What happens to the heart rate during physical exercise?

During physical exercise, the heart rate increases as the body demands more oxygen-rich blood to support the working muscles. This increase is mediated by the autonomic nervous system, specifically through sympathetic stimulation, which enhances heart rate and contractility. The physiological response involves several mechanisms: the body's metabolic demands rise, requiring enhanced delivery of oxygen and nutrients. To accommodate this, the heart pumps faster (increased heart rate) and often harder (increased stroke volume) to meet the heightened circulatory needs.

As activity levels increase, so do the levels of circulating catecholamines (such as adrenaline), which further facilitate increased heart rate. This response is essential for maintaining physical performance and ensuring that the body's metabolic processes can be sustained during exercise. In contrast to the other listed options, which suggest a decrease in heart rate, constancy, or irregularity, the typical and expected outcome during exercise is a clear, measurable increase in heart rate.