Fitness (attribute)

In The Sims, a Sim's body type was fixed, and wouldn't change no matter how much s/he worked out or ate. The Sims 2 changed that by introducing a fitness scale which appears on the Simology panel. Sims in The Sims 3 also have a fitness scale, but it is not shown in the interface and a Sim's body shape changes gradually.

Sims can become fatter by continuing to eat after their Hunger bar is full, or become thinner by doing most things that increase the Body skill. If they gain or lose enough fitness, their body shape will change. Sims can increase fitness by swimming or working out on a community lot, even if they are not gaining Body skill.

Children can gain fitness by playing on swings, or jumping on the bed, though those activities don't seem to build Body skill. (This may depend on which expansion packs are installed.)