Increased heart rate during exercise is brought about by which of the following?

The increase in heart rate during exercise is primarily due to the sympathetic action of the autonomic nervous system. When engaging in physical activity, the body requires more oxygen and nutrients, which are delivered by an increase in cardiac output. The sympathetic nervous system, part of the autonomic nervous system, gets activated in response to exercise. This activation releases neurotransmitters like norepinephrine, which stimulate the heart to beat faster and with greater force, effectively increasing heart rate.

In addition, the sympathetic nervous system prepares the body for 'fight or flight' responses, enhancing overall physical performance during strenuous activities. This mechanism ensures that sufficient blood reaches the muscles and vital organs, facilitating improved endurance and strength during exercise.

Other options refer to the parasympathetic system or somatic nervous system, which do not play a direct role in increasing heart rate during exercise. The parasympathetic system is generally associated with 'rest and digest' functions, opposing the actions of the sympathetic system. The somatic nervous system primarily governs voluntary muscle movements and is not involved in the automatic regulation of heart rate during physical activity.