Source: Unearthed Arcana 38 - Feats for Skills

You become stronger, gaining the following benefits:

• Increase your Strength score by 1, to a maximum of 20.

• You gain proficiency in the Athletics skill. If you are already proficient in the skill, you add double your proficiency bonus to checks you make with it.

• You count as if you were one size larger for the purpose of determining your carrying capacity.