Cardiovascular drift is a well-known phenomenon, but the exact timing of its occurrence in the body remains unclear, as it is highly individual and depends on many different factors. Essentially, cardiovascular drift is when your heart rate increases even though your exercise intensity remains the same.
When you first start your training, your heart rate will go up and then start to plateau (= stay at about the same beats per minute) as long as the intensity remains. This happens after about 1 to 2 minutes (or later as it depends on the athlete’s age).
As long as the training intensity remains constant, cardiovascular drift can occur at any time (this depends on many different variables, such as your resting heart rate that day, your digestion, how much you have drunk, etc.).
Factors that can lead to Cardiac Drift
- Increase in core body temperature: the rise in body temperature does the same thing to your body as if you went running on a hot day. It increases your heart rate.
- Sweating (triggered by raising your body temperature, outside temperature, etc.): sweating causes you to lose a lot of body fluid, which needs to be reabsorbed, as it has been proven that dehydration can be responsible for triggering cardiovascular drift (read more).
- Warmer outside temperatures: this will lead you to start your workout with a higher heart rate.
- Your previous workouts: can have an effect on your level of fatigue and you might therefore have a higher heart rate than normal.
- There are many other factors that, in the right combination, can lead to Cardiac Drift.
Causes of the Cardiac Drift
- “Demand competition”: as the body wants to keep body temperature under control, this automatically increases blood flow to the skin. At the same time, the working muscles also need a large amount of blood flow. This can lead to “demand competition”.
- The body decreases the volume of blood that is pumped through your heart (= stroke volume). In order to keep the oxygen uptake and the amount of blood pumped by the heart equal for one minute, the heart rate increases. Nothing really changes for you, because processes such as your breathing rhythm remain the same, only the heart rate increases.
- Misinterpretation of the heart rate: always remember that your heart rate data must always be interpreted and analysed in relation to the given situation; ALL factors must be taken into account.
Don’t confuse the lag of your heart rate and the Cardiac Drift
Cardiac Drift is a change in heart rate even though your training intensity remains the same. However, it is not the same phenomenon as a delayed adaptation of heart rate to a change in power output. Delayed adaptation occurs, for example, during interval training. If the intensity is increased at the beginning of a workout, the heart rate will only increase after a delay. The same happens when the heart rate drops again after an interval effort. However, this delay is not the cardiovascular drift described above.
The delay is due to the fact that the heart rate is a reaction to a change in force/work input and not a measurement of it. This makes heart rate very dependent on various factors such as what and when you ate, weather, stress levels, etc. If you use wattage values to measure your training, then these values are not dependent on other factors and are not variable. Therefore, this is a more accurate way to document your training. We have covered this topic before, so if you are interested, click on the following links:
Cardiac Drift – Athlete Example
The example shown above (of a runner) is based on speed and not watts, but since the training took place on flat terrain, it doesn’t matter. The blue line marks the speed, while the red line represents the heart rate. The first ten minutes of the run are the warm-up – speed and heart rate increase.
At the start of the first interval effort, you can see how the speed immediately goes up while the heart rate “slowly” follows (the same happens when the interval effort is finished). This effect has already been discussed in the following article on the pros and cons of training with heart rate versus, for example, watts (read it again here).
What is relevant, however, is the following: While the interval speed remains approximately the same each time, the athlete’s heart rate increases initially, reaches a plateau and then increases again after about 10 minutes. The heart rate thus increases while the training intensity does not change. This phenomenon is exactly the cardiovascular drift, illustrated in a “real” workout.
Why is it so important to know about the Cardiac Drift ?
There are many misinterpretations of heart rate (including but not limited to) due to cardiovascular drift that can lead to incorrect conclusions/analysis.
1. Tendency to under-train: For example, if you are meant to run at 140-150 beats per minute, you will be in that zone at the beginning of your training but after time, your heart rate will go up and you will reduce your pace, trying to stay in the correct heart rate window. This slowing down of the training will cause you to train at the wrong speed/intensity. The speed does not match your fatigue level or power output.
2. Training to lose weight: Many machines and online calculators still use heart rate to calculate the number of calories burned. Accordingly, the machine assumes that you will burn more calories if you increase your heart rate. However, this is not the case with cardiovascular drift.
Is there anything that can be done about it?
Actually, cardiovascular drift is not a bad thing. It just happens, but it should be considered in the training analysis. Especially if your workouts are set at heart rate, cardiovascular drift and its side effects can be a bit misleading. There is not really much you can do about it. One option, especially if you are exercising indoors, would be to “cool” your body (e.g. with a fan) so that your body temperature does not rise too quickly.
A second measure would be to drink enough and stay hydrated to reduce cardiovascular drift. In order to optimise training, it would be a good idea to switch to wattage analysis (there are devices that make this possible for runners as well, not just cyclists).
The main point is that we only have a limited influence on the phenomenon of cardiovascular drift, so we just have to “take into account” that it exists and dissociate its influence on our training as much as possible by working with more objective parameters, such as strength (for cyclists and also runners) or speed on flat tracks for runners.