The Chihuahua breed of dog is not a very active breed of dog. While some dogs like to work and run and play, the Chihuahua would prefer to just lay around and sleep. Weight can be a big issue with this breed of dog because of their inactivity.
The key is to not overfeed them. I do have a self feeder but it isn't filled and is only down from the time I leave to go to work until I get home. My Chihuahua gets a little soft food mixed with hard food at dinner time and she gets a treat before bedtime.
A lot of people tend to over feed them with giving them table food. We feed our girl while we are eating. She is less likely to set up pretty and beg at the table which is why we do that. An overweight Chihuahua can develop problems with their patellas (knees). It also isn't good for their heart to be overweight.
A Chihuahua who has been neutered or spayed or an older Chihuahua tends to just want to lay around. My Chihuahua is spayed and she isn't what I would call old..er (Chihuahuas can live into the teens) she is seven so she is middle years.
She goes on walks with us and when we are outside, she is outside to try to keep her a little active. She weighs six pounds which is the normal weight for a Chihuahua.