• In healthy, sedentary subjects, the training- induced improvements in VO2 max occur due to both increases in maximal cardiac output (i e, stroke volume increases) and an increase in the a v o2 difference.
• The training-induced increase in maximal stroke volume is due to both an increase in preload and a decrease in afterload.
a. The increased preload is primarily due to an increase in end diastolic ventricular volume and the associated increase in plasma volume.
b. The decreased afterload is due to a decrease in the arteriolar constriction in the trained muscles, increasing maximal muscle blood flow with no change in the mean arterial blood pressure.
• The training-induced increase in the a-v O2 difference is due to an increase in the capillary density of the trained muscles, which is needed to accept the increase in maximal muscle blood flow. The greater capillary density allows for a slow red blood cell transit time through the muscle, providing enough time for oxygen diffusion, which is facilitated by the increased number of mitochondria.