While you may only know Pippa Middleton as the sister of Kate, the Duchess of Cambridge, she's also an endurance athlete—and she's using her talents for a good cause.

On Saturday, Pippa and her brother James joined nearly 300 other cyclists at the start of Race Across America, a 3,000 mile charity bike ride from San Diego to Annapolis, Maryland. They'll travel through 12 states in 8 days, and will need to cover 350-500 miles per day. The Middletons, along with their 6 teammates, are raising money for the British Heart Association, for which Pippa is an ambassador, and the Michael Matthews Foundation, an educational charity.

It's a seriously impressive challenge, though it's not entirely surprising for a woman who, in 2011, finished a grueling Scottish race called the Highland Cross, which consists of a 20-mile run followed by a 30-mile bike ride.

After finishing the event, she'll auction off her bike on eBay. And, according to her JustGiving fundraising page, she and James will travel to Istanbul in July to take on the Bosphorus Cross-Continental Race Swimming Race: a 6.5-kilometer swim across the Bosphorus Strait that starts on the European side of Turkey and finishes on the Asian side. We're tired just reading that.

If you'd like to break a sweat for charity, check out these 10 Bike Races for a Good Cause.

The Protein Smoothie Jennifer Lopez Drinks Every Day
5 Exercises From the President’s Leaked Workout Video
The Move Alicia Keys Does to Get Those Amazing Abs