Tennis players have been known to incorporate unorthodox techniques into their training, but Serena Williams, on her comeback trail, has been taking things to the next level.

She demonstrated her athletic versatility in Spartan Races, but she's got a lot more tricks under her sleeve. The 23-time Grand Slam champion turned a side-to-side-movement drill into splits and cartwheel practice:

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"What an athlete!" wrote Patrick Mouratoglou, Williams' coach, on Facebook.

Williams is expected to play the Tie Break Tens exhibition in New York on March 5, and then she is scheduled to compete in her first post-pregnancy WTA event in Indian Wells.

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Two weeks ago, in her first official match back, Williams played a dead Fed Cup doubles rubber with her sister Venus, losing to The Netherlands in straight sets.

WATCH: Serena shows off cartwheel skills

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