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• Starling's law


  The principle that stroke volume is equal to venous return
• Starling's law has nothing to do with little speckled birds
• Venous return


  The amount of blood returning to the heart, specifically the right atrium
• Mechanisms to increase venous return during exercise

  1. Gravity

  2. Smooth muscle pulsing in veins

  3. Pocket valves in veins

  4. Skeletal muscle pump

  5. Respiratory pump
• Gravity

  Helps blood return to the heart depending on body position
• Smooth muscle in veins

  Can pulse to increase blood pressure and reduce vein lumen, supporting venous return
• Pocket valves in veins

  Prevent backflow of blood, maintaining one-way flow towards the heart
• Skeletal muscle pump


  Contraction of skeletal muscles surrounding veins squeezes blood back towards the heart
• Respiratory pump


  Changes in thoracic cavity pressure during breathing help draw blood back to the heart
• The more intense the exercise, the more the respiratory pump mechanism operates to increase venous return