Physical exercise increases the heart rate because the working muscles require more oxygen to produce the energy required to sustain that physical activity. Healthy Living at AZ Central explains that the heart pumps the blood faster to supply the extra oxygen needed through the bloodstream.
Healthy Living at AZ Central notes that heart rate is regulated through the autonomic nervous system; this part of the brain is responsible for controlling the involuntary functions of the body, such as digestion and respiratory rate. As the intensity of physical exertion rises, the autonomic nervous system starts receiving signals to increase the heart rate from various parts of the body. Some of these signals come from the motor cortex and the movement-sensing receptors in the exerted muscles, as they perform the physical exercise.