big fellow wrote:
Here's my take on it:
3) Swimming is the lowest because the water supports your body weight. You just have to provide the motor. Also, the water cools your body, which naturally slows the heart rate, as the body does not need to pump blood to the skin/external layers in an effort to cool itself.
Incorrect I am afraid - research on water polo players and swimmers shows that their sweat rates can be similar to those of land based sports. Your core temperature certainly increases and blood to the peripheries (including skin) is vital to keep you cool....
The contact with the water certainly aids regulation of body temperature but the body temp will still rise, and sweat glands cant tell whether your skin is already wet or not...
The difference in HR is pretty much only due to the muscle mass involved with each activity.
Running has the highest muscle involvement of all sports, AFAIK the only sport that comes close is rowing. Running is also a full weight bearing activity.
Cycling uses many muscle groups, but not as many and not as intensely as running. It is also not really a weight bearing exercise (no matter how sore your arse may get after 100km!). Coasting is the perfect example of this.
Swimming uses much fewer muscle groups/muscle mass. The bodyweight is virtually completely supported during swimming. Think about muscle size in your arms compared to muscle size in your legs.
**edit: cross country skiing is equal to or greater than running. (Sorry, this sport doesn't cross my mind too much coming from Australia!)