Answer:
An individual's heart rate is changed or gets fluctuated due to his or her change in physical activities. This is due to the fact that with an enhancement in the physical activity, the demand for oxygen in the blood and in the body upsurges. As more energy is discharged, thus, more oxygen is required. In order to provide more oxygen to the blood, the heart is required to pump more blood in and out, which results in an increase in the heart rate.
