Answer: Heart rate response
Step-by-step explanation:
The idea to train heat is important for the normal functioning of heart. It trains the heart by pushing it towards its limits.
In normal person without any kind of medication, the heart rate is based on the age. According to that the training mode is decided.
But in case the person is taking any kind of medication which alters the heart rate, then hear rate response is used to decide the training of heart.