Stroke volume

Stroke volume is the amount of blood the heart ejects with each beat, measured in milliliters.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 131.} Multiplying stroke volume by heart rate gives cardiac output.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 131.}

Stroke volume rises as exercise begins, then starts to plateau when oxygen consumption reaches about 40 to 50% of maximal oxygen uptake.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 132.} Sedentary college-aged men reach maximal stroke volumes of 100 to 120 mL per beat; women reach about 25% less because of smaller average body and heart size.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 132.} Training can raise those maximums to 150 to 160 mL for men and roughly 100 to 110 mL for women.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 132.}

More blood returning to the heart fills the ventricle further, stretching the heart muscle so it contracts more forcefully, the Frank-Starling mechanism.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 132.} Catecholamines such as epinephrine also strengthen contraction.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 132.}

In practice

Most of the training gain in cardiac output comes from stroke volume.^{3International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 208.},^{4Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 106.} Maximal heart rate is largely genetic and age dependent: it stays the same or dips slightly with training.^{3International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 208.},^{4Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 106.}

A larger stroke volume lets the heart beat less often while delivering the same cardiac output; the NSCA identifies a significantly lower heart rate at a standard submaximal workload as a hallmark of aerobic training.^{5Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 136.} The increase in stroke volume comes from a larger left ventricular chamber and wall, stronger contractions and greater blood volume.^{5Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 136.},^{3International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 208.}

Highly conditioned endurance athletes often have resting heart rates of 40 to 60 beats per minute, partly explained by moving more blood per contraction.^{5Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 136.}