Triathlon champion reveals top tips
More than a thousand of you will be having a very energetic weekend, taking part in the world's largest ever Junior Triathlon.
The event takes place at Hever Castle in Kent and 1300 of you are expected to be taking part.
During a triathlon athletes have to swim, cycle and run - it's very tiring and takes a lot of strength.
Britain's Non Stanford - the ITU World Triathlon champion, gives Newsround some tips ahead of the event.