In a healthy human being, the increase in heart rate from rest to around 100 to 110 beats per minute at low intensity exercise is due to withdrawal of the parasympathetic nervous system's influence. If exercise intensity increases beyond that point, the matching increases in heart rate above 100 to 110 beats per minute are due to sympathetic nervous system influence.
There is a transition range around 100 to 110 beats per minute where the intrinsic rate of the heart beat is determined by the body's metabolic activity.
However, when a person takes a beta blocker, the sympathetic influence on the heart rate is attenuated, so that the person's max heart rate is lowered to around 110 beats per minute.
What is driving the heart rate at high intensity exercise in patients who take beta blockers? Is the heart rate around 110 beats per minute in patients on beta blockers driven primarily by the metabolic influences in the blood? What other factors are influencing heart rate around 110 beats per minute in patients who take beta blockers?