Serena Williams has been working hard in the gym over the last 12 months as she looks to keep herself in top physical shape despite retiring from tennis three years ago

Before hanging up her tennis skirt, Serena has been documenting her weight loss progress since giving birth to her daughters, Olympia, 7, and Adira, 1, who she shares with husband Alexis Ohanian, 42. RELATED: Serena Williams shows off incredible post-retirement body: See pics!

Serena Williams is proving that retirement hasn't meant slowing down, especially when it comes to fitness. The tennis legend, with an impressive 23 Grand Slam titles under her belt, hung up her racket after a gripping final match at the U.