"get into shape" is correct and usable in written English. You can use it to refer to an activity that someone does to make their body healthier, such as going to the gym regularly. Example: "I'm determined to get into shape this year by exercising at least three times a week.".
"To get into shape".
"I got to get into shape.
I'd done all I could to get into shape.
"That's nothing until I get into shape," Rodman said.
She also hopes he will get into shape.
"But it's going to be longer to get into shape".
Some players are motivated to lose weight and get into shape.
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