Trainright Guide to Heart Rate Training for Cycling

By Jim Rutberg,
CTS Pro Coach,
co-author “The Time-Crunched Cyclist”
and “Training Essentials for Ultrarunning”

Although cycling power meters are widely available, heart rate is still valuable and useful as a training tool. If you don’t have a power meter, you can use heart rate training zones to target specific aspects of fitness and performance. And if you do train with power, heart rate provides important context to your workouts. Whether you are a beginner or an experienced cyclist, here’s what you need to know about training with heart rate.

How heart rate can be used in cycling training

Many athletes are familiar with using a heart rate monitor during exercise. You can either use a heart rate strap paired to a cycling computer or watch, or you can use a wrist-mounted monitor like an Apple Watch, Fitbit, or Garmin. Be aware, however, that the wrist-mounted options may not be as accurate as chest-worn monitors. That said, heart rate has multiple uses for athletes:

• Heart rate as an intensity gauge during exercise
  This is the most common use case and the one that will be discussed in greater detail below.
• Heart rate variability
  The interval between heartbeats is not constant, and variability in this rhythm can be indicative of the sensitivity level of your parasympathetic nervous system. Heart rate variability is described in depth in this article. Briefly, higher HRV indicates greater responsiveness to acute stimuli, which means you’re likely more rested. Lower HRV may suggest heightened fatigue. (Resources: here and here)
• Resting heart rate
  Resting heart rate is typically measured immediately after waking but before you get out of bed. From day to day, resting heart rate should stay relatively constant. Over time, an endurance athlete’s resting heart rate may decrease, but a low resting heart rate shouldn’t necessarily be a training goal. Elevated resting heart rate may be an indication of fatigue and is often observed in athletes struggling with overtraining. However, it can also result from dehydration or altitude exposure.

Training with heart rate vs. power

Cyclists are fortunate because power meters provide a method to directly measure work performed on the bike. That leads some athletes and coaches to mistakenly dismiss heart rate as irrelevant or passé. It is more accurate to say heart rate is not as reliable as power for gauging training intensity and workload. Can you train effectively without a power meter? Absolutely. Heart rate training works and has worked since heart rate monitors became widely available 40 years ago.

For many cyclists, training with power and heart rate are not all-or-nothing propositions. It is common for cyclists to have a power meter on one of a handful of bikes, plus maybe a smart trainer that has an ergometer function. As you incorporate multiple bikes into your training, heart rate is a convenient and lower-cost way to consistently gather data.

Factors that affect exercise heart rate

The following section was adapted from “Training Essentials for Ultrarunning”, a book I co-authored with CTS Coach Jason Koop. It should be noted that Rating of Perceived Exertion (described later) is the preferred intensity gauge for trail runners.

The heart rate value on a cycling head unit is an observation of your body’s response to exercise. It’s not a direct measure of the work being done. Instead, the work is being done primarily by muscles, which in turn demand more oxygen from the cardiovascular system.

Because oxygen is delivered via red blood cells, heart rate increases as demand for oxygen rises. It’s an indirect observation of what’s happening at the muscular level. Research has shown conclusively that there’s a strong correlation between heart rate response and changes in an athlete’s workload, and that research allowed sports scientists and coaches to start creating heart rate training zones back in the 1980s.

As sports science evolved over the decades we learned that many factors affect an athlete’s heart rate. Those factors reveal significant disadvantages to using heart rate response as a training tool. The following factors are known to influence exercise heart rate:

Core Temperature

As your core temperature increases, heart rate at a given exercise intensity will increase. Your circulatory system carries heat from your core to your extremities to aid with conductive and radiant cooling.

Caffeine and Other Stimulants

When you consume caffeine, either from your morning cup of coffee or from a caffeinated gel during a training session or race, your heart rate increases.

Excitation/Nervousness

A race is an exciting event, and that causes an adrenal response that increases your heart rate. Other emotional responses, including frustration, anger, and anxiety, can also affect heart rate.

Hydration Status

Although heart rate changes due to hydration status are often with or concurrent with impacts from core temperature, your heart rate can increase from dehydration with or without a rise in core temperature. As your blood volume diminishes, your heart needs to beat faster to deliver the same amount of oxygen per minute.

Elevation

Most athletes train within a small range of elevations in their local area, but goal races may feature dramatically different elevation profiles. Your heart rate response to exercise will change as you reach and exceed about 5,000 feet above sea level. The effect of altitude on performance and heart rate response increases as you go higher. Heart rate and respiration rate increase at elevation. The reduced partial pressure of oxygen in the air you’re breathing means there are fewer oxygen molecules in each lungful of air. More details are available for preparing for events at altitude and the pros and cons of altitude training camps.

Fatigue

While many of the factors that impact heart rate act to increase it, fatigue often suppresses it. When you are fatigued, your heart rate response to increasing energy demand is slower and blunted. A tired athlete will see heart rate climb more slowly at the beginning of an interval or hard effort and will struggle to achieve the heart rate normally associated with a given intensity level.

The factors that affect exercise heart rate don’t negate its usefulness as a training tool. Rather, they mean you must consider them when you observe heart rate values that seem higher or lower than normal.

Heart rate training zones

The body doesn’t really have discreet energy systems that switch on and off. You are always making energy available to muscles and tissues aerobically and anaerobically. Your relative demand for energy shifts emphasis to the mechanisms best suited to meet your immediate needs.

When we create training zones (heart rate, power, or RPE), we are focusing workload on one area of this spectrum. The goal is to move the inflection points for these shifts. For instance, focusing time-at-intensity near lactate threshold can increase the amount of work you can perform aerobically before reaching lactate threshold.

Increases in heart rate correspond reliably with increases in exercise workload. As a result, we can use lactate threshold testing (lab test) or Functional Threshold Heart Rate testing (field test) to calculate heart rate training zones.

Functional Threshold Heart Rate testing

A single 20-minute time trial or two 8-minute time trials are common field tests used to establish heart rate training zones. The tests for heart rate are identical to those described here for Functional Threshold Power. The calculations based on your heart rate test results are different, however, and described below.

Which test is right for you? Generally, the 8-minute test is better for novice athletes who may not have the experience to effectively pace a 20-minute time trial. Very fit athletes may do better with the 20-minute test. This is because their anaerobic capacity may skew their result for the shorter test.

Calculating heart rate training zones

After you complete a field test, you’ll use your average heart rate from a single 20-minute time trial, or the higher of the two average heart rates from the 8-minute efforts, to calculate training ranges.

Step 1: Multiply by conversion factor

As the duration of an effort increases, the percentage of energy supplied anaerobically decreases and the percentage of energy supplied aerobically increases. To account for this, we apply a conversion factor to field test average heart rates (and power values). If you complete a single 20-minute test, multiply your average heart rate by .95. If you complete two 8-minute time trials, multiply the higher of the two average heart rates by .93.

Step 2: Create heart rate training zones

There are multiple protocols for establishing training zones. Some have five zones, others have up to nine. If you use software like TrainingPeaks or Strava, or have head units from Garmin, Lezyne, or SRM, you can choose your preferred protocol and the calculations will be automated. At CTS we use a 5-zone protocol and then make narrower zone recommendations for specific CTS Workouts. The tables below show the percentages for the low and high limits of CTS Zones, and then individual heart rate prescriptions for CTS Workouts. Use the value calculated in Step 1 to derive your personal low and high limits.

Resources: CTS Cycling Field Test Instructions and Training Zone Calculator

What is Aerobic Decoupling?

Aerobic decoupling (previously known as cardiac drift) is a phenomenon that may affect exercise heart rate during individual rides. We’ve already explained how heart rate response can be affected by internal and external factors. Hydration status, core temperature, and ambient temperature can all change from the beginning to end of a single ride or set of intervals. As a result, it is common for heart rate to gradually increase during interval workouts – even when power output remains constant.

Aerobic decoupling can also occur during long rides or races without changes in hydration status, core temperature, or ambient temperature. This reflects the increased internal cost to produce the external workload in, say, the third hour of a ride compared to the first. Dr. Stephen Seiler discusses this aspect of an athlete’s durability in this podcast with Coach Adam Pulford.

TrainingPeaks incorporates a measure for aerobic decoupling by comparing power to heart rate (Pwr:HR) for a given time. For long intervals and entire rides, coaches often consider decoupling of up to 5% as an indication of good aerobic development. During short and hard efforts, Pwr:HR is likely to be high (i.e. 12-15%). And during long group rides or races where riders spend long periods in the draft, Pwr:HR may be negative. Resource: All About Aerobic Endurance and Decoupling, by Joe Friel.

Heart rate and Rating of Perceived Exertion (RPE)

Rating of perceived exertion is a simple and accurate way to gauge exercise intensity. It is especially useful for providing context to power and heart rate data.

For instance, over time you may learn that on “a good day”, an RPE of 4-5 (conversational, aerobic pace) correlates to a heart rate of 130-140 beats per minute. If you have a power meter, too, this may also correlate to 160-175 watts. As a result, a day when an RPE of 4-5 results in a heart rate of 150-155 can be a red flag. Something is not normal with your heart rate response.

The same can be said for a day when heart rate is lower than normal during a harder effort, like an RPE 7-8 (lactate threshold intensity). Perhaps you normally complete lactate threshold or FTP workouts at 160-165 BPM and 250 watts. Today the RPE and power are normal but your heart rate won’t rise about 150 BPM. Or, pushing hard enough for your heart rate to reach 160 bpm feels like an all-out 10/10 RPE effort.

What should you do about these discrepancies? Prioritize RPE and power output over heart rate during individual workouts. Watch for heart rate trends over a 3-5 day period before considering changes to your future training or recovery plans.

As discussed more fully here (Resource: RPE: How to use Rating of Perceived Exertion in Training and Racing), CTS Coaches help athletes use training data to learn how to pace efforts in training and racing by RPE.

Frequently asked questions about heart rate training for cycling

Athletes have been training with heart rate for decades, and there are some consistent questions and misconceptions out there.

• Does maximum heart rate matter?
  From an exercise standpoint, not really. Cardiac output (stroke volume x heart rate) matters because that determines how much blood you can circulate. Ideally, a high stroke volume and high maximum heart rate maximizes cardiac output. But a lower maximum heart rate with higher stroke volume works, too.
• Does maximum heart rate change with age?
  Although there is a lot of variability between people, your individual maximum heart rate is highest as a child and gradually decreases as you age. But again, stroke volume and muscle mass change over the course of a lifetime, too.
• Why isn’t my maximum heart rate ‘220 minus my age’?
  The equation: ‘HRmax = 220 – age in years’ is perhaps the most well-known heart rate formula by the general public. You can read more about its origin and validity here. It may be simple and convenient, but it is not accurate, especially for athletes. Endurance training alters the structure and function of your heart, lungs, blood vessels, and nervous system. As a result, your maximum heart rate is affected by more than your chronological age. Please stop using ‘220 minus age’ for… anything.

References:

Hajj-Boutros, Guy et al. “Wrist-worn devices for the measurement of heart rate and energy expenditure: A validation study for the Apple Watch 6, Polar Vantage V and Fitbit Sense.” European journal of sport science, 1-13. 31 Jan. 2022, doi:10.1080/17461391.2021.2023656

Robergs, Robert & Landwehr, Roberto. (2002). The surprising history of the “HRmax=220-age” equation. International Journal of Online Engineering – iJOE. 5.