Avoiding Miyako-jima Strongman crowds

Hi all :)
I am planning to spend two and a half weeks during april 2013 on Miyako island and the rest of april on Okinawa main island.
I have read, that on 21st april the Strongman triathlon is taking place on Miyako island with both Japanese and international attention.
As my aim is a relaxing time-out vacation and not so much following the triathlon, I am wondering of how to avoid the crowds best. Does anyone have experience if the spectators arrive (and the preparations begin) long before or if the island is rather crowded after the triathlon day? So basically should I plan the time on Miyako before or after the 21st, if I prefer a calm, remote atmosphere? (maybe also considering the beginning of the Golden week at the end of april?)
I�Ld be very happy about every idea.
Thanks in advance :)

Hi
Strongman Triathlon is 1500 athletes, coaches and all throughout the organization that goes with it. So there are many people on the island for more than a week.
The competition takes place Sunday, April 21, 2013.
Swimming takes place in the south of the island, between Yonaha beach and the village of Shimoji.
The bike is 1.5 times around the island and ends Hirara city field.
The foot race is a marathon of a loop around Hirara.
It is difficult not to be confronted with the event ... except for staying since before the golden week begins April 26 and ends May 6
Here are the main places of the island:

http://www.soleilrouge.org/blog/articles-cat-240173-674115-miyako_jima...

If you want more information, do not hesitate to ask questions.
Have a nice trip at Miyakojima!