Caitlyn Jenner struggles with sports bras in new I Am Cait teaser

Caitlyn Jenner looks as happy as ever playing tennis in the new teaser for her E! docu-series, I Am Cait.

Watch above as the former Olympian realises the importance of sports bras! And just how toned are those legs? Not bad at all for a 65-year-old.

We also get to see Caitlyn switching up her hairstyle, partying with friends and bonding with her 89-year-old mother Esther and stepdaughter Kim Kardashian.

Caitlyn is about to have another big moment on Thursday, accepting the Arthur Ashe Courage Award at the 2015 ESPY Awards (Excellence in Sports Performance Yearly) in Los Angeles.

All of her 10 children and stepchildren are expected to attend, along with Caitlyn's sister and mother.

We wonder if ex-wife Kris Jenner will make a surprise appearance with boyfriend Corey Gamble?

I Am Cait premieres in Australia on Monday, July 27 at 9.30pm on E!