In general, the heart rate is perfect for tests performed in the laboratory, where it shows a perfect correlation with the increase in external load (power produced). It is less perfect in testing for road practice, where it suffers from a series of limitations, consisting precisely of its response that is a little slow but also susceptibility to fatigue, altitude, coffee consumption and the time of day.
Threshold rate, training heart rate, anaerobic threshold rate, are concepts that have become part of the cycling jargon.
From the cycle computer to the heart rate monitor
Heart rate: where it doesn't work
It is clear, therefore, that in this case one could not rely on the heart rate to regulate the intensity of the effort.
Heart rate: where and how it works
If, for example, at the beginning of training you wanted to immediately reach the zone of medium-high intensity (corresponding, for example, in the case of a certain subject to 150 beats), you would start the training by pushing too hard and finding yourself pedalling at an intensity higher than needed, because the heart needs time to increase its frequency. In addition, the heart rate has daily variations that depend on the stages of shape or fatigue.
The arrival of power sensors
Ultimately, the heart rate is therefore influenced by so many factors that many athletes, when they train or when they compete, prefer not to know it, because it could be misleading, and focus on the perceived effort.
Heart rate limits include susceptibility to fatigue, altitude, coffee consumption, time of day, etc.