Explanations of stroke volume increase
Recall that heart rate increases with exercise intensity in cross-country skiing. With the increasing work rates approaching maximum heart rates in cross-country skiing, the diastolic filling time could be shorted enough to limit filling. As a result, end-diastolic volume might plateau or decrease.
Although there is agreement that stroke volume increases from rest to exercise, until recently just how this increase occurs was not well documented. One explanation is the Frank-Starling law, which states that the primary factor in controlling stroke volume is the extent that the ventricle stretches. When the ventricle stretches more, it will contract with more force. For example, if a larger volume of blood enters the chamber when your ventricle fills during diastole, the ventricle's walls will be stretched more than when a smaller volume enters. In order to eject the greater amount of blood, your ventricle must react to this increased stretching by contracting more strongly. This is referred to as the Frank-Starling mechanism.
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| Olympic cross-country skiers can continue to increase their stroke volumes after exceeding the 40% to 60% V02 max level, perhaps because of adaptations to training. |
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