1. I read it as "overuse increases the chance of getting injured".
2. See second definition:
sit something ↔ out phrasal verb
1 to stay where you are and do nothing until something finishes, especially something boring or unpleasant : She had two weeks to sit it out while she waited to hear if she had got the job.
She was prepared to sit out the years of Jack’s jail sentence.
2 to not take part in something, especially a game or dance, when you usually take part : Johnson sat out the game with a shoulder injury.
(Longman Dictionary of Contemporary English)
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