Stroke volume is termed the amount of blood that is pushed out of the
ventricles of the heart with each beat.
A normal range of values at rest is between 60 and 130 ml per beat.
These amounts can increase to between 150 and 180 ml per beat during exercise.
These values refer only to the blood that is pumped out of the left ventricle.
An equal amount of blood will simultaneously be pumped out of the right
ventricle.
Stroke volume increases with endurance training. Many factors contribute
to the increase, including increased strength of the cardiac muscle fibbers,
an increase in ventricle size, and a decrease in the thickness of the blood. The
stroke volumes of athletes are usually greater after training than before,
which explains why they have a lower resting heart rate. They can supply the
same amount of blood to their bodies by pushing more blood out of their hearts
with each beat; therefore, their hearts do not need to beat as fast. For the
same reasons, training will also reduce the heart rates of athletes by 10 to 15
bpm during identical submaximal swimming efforts. Training will also increase
the maximum stroke volumes that athletes can attain. Maximum values may be in
the range of 120 to 140 ml per beat for the untrained person, but it can
increase to between 160 and 180 ml per beat after training.
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