Now we know exactly why Serena Williams showed us her workout regimen in fleeting video clips and images on social media in July. She was sweating—not to the oldies, but to Jay Rock's "Pay for It" featuring Kendrick Lamar and Chantal—for a new Beats by Dre commercial. The clip also features Alex Ovechkin, Maria Kirilenko's former fiancé; LeBron James; Zou ShiMing; and Cam Newton.

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​In the one-minute piece, Serena shows off her abs with some medicine-ball work, performs the splits, practices her footwork, and more. It's all for the benefit of the brand's Powerbeats2 Wireless ​rollout, and suffice it to say, Serena turns it out in both perspiring and inspiring fashion.

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