You have undergone extensive physical training to gain the following benefits:

• Increase your Strength or Dexterity score by 1, to a maximum of 20.
• You don't become flatfooted when standing up while prone.
• You may now use Acrobatics instead of Athletics for checks that don’t involve strength beyond ones’ own body weight; e.g. swimming, jumping, climbing. Checks made where then there is weight bearing beyond body weight; grappling, lifting, pushing, pulling, would not apply. 

Inspired by and based upon KG123's Agile Athlete.