Your functions and blood are all moving by the force of gravity, so when everything is raised or lowered(moving your arm), your pulse wave changes. This can also result from subtlty in higher blood pressure, when activity occures. Just as your pulse waves changes in the rest of your body when excersising, you will have a slight change in pulse when simply moved your arm up and down, you're gettin' that blood pumping! ;)
Hope this helps :)
MEDICAL..............
explainzzz
They must share the same domain
Explanation:
I guess Muscle strength and endurance then there is Cardiovascular Endurance that can help. Flexibility not so much. Body composition helps very much.
Answer:
My final answer would be Body Composition. Nothing else matters that much. In order to swim you need to use to use your body.