Variations in Heart Rate

Variations in Heart Rate

  • The resting heart rate is usually between 60-100 beats per minute (bpm), but highly trained athletes may have slower rates.
  • Heart rate can also be influenced by factors such as stress, anxiety, hormones, medication and the level of physical activity.
  • While the heart operates on its own intrinsic rhythm, it responds to the body’s demand for oxygen and nutrients by varying the heart rate.

Control of Heart Rate

  • The heart rate is controlled by both the nervous system and the endocrine system.
  • The autonomic nervous system regulates the heart’s speed. This system has two divisions: the sympathetic and parasympathetic nervous system.
  • The sympathetic system stimulates the heart to beat faster, whilst the parasympathetic system slows it down.
  • The medulla oblongata in the brain has centres that regulate the rate of heart beat: the accelerator centre and the vagus centre.
  • Adrenaline (epinephrine), a hormone produced by the adrenal glands, can also increase heart rate.

Sensing Heart Rate Variations

  • Baroreceptors are pressure sensors located in the aorta and the carotid artery. When blood pressure rises, these receptors send signals to slow down the heart rate.
  • The amount of carbon dioxide in the blood can also affect heart rate. High concentrations can speed up the heart rate, while low concentrations can slow it down. Respiratory centres in the medulla oblongata send signals via the nervous system to adjust heart rate accordingly.
  • Chemoreceptors, sensitive to changes in chemical composition of the blood, particularly pH and carbon dioxide levels, send signals to the heart to adjust beating rhythm.

Exercise and Heart Rate

  • Exercise increases the need for oxygen in muscles, leading to an increase in heart rate.
  • Heart rate increases proportionally to the intensity of the exercise due to increased metabolic need.
  • Regular exercise improves cardiovascular health by lowering resting heart rate, as the heart becomes more efficient at pumping blood.
  • Drawing a graph of heart rate against time can be useful in analysing the effect of different durations and intensities of exercise. This is known as a heart rate performance curve.

Monitoring the Heart

  • Heart rate can be monitored using a heart rate monitor which often comes built into fitness trackers or smart watches.
  • These monitors can provide real-time feedback, allowing the users to adjust the intensity of their workout.
  • They can help in developing an optimal exercise program that maximizes cardiovascular fitness, fat burn or endurance.