Swimming

Question

Regarding your response of "for what purpose is surfing done"? It is an art or skill. Just like a person plays basketball a person goes surfing, but this is done in the water. I saw a person asked if it's permitted to swim in the 9 days for exercise and you replied " Yes even just to cool off from hot weather". I would just like to know if this type of action can be done during the 9 days? How would this be different? Thanks.