Because cross country skiing engages about all of the major muscle groups in the body, cross country skiing is an excellent method of training for physical fitness and dynamic muscular endurance.
Cardiac output is a function of stroke volume, the amount of blood the heart pumps in one beat.
The pericardium is a non-elastic sack around the heart that may limit maximum filling. The lungs could also be a limiting factor in cases of disease, altitude, or possibly at very high work loads. Maximal Oxygen Uptake Oxygen consumption is considered the standard for measuring the physiological intensity of exercise. If heart rate is the tachometer, then oxygen consumption is how much gas per mile you're burning to achieve a certain speed. In cross-country skiing, success is largely dependent on the body's oxygen uptake ability.