The training pulse varies within a workout
It's a well-known phenomenon. With consistent efforts, the heart rate often rises during a session. And that even though you don't change the load. Figure 1 shows one of these examples from a small study. During a steady bike ride at 180W, the heart rate rose from initially measured 125 bpm to 140 bpm after 60 minutes. That makes a 15 stroke difference, 12.3%!
Figure 1: Course of the training pulse over 60 min at a constant 180W
Anyone who is now looking for their fat-burning pulse should realize that 15 beats definitely make a difference! Conversely, if you train very strictly on your fat-burning pulse, you would have to accept that the pace and load would have to be reduced more and more in order to hit the target fat-burning pulse range (as in Figure 2).
Figure 2: Drop in performance with a constant fat-burning pulse
But can that make sense? No Apart from the fact that it's probably no fun to run slower and keep looking at the clock, it's much more about setting the right exercise intensity for optimal fat burning. And the heart rate, as a “passive load parameter,” is not the appropriate variable here. Instead, it makes more sense to set and then maintain a PACE or a subjective sense of stress. It is not only useful that the organism adapts to the situation and reacts to the load at a corresponding different heart rate, but also completely normal.
There is therefore no ONE FAT-BURNING PULSE, but this value fluctuates from training to training and even within a session. There is another example of this here...