"도장에 나가 몸이라도 구르는 것이" => (if nothing else / perhaps) even going to the gym and doing rolls and tumbles. It is just a noun phrase, needing the predicate part to complete the sentence. Also, the sentence is not a perfect one grammatically. it sounds odd because the verb connective form -아/어 can't have a new subject following it as in 나가 * 몸이라도. 몸이라도 itself can be either the subject or object of a verb, but 구르다(roll, tumble) being an intransitive verb makes it the subject. To be grammatically correct, it should be written as 도장에 나가 (몸)구르기라도 하는 것이, but the original sentence sounds more effective as far as the intended meaning. This is an odd example of pushing the boundary of grammar. I don't know if that grammar oddity is what gave you the difficulties, but you can ask again if you have further questions.

도장 - gym or training hall especially for martial arts like Taekwondo or Kendo. 몸이라도 구르는 것- doing some basic excersise like forward roll or backward roll. If it is 몸이라도 "굴리는 것", the meaning could be totally different. In that case, it means doing hard and physically painful workout or having somebody do hard physical activities, excersise or work.