Bytager the publication "The Limits of Heart Rate Measurement"
Heart rate in cycling training: limits and best practices
Heart rate (HR) is a commonly used indicator to assess exercise intensity during cycling training. However, many factors influence HR, which can lead to misinterpretation and limit its accuracy. We discuss HR drift and inertia phenomena, as well as external parameters that affect it. We offer solutions to optimize its use.
By Guillaume Judas – Photos: depositphotos.com
About forty years ago, heart rate monitoring devices during exercise revolutionized training in sports, particularly cycling. It took the emergence and widespread adoption of power meter devices a few years later to further refine and personalize the training of runners and cyclosportives. Even today, many practitioners are satisfied with heart rate measurement, which is widely available and widespread on most meters/GPS on the market..
Heart rate monitoring during exercise allows you to optimize the time spent in certain intensity zones, for faster and more targeted progress. Heart rate monitoring is also very useful for managing energy intake, limiting excesses linked to dehydration, anticipating illness or a health problem. the heart, or follow doctors' instructions based on age or medical history.
However, heart rate measurement has certain limitations.. And that in some cases, simply reading the HR is not relevant to indicate the intensity of the effort.
External factors influencing FC
Several external and physiological parameters can modify the HR for the same intensity of effort:
- High temperatures : significant heat complicates thermoregulation, forcing the heart to beat faster to maintain blood circulation, which increases HR.
- dehydration : fluid loss reduces blood volume, forcing the heart to speed up to ensure a stable cardiac output.
- Altitude : at high altitude, the lower availability of oxygen forces the body to increase HR to meet energy needs.
- Tired : a state of general fatigue, whether physical or mental, disrupts the adaptation of HR to effort, making the data less predictable.
FC inertia: a delay in adaptation
HR inertia is the time it takes for HR to adapt to a sudden increase in effort. This delay is particularly problematic during rapid changes in intensity.
Example: During an interval where the power increases from 150 W to 350 W, the HR does not instantly increase from 130 bpm to 195 bpm. It increases gradually, which can distort the evaluation of the effort.
Consequences : Over short, high-intensity intervals (e.g., 30 seconds at maximum aerobic power, or MAP), HR does not have time to reach its peak. Therefore, even if the cyclist reaches their VO2 max (maximal oxygen consumption), HR remains an unreliable indicator. Over long intervals (e.g., 8 minutes at threshold), trying to quickly reach a target HR can lead to starting too hard, with the risk of not maintaining the effort.
Cardiac drift: a progressive increase in heart rate during exercise
Cardiac drift refers to the gradual increase in heart rate during exercise, even when the intensity, measured by power (in watts), remains constant. This phenomenon is particularly noticeable during prolonged or repetitive sessions, such as intervals.
Example: During an interval session, you can produce 290 W for a heart rate of 180 bpm at the start of the session. At the end of the session, for the same heart rate of 180 bpm, the power can drop to 275 W due to fatigue. This shows that, as fatigue sets in, the same heart rate corresponds to a lower intensity.
Consequences : Relying solely on HR to determine the intensity zone can be misleading, as it does not accurately reflect the actual power output.
How to use FC effectively?
Given these limitations, here are some recommendations for optimally integrating HR into cycling training:
- High intensity : prescribing training based solely on HR is imprecise. For greater reliability, it is recommended to couple HR with the perceived exertion (RPE), which allows for subjective assessment of intensity, and/or to use a power meter, which directly measures the power output and remains the most reliable tool for managing intensity.
- At low intensity : HR is a good indicator in endurance zones, where cardiac drift is less marked. It helps ensure that the effort remains in the target zone.
- Physiological analysis : HR remains a valuable tool for analyzing physiological responses to training, such as the body's adaptation to effort or recovery. It helps understand how the cyclist reacts to different workloads.
Essential, but not always sufficient
Although heart rate is a useful and, from our point of view, essential indicator for monitoring one's health, it should not be used alone, especially at high intensity, due to drift, inertia and the many external factors that influence it.
For precise training, combining HR with a power sensor and perceived effort is the best approach. At low intensity or for longer efforts, HR remains a reliable and accessible tool, while its global analysis allows for a better understanding of physiological adaptations. By integrating these principles, you can optimize your training and achieve your goals with greater precision.
Bytager the publication "The Limits of Heart Rate Measurement"
