ABSTRACT
How the cardiovascular (CV) system responds to exercise provides insight into the fitness and health of the system. For example, exercise blood pressure (BP) is an independent predictor of future BP[1] and the heart rate (HR) at a standard power output is frequently used as a measure of CV fitness, either by itself or after being converted into another index, such as predicted maximal oxygen consumption[2]. It has been shown that even in the early years of life, boys have lower exercise HRs than girls, implying that boys have better CV fitness[3]. It is not clear whether this is due to the boys having greater left ventricular (LV) dimensions (i.e. wall thickness, cavity size) or a greater functional capacity of some kind. The LV mid-wall shortening fraction has been identified as a valid index of LV function[4]. Since some studies have shown black children to have greater LV mass and different haemodynamic responses to exercise than white children[5], it is possible that ethnicity may influence these relationships.
