What activities raise fitness skill but do not make you more muscular or thinner?

Other than fitness books, all fitness activities will eventually cause you to lose weight, gain muscle, or both. I would suggest a gradual approach. Jog or use the treadmill interspersed with eating lobster thermidor (preferably two or more helpings at a time).

I usually have my sims jog but not every day, just enough to keep them in shape.

Fitness books, attending a skill class at uni or if your sim is in uni doing fitness as an elective. I don’t think swimming affects the sims body size too much.

Several years ago I saw a list someone made.

Supposedly, swimming, tv work outs, jogging and treadmill burn fat but don’t create muscle.

Weight machines and basketball supposedly build muscle.

Rock climbing and boxing supposedly build muscle and help you lose fat, and back then yoga was on this list too.

Horseshoes and dancing supposedly have no effect.

High protein plate helps you bulk up.

The List was created before discover university.

Your sim can also lose or gain weight eating the thin, or weight gain ice cream in cool kitchen stuff. My sims have even take em other sims out to restaurants and ordered one or the other for unplayed sims and the sim that ate it either lost or gained weight.too

If you sim was given the active sim trait then they have high metabolism and burn calories faster.

I don’t know what biking, playing kick the soccer ball ( discover university ), or what sparring with someone or using the sparring machine ( strangerville ) do. I have heard different things about yoga. I have wondered myself what these activities do.

I think if a sim walks a lot, ( or walks an animal ) that it should help them slim down too, but I have never seen anyone say it has any affect so I guess it doesn’t.

I don’t know how accurate this list is as I got it from someone else who compiled it years ago, but I do have 1 female sim who has used the treadmill and jogs every once in awhile with the active trait ( high metabolism ), that doesn’t bulk up or gain weight, she also does one of the tv workouts. I have another female sim without the active trait that jogs sometimes, she usually doesn’t gain weight, unless I don’t play her for a long time. I play rotationally. I have an adult male and female sim that don’t do any athletics and sometimes eat low calorie, and sometimes eat high calorie foods, and they have both gained weight. I have one male sim that has the active trait ( also has an athletic job ) works out on a machine ( occasionally) at the gym, and eats high protein drinks and jogs occasionally, and he is very bulky. I have an astronaut that boxes and is muscular, but not bulky….. for what this is worth. There are lists out there about what ( for sims ) are high calorie foods and what aren’t.