Medical Corner

Cardiovascular Drift – The Pulse Phenomenon Explained

Cardiovascular drift is a highly individual physiological reaction that depends on various factors. The heart rate increases with prolonged training time, even though the intensity of the training remains constant.

Heart Rate and Cardiovascular Drift

At the onset of exercise, the heart rate experiences an initial increase, stabilizing afterward while the activity intensity remains constant. This process usually completes within 1 or 2 minutes, depending on the athlete’s age. Cardiovascular drift can occur at any time when the workout intensity remains constant and is influenced by various variables such as the day’s resting heart rate, digestion, hydration, and other factors.

Reasons that can cause cardiovascular drift

  1. Increase in body temperature: Elevated body temperature, similar to the impact of running on a hot day, leads to an increase in heart rate.
  2. Sweating: Sweating leads to a significant loss of fluid that needs to be replenished, as dehydration has been shown to be a possible cause of cardiovascular drift (more info).
  3. High outdoor temperatures: Warm outdoor temperatures can lead to starting the workout with a higher heart rate.
  4. Previous workouts: Past training sessions can influence the level of fatigue and, consequently, heart rate.
  5. Multiple other factors that, when combined in the right way, can contribute to the manifestation of cardiovascular drift.

Effects of cardiovascular drift

  • “Competition for blood supply”: As the body tries to regulate body temperature, blood flow to the skin automatically increases. However, the active muscles also need to be supplied with blood, which leads to a “competition for blood supply”.
  • In order to maintain a constant oxygen intake, the heart has to pump more blood per minute to supply both the muscles and the “cooling system” with blood. In fact, nothing else changes, as processes such as breathing rate remain unchanged; only the heart rate increases.
  • Misinterpretation of heart rate: It is crucial to always remember that heart rate data must be interpreted and analyzed considering the specific situation and accounting for all factors.

Do not confuse heart rate delay with cardiovascular drift

Cardiovascular drift represents a variation in heart rate, even when the workout intensity remains constant. This phenomenon differs from the delayed adaptation of heart rate in response to changes in power output.

The delay manifests during interval workouts, where an initial increase in intensity results in an increase in heart rate only after a certain delay. Similarly, heart rate may decrease only after some time has passed since the end of an interval effort. However, it is important to emphasize that this delay does not correspond to the previously described cardiovascular drift.

The delay is caused by the fact that heart rate is a response to variations in effort and not a direct measurement of it. This makes heart rate susceptible to various factors such as meal timing and type, weather conditions, and stress levels. Using power values (watts) to measure training, on the other hand, provides a more accurate measurement since these values are not dependent on other variable factors.

Cardiovascular drift: Example of a runner

The example mentioned above is based on a runner’s speed and not watts, but since the training was conducted on flat terrain, this is irrelevant. The blue line indicates speed, while the red line represents heart rate. The first ten minutes of the run serve as a warm-up, with an increase in both speed and heart rate.

At the start of the first effort interval, an immediate increase in speed is observed, followed by a “slow” increase in heart rate (the same occurs when the interval effort is completed).

What is relevant is the following: while the runner’s speed remains approximately constant at each interval, heart rate initially increases, reaches a plateau, and increases again after about 10 minutes. Thus, heart rate increases while the workout intensity does not change. This phenomenon clearly highlights cardiovascular drift in a “real” training context.

Why is it important to understand cardiovascular drift?

Various misconceptions about heart rate, mainly due to cardiovascular drift, can lead to misleading conclusions or analyses.

  • Risk of undertraining: If, for example, you plan to run at a heart rate of 140-150 bpm, initially, you will be in this zone at the beginning of the workout. However, after some time, the heart rate will increase, and you might slow down the pace in an attempt to reduce it. This can lead to training at the wrong speed or intensity, as speed does not correspond to the level of effort or power output.
  • Impact on weight loss training: Many devices and online calculators still use heart rate to estimate calories burned. This approach falsely assumes that an increase in heart rate corresponds to a higher amount of calories burned. However, this is not valid when considering the presence of cardiovascular drift.

Are there options to manage cardiovascular drift?

Cardiovascular drift does not necessarily represent a negative aspect of training; it is simply a phenomenon to consider during physical activity analysis. Especially for those who base their workouts on heart rate, cardiovascular drift, and its side effects, can be misleading. Unfortunately, intervention possibilities are limited. If training indoors, a solution might be to “cool down” the body, for example, with a fan, to prevent a rapid increase in body temperature.

Additionally, maintaining an adequate level of hydration can help reduce cardiovascular drift. To optimize training, it might be useful to switch to power-based analysis.

In conclusion, it is important to understand that we can exert limited influence on cardiovascular drift. Therefore, the best approach is to acknowledge the phenomenon and try to minimize its impact by focusing on more objective parameters, such as speed on flat routes.


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