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Cardiac Output. “So you want to be a marathoner?”. Do you have the blood for it?. “Q” In The Untrained Person. In the average person, a 5-L cardiac output is usually sustained with a heart rate of approximately 70 beats a minute.
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Cardiac Output “So you want to be a marathoner?”
“Q” In The Untrained Person • In the average person, a 5-L cardiac output is usually sustained with a heart rate of approximately 70 beats a minute. • Stroke volume and cardiac output for women usually average approximately 25% below the values for men. • This “gender difference” is essentially due to the smaller body size of the average women. • Stroke volume is about 70ml at rest.
“Q” In The Endurance Athlete • Endurance training causes the sinus node in the heart to come under greater control from the parasympathetic nervous system. • At the same time there is probably a reduction in the sympathetic activity. • When the heart slows due to the parasympathetic influence, this is called “vagal” tone. • Stroke volume may be 100ml at rest for the athlete.
Heart Rate During Exercise • The large stroke volume of an endurance athlete is accompanied by a heart rate reduction during submaximal exercise.
Distribution of Cardiac Output • At rest: approximately 1/5 of blood flow is directed toward muscle tissue. • The majority of blood is directed to the digestive tract,liver,spleen,brain and kidneys. • During exercise: the major portion of the cardiac output is diverted to working muscles. • Some tissues can handle a temporary reduction in blood during heavy exercise. • Example:blood flow to skin increases with light/medium exercise but decreases with heavy exercise.
Blood Flow to the Heart and Brain • Some tissues cannot compromise their blood flow. • The myocardium uses about 75% of the oxygen flowing through the coronary vessels at rest. • A large increase in heart rate during exercise, is accompanied by an increase in coronary circulation. • This increase is up to 1 liter of blood per minute. • Cerebral blood flow is also increased by up 30% compared to resting conditions.
Extraction of Oxygen: A-V 02 Difference • At rest: about 75% of the blood’s original oxygen load is still bound to hemoglobin after it makes the complete tour through the body. • After training: up to 85% of the oxygen is removed from the hemoglobin during exercise. • But only in the specific muscle fibers used during exercise. • This is due to increased capillaries, mitochondria and aerobic enzymes.
Cardiovascular Adjustments to Upper Body Exercise • Maximal oxygen uptake during exercise with the arms is generally 20-30% lower than exercise with the legs. • Maximal heart rate is also much lower with arm work. • What is the reason ? • Relatively smaller muscle mass involved.
The Athlete’s Heart • Cardiac hypertrophy results from individual myofibrils thickening and from an increased number of myofibrils. • This is viewed as a fundamental adaptation to an increased work load. • In endurance athletes the heart may be up to 25% larger. • Not sure if this is genetic endowment or training induced or both.
Shot Putter vs Runner • “Isometric” athletes like wrestler, lifters have larger muscle mass, especially the intraventricular septum. • Lifters heart may weigh 330grams and have left ventricular volume of 110ml. • Runners heart may weigh 308 grams and have left ventricular volume of 180ml. • Non-athletic heart weighs 211 grams and has left ventricular volume of 101ml.
