My game only works to the degree I am able to move.

クルム伊達選手は女子ツアー最高年齢で全豪オープン三回戦へと駒を進めました。気温が４０度を越える中、ごりっぱです。

Tennis: Date-Krumm, Morita into Australian Open 3rd round

MELBOURNE (Kyodo) -- Two days after becoming the oldest woman in tennis' open era to win an Australian Open match, Kimiko Date-Krumm advanced to the third round of the tournament, joining Japanese compatriot Ayumi Morita.

The 42-year-old Date-Krumm defeated 25-year-old Israeli Shahar Peer 6-2, 7-5 to reach the third round at a Grand Slam for the first time since she was a Wimbledon semifinalist in 1996.

Date-Krumm won all four of her break points in the first set, and ran out a 3-0 lead in the second, before Peer, currently ranked 90th in the world, fought back to take a 4-3 lead. With the set tied 5-5, Date-Krumm broke Peer to take the lead and held serve to close it out.

"I enjoyed playing tennis today," said the 100th-ranked Date-Krumm, who in her prime was ranked fourth in the world. "It was tougher than my first-round match. My opponent, too, has been a big player, in the top 30."
"The heat was also a concern. My game only works to the degree I am able to move."

http://mainichi.jp/english/english/newsselect/news/20130117p2g00m0sp077000c.html

ここのMy game only works to the degree I am able to move.はどういう構造になっているのでしょうか。その意味は？Minnesotaくん、どうぞ。（UG）