Stroke volume is the amount of blood in mL pumped out of the left ventricle of the heart per contraction. The stroke volume of each ventricle is often the same so that the right ventricle pumps the same amount of blood to the lungs as the left ventricle pumps to the body.Stroke volume’s immediate response to training is to increase. The average human has a stroke volume of around 70 mL, this volume can double during exercise at high intensities.
The graph on the right depicts the traditional findings in relation to the immediate responses to training for stroke volume. In this graph, the athlete’s stroke volume increases until it reaches around 40% VO2max or 63% MHR and then plateau’s throughout the remaining increase in intensity, leaving the increase in HR to provide the extra increase in cardiac output (volume pumped out of the left ventricle each minute) as required.
However, this is much more simplified than many of the findings in relation to stroke volume responses to training. This second graph from C A Vella and R A Robergs shows the large variety of immediate stroke volume responses to training.
The continuing rise in stroke volume for some athletes and not others has been attributed to a variety of variables including, sex, blood volume and fitness levels of the athletes. It is thought that the elite athlete is able to continue to increase their stroke volume through to their VO2max, while others cannot, but more study is needed.
The reason for stroke volume increase during training or exercise is threefold. Firstly there is an increase in blood returning to the heart due to muscular contractions, which naturally results in greater diastolic filling of the heart increasing the stroke volume. Secondly, the body has a higher demand for oxygen and therefore the heart contracts more forcefully during exercise. And thirdly, there is less resistance to the blood moving out of the ventricle due to vasodilation (widening) of the blood vessels.
References
C A Vella and R A Robergs. “A review of the stroke volume response to upright exercise in healthy subjects” British Journal of Sports Medicine 2005; 39 688-688.
Stella S. Vieira et al. “Does Stroke Volume Increase During an Incremental Exercise? A Systematic Review” Open Cardiovasc Medical Journal. 2016; 10: 57–63