you age.  However, All 18-year-olds do NOT have the same max heart rate, just as all 65-year-olds do NOT have the same max heart rate.
  • If you're healthy enough for high-intensity exercise, then you need to do a fitness test designed to find your correct training zones.
  • If you're not healthy enough for high-intensity exercise, there is a danger that using age-based calculations might give you targets that would pose a health risk if you follow them.
  • Regardless of your perceived health, you should always consult a doctor before undertaking a new exercise program, especially one with high intensity or one that uses HR zones to determine effort levels.


  • Blood.  Blood is responsible for transporting oxygen, nutrients, hormones, waste products, heat and other goodies around your body.  Without a beating heart, you have no transportation, and no transportation means you are not long for this world.
  • Pacemaker Cells. Pacemaker Cells, ensure that your heart ticks away at 100bpm without any other input from your body.


  • The volume of blood your heart moves per minute is referred to as Cardiac Output. Your heart can increase or decrease Cardiac Output in two ways:
    • Heart Rate: The number of beats per minute.
    • Stroke Volume: This is the force of each beat, which directly affects the volume of blood the heart pumps per beat.
  • Both Heart Rate and Stroke Volume are controlled mainly by your Autonomic Nervous System (ANS), and hormones.  
  • The ANS itself is made up of two different branches that control most of your body’s “unconscious” actions.
    • The Parasympathetic Nervous System (PNS): This controls your “rest and digest” functions
    • The Sympathetic Nervous System (SNS): This system is responsible for the “fight or flight” response.
  • Both the PNS and the SNS directly affect heart rate.   
    • Increased PNS activity will LOWER your heart rate, this is why your resting heart rate is not always 100bpm, the default speed of your pacemaker cells.
    • Increased SNS activity will RAISE your heart rate (more on this later).
  • The hormones that are primarily responsible for changes in your heart rate are epinephrine and norepinephrine, also known as adrenaline and noradrenaline respectively
    • During a "fight or flight" response your body releases epinephrine, which increases your heart rate.
    • Not only does epinephrine increase your heart rate, but it also causes the muscles in your heart to contract with more force. This is why you can feel your heart pounding in your chest when you have a good scare.
  • Heart Rate is a RESPONSE to what is going on in your body.  Your body is full of different sensors that detect changes throughout your whole cardiovascular system (heart and blood vessels). These sensors monitor changes like decreases in oxygen saturation, increases in Hydrogen Ions, the presence of different hormones, and changes in blood pressure, just to name a few.  
  • Your body is reacting to these sensors at all times, and will send commands to increase or decrease your heart rate based upon the changes it senses.


  • When you hop on your bike and your muscles start working, they use up more oxygen, give off more CO2, use up nutrients and churn out waste products (metabolites).
  • Those sensors all throughout your body sense these changes and tell your heart it isn’t delivering enough blood to your muscles, so it needs to get to work!
  • Initially, your PNS (which is responsible for “rest” functions) will stop sending signals to your heart, and your SNS will take over
  • To hit your Max Heart Rate you need the final kick that comes from hormones like epinephrine.  


  • Endurance exercise will increase the size of your heart over time by forcing it to pump more blood for extended periods of time.
    • This increased volume per beat will cause your resting heart rate to drop.
  • Endurance exercise increases total blood volume through increased plasma volume. Since blood is the vehicle that all of the hearts “transportation” demands require, more blood means the heart can increase the work it can do. The prevalence of “blood doping” as an (illegal) performance-enhancing technique for cyclists and the controversy around the practice shows how important total blood volume is for endurance sports.   


  • It’s important to understand that heart rate is reactive. It’s a RESPONSE to a change in intensity. Do not expect your heart rate to instantly climb to Z5 or drop to Z1 as soon as an interval starts or ends. Heart rate is a reaction to what you just did, not what you’re doing right now.
  • A power meter tells you what you’re doing right now.; HR can only tell you what your body was doing several seconds ago. The reactive nature of heart rate is why you can't use HR Zones in the same manner you use Power Zones.
  • When using a heart rate monitor in training, you can (and should) still use Relative Perceived Exertion (RPE), to fine-tune your efforts.  Even if you feel you are an expert with RPE, you should still brush up on it by reading this article.
  • Because of this, heart rate should not be used to dictate effort in these situations:
    • Short-duration intervals (anything under 4 minutes)
    • High-Intensity Intervals (Anytime you're more than 10% above your Functional Threshold Power, or FTP))
    • An effort with constant surges.
  • Heart rate is an excellent gauge in these situations:
    • Fine-tuning long, steady-state efforts where the goal is to remain under FTP the entire time (sweet-spot and tempo efforts).
    • Ensuring that you aren’t going too hard during Endurance/Base/Zone 2 rides. The benefits of these rides require that specific Zone 2 intensity.
    • Recovery Days. Seriously, these days are good for you, but they are only good for you if it is a genuine recovery spin, meaning your HR never climbs above Zone 1.


Cardiac Drift is a phenomenon where heart rate increases during an effort, even though the workload (power) remains constant. In essence, your heart is having to beat faster to keep up with the same workload. Cardiac Drift has two flavors:

1) During sustained efforts above FTP

  • When working above FTP, your body will be making waste products (metabolites) faster than your body can clear them.
    • Your body senses the continuous increase in waste products and continues to send signals to your heart telling it to increase cardiac output.
    • Your body will keep doing this until you either hit your Max Heart Rate or until you're no longer able to hold the effort (or both).
  • This type of Cardiac Drift can be a useful tool for fine-tuning long intervals right at FTP. If your HR creeps above your LTHR within the first 5 minutes and then continues to climb during your first interval, chances are you're riding above your FTP (for more information on LTHR see section 9 below). Always remember that your FTP will vary from one day to another, and will rarely be EXACTLY the value you determined from your most recent  power test.

2) During long steady efforts at or below FTP.

The second scenario does not follow the same logic as above. At these longer steady worloads your body should have no problem keeping up the demanded cardiac output. Why would your heart rate continue to climb during these long efforts?

  • The two culprits here are dehydration and overheating.
  • An increase in core body temperature causes heavy sweating. The primary source of the water in sweat is the plasma in your blood. As you sweat and become dehydrated, your blood volume will begin to drop.
    • Remember, a given effort requires a specific cardiac output, which depends not just on heart rate, but on the volume of blood pumped per beat.
    • Once blood volume begins to drop, your heart pumps out less blood per beat. To compensate, your heart rate has to increase.
    • Compounding the issue, as core temperature rises, your body will divert more blood to your skin in an attempt to get rid of that extra heat. Your heart is forced to increase cardiac output to supply the higher demands of both your legs and your skin.
  • Generally, Cardiac Drift can be reduced if you are adequately cool and stay properly hydrated. (for tips on how to stay cool check out this article). This type of Cardiac Drift isn't necessarily a "bad" thing, especially during your longest training rides.


  • Impacts of fatigue on the Parasympathetic Nervous System (PNS)
    • A low resting heart rate is generally a sign of good aerobic fitness, thanks to increased stroke volume and increased blood volume.
    • When you're at rest, the PNS is continuously sending signals to your heart to keep heart rate low. Remember: decreased PNS activity raises heart rate, while increased PNS activity lowers heart rate. Fatigue can impact your resting heart rate by either increasing it or lowering PNS activity (if only it was as simple as one of the other!!)
  • Impacts of fatigue on the Sympathetic Nervous System (SNS)
    • Decreased Max Heart Rate
    • Your heart rate will be slow to increase with increased effort
    • Your heart rate will be slow to drop with a reduced effort
    • Consecutive days and weeks of hard training will put plenty of stress on your SNS. This constant stress will impair how well your SNS is functioning. This causes:
  • Other signs of fatigue not explicitly linked to heart rate are:
    • Trouble getting to sleep or staying asleep, despite being extremely tired during the day.
    • Excessive hunger
    • Constantly feeling too hot without running a fever
    • Mood swings
    • Sudden increase or decrease in weight


  • To accurately determine LTHR you can't have any fatigue in your system, meaning you must test when fresh to get the most accurate LTHR.
  • Once you have been training for a couple of years, your LTHR will not change significantly during a season (unless you spend a substantial amount of time off the bike)
    • If you're training consistently and find that your LTHR is much lower from some tests compared to others, chances are you're carrying fatigue, and should not be testing anyway.
  • Every testing protocol for determining LTHR has specific training zones associated with it.  Make sure you use the training zones that go with the testing protocol you used.
    • If you do not use the Full Frontal fitness test in The Sufferfest app to set your LTHR, the heart rate targets for workouts in the app might not be correct.
  • LTHR does not dictate your Max Heart Rate.  How long and individual can sustain a heart rate above LTHR varies significantly.
    • This variability is why heart rate is not a good metric to use when pacing high intensity efforts.   
    • The only time you should see a target heart rate that exceeds your LTHR is during near maximal efforts. During such efforts you should be using RPE and (ideally) power to guide your effort, not heart rate.
    • Hormones like adrenaline will increase heart rate. Never use heart rate values from a race/event to set your zones. Your LTHR and zones will be artificially high.
  • Dehydration and temperature play a big role in heart rate. If you test while dehydrated or without proper cooling, your LTHR and resulting training zones will be artificially high.
    • Conversely, if you test in an excessively cool environment, but train in a hotter one, your LTHR and training zones will be artificially low.


While there are many ways to set LTHR, we at APEX take your average heart rate from the 20-minute effort in Full Frontal as we feel it is the most accurate.Why?

  • When you complete a single 30-minute or 20-minute test, you're riding above FTP. With these tests, you take a set percentage of your average power to accommodate this. However, similar subtractions are usually not made for LTHR (though the zones themselves can accommodate some of this)
  • We know that a given effort level (power output) requires a specific cardiac output. That means power above FTP requires a higher cardiac output than power at FTP.
    • Your average power for the 20-minute or 30-minute interval of a single effort test will always be above FTP.
    • That means your average heart rate for these tests will be more than the heart rate your body would need to hold FTP
  • Unlike conventional FTP tests, the 20-minute effort in Full Frontal comes directly after a 5-minute maximal effort and 6-minute recovery. Because of this sequence of efforts, we know that you will be limited to riding right at your FTP for the full 20-minutes (which is why we take 100% of the average power from this 20-minute effort to set FTP). Since your effort level is limited to your FTP, so will your cardiac output.
  • Most importantly, when using your LTHR from Full Frontal, you should use the corresponding zones 


Long before power meters became the training tool of choice, athletes who wanted to get deeper insight into their performance and train more effectively used a sophisticated, finely-tuned instrument available free to anyone with a pulse: heart rate. And though power meters do provide accurate, objective data, heart rate remains a powerful training tool, as long as you know how to use it effectively. That means keeping these key points in mind:

  1. Your heart rate, like your fingerprint, is unique to you. To use it properly as a training tool you need to do individual testing.
  2. Heart rate is reactive. It’s a response to what you’ve done, not what you’re doing. There will always be a delay between changes in effort and changes in heart rate.
  3. Heart rate is most effective during longer, steady efforts. For short, high-intensity efforts, use RPE and a power meter if you have one.
  4. Heart rate training zones are unique to the test used to establish them. You can’t take the zones from one test and use them with an app or training tool that uses a different test.
  5. Heart rate can vary according to many factors, including sleep, hydration, temperature, caffeine intake, and stress. Recognizing why your heart rate is higher or lower than normal will help you decide if you can press on, or if you should back off and rest up.
  6. Listen to your heart. You might be surprised at how much it can tell you.
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