We had a wish of studying the changes in stroke volume during incremental exercise, to see what effect it has on the increasing cardiac output; if the stroke volume would continue to rise, reach a plateau, or decrease. In addition we wanted to evaluate the methods used to obtain these results.
We performed a literature study by searching in PubMed using Reference Manager 11.0 .The words used were: `stroke volume AND physical activity`, `stroke volume AND exercise`. This yielded 64 relevant articles of which 23 were included in the study based on inclusion and exclusion criteria.
A table was made to shows the interesting findings. We also made graphical illustrations to displays the connection between 2 or 3 variables to look for any correlation. Substantial variation between the articles both in quality, results and methods used we found. In our material 6 articles showed a tendency for increasing stoke volume, 18 reached a plateau phase while 5 decreased, even though the cardiac output continued to rise until maximal exercise. There was no connection between stroke volume and: 1) the method used, 2) publishing date of article, 3) position of study object, 4) training level among study objects.
Many different theories have been used to explain the changes in stroke volume. The most frequent are: increased preload and the use of Frank Starling, increased contractility, or reduced afterload. These may be used in various ways and in combination.
There are no studies with high enough quality, and frequent measurement at high intensity to draw any conclusion about the changes in stroke volume during incremental exercise. The results are also inconclusive. To obtain an adequate answer to our quest, more research is needed.