Natural Heavyweight( Planar Handbook, p. 40)
You are descended from creatures native to a plane of heavy gravity. On planes with normal gravity, you feel light and buoyant.
Your carrying capacity is doubled. Double the values given in Table 9—1, page 162 of the Player's Handbook, to determine what your light, medium, and heavy loads are.
On a plane with normal gravity, you gain a +2 circumstance bonus on Climb and Jump checks, but you also take a —2 penalty on Balance, Ride, Swim, and Tumble checks. On a plane with light gravity, these bonuses and penalties are doubled (and replace the normal bonuses and penalties on these skill checks).