Help him in seating down
give them glucose, if they have it
If they don't have it, let them consume anything sugary-juice, sugar loaded water, candies
Monitor the sugar levels and If the situation does not improve, call the hospital and ask for an ambulance.
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.
it's the circulatory system,the heart and blood vessels