[joecrisp]

Swimming and cross-country skiing are probably two of the best cardio exercises in terms of burning calories and improving cardiovascular condition. Obviously, most of us won't be able to do much cross-country skiing, but the cross-trainer machines I spoke of in a previous post simulate the action of cross-country skiing, providing resistance to both the upper and lower body, much in the way that swimming does.

Another great benefit of swimming and using cross-trainers and other elliptical machines, is that they are zero-impact activities, meaning there is no stress on the joints due to impact on a surface, which is one of the major drawbacks of running and other aerobic activities.

As an indication of how beneficial swimming and cross-training can be for the heart, some of the lowest resting heartrates ever recorded in healthy humans have been those of Olympic-class swimmers and cross-country skiers. These athletes have been known to have resting heartrates in the 30s! As a comparison, a resting heartrate of 60 is considered healthy for most humans. Resting heartrate is an indicator of the strength and efficiency of the heart and cardiovascular system. The healthier that system is, the less beating the heart has to do, since the heart muscle is stronger and capable of pumping more blood per beat, and the vascular system is capable of transporting blood and oxygen more efficiently throughout the body.