Cardiac output

Cardiac output is the amount of blood the heart pumps each minute, measured in liters.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 131.} It equals stroke volume, the blood ejected per beat, multiplied by heart rate.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 131.} At rest, cardiac output is about 5 L/min; during maximal exercise, it can reach four times that, 20 to 22 L/min.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 132.}

When a client moves from rest into steady-state aerobic exercise, cardiac output rises quickly, then more gradually before leveling off.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 132.} Skeletal muscle receives 15 to 20% of cardiac output at rest and up to 90% during vigorous exercise.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 134.}

In practice

Aerobic training increases maximal cardiac output mainly by increasing stroke volume; maximal heart rate stays the same or drops slightly.^{4Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 106.} Maximal cardiac output tracks closely with VO2 max: higher output accompanies higher maximal aerobic power.^{4Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 106.}

At rest and at a fixed submaximal workload, cardiac output stays about the same or dips slightly after training.^{4Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 106.} The client delivers that flow with a lower heart rate and a larger stroke volume.^{4Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 106.}

The NSCA calls the rise in maximal cardiac output the most significant cardiovascular change over 6 to 12 months of aerobic training.^{5Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 136.} IPTA also lists higher cardiac output among the adaptations to a prolonged cardiorespiratory program.^{6International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 64.}