Nike Training Club releases Serena Williams workout

Fans of the Nike Training Club app can tap into a new workout starring tennis pro Serena Williams, who shares some of her favorite moves for developing a seriously ripped core.

"Core is incredibly important to my tennis game," says Williams. "Having a strong, stable core is key to many of the movements I have to make on the court, and the core in general is the foundation for a lot of my strength."

Geared for women, the 15-minute core workout is designed to tack on after running or cycling or a cardio class, or another Nike Training Club app workout, Nike says.

Other stars in Nike's corral to appear in upcoming monthly segments include gymnast Gabby Douglas, surfer Lakey Peterson, and track and field star Carmelita Jeter.

Announced this weekend, the Nike Training Club app has also received an update, which includes an approximate NikeFuel count and calories burned for every workout.

The app -- free for both iOS and Android devices -- includes more than 115 workouts including 120 drills that build on the fundamentals of strength, cardio, and core training.

Last month, Reebok launched a brand-new mobile fitness app for five workout disciplines -- walking, running, dance, yoga and strength training. App users can establish fitness training programs from six to 12 weeks, customizing routines using a variety of workout plans, such as mixing running with yoga. Plus you can access videos and demos, receive workout reminders, and share accomplishments with your social media.

Watch a trailer for the Serena Williams workout: