Used a collection of 1000 real muscle-girl images from the web.

V1 uses SDXL - illustrious-realism-by-klaabu as the base.

V2 uses SDXL - Ilustrious as the base

The goal of this model is to create muscle girls / fitness girls with realistic bodies.

V1 results are okay-ish. The realistic models + high values of the LoRa can give weird faces and missing arms. Lower values can work and zoomed in pictures can also work. Full body distant shots, not so much. If you use illustrious-realism-by-klaabu, try 1024 x 1536 with 0.25-0.4 scale for best results.

V2 results are better. This version generates fairly realistic muscular bodies. It cannot generate extremely muscular or large shapes, but can easily be mixed with other models. Adding more muscle focused models quickly adds a lot of muscle mass.

Non-realism models seem to work better, even with higher values (see examples). If the model is turning your results too realistic, use "realistic" in the negatives.
In any case, use the prompts + dimensions of the original model you are using and add the prompts described below for best results.

TAGS
Use the tags like "muscle girl" or "muscle-girl", "extremely muscular" , "female muscle" ,"muscular", "pose", "flexing" to generate more muscular girls. Some poses like "hands on waist" or "hands on hips" are over-represented in the dataset, so use them as negative if you don't want that.

A lot of the images are selfies, so tags like "cellphone", "holding phone", "selfie" will lead to a selfie.

Additionally you can try specific muscles like: "bicep, biceps, triceps, triceps, latissimus, latissimus dorsi, back muscles,trapezius, delts, deltoid muscle, abs, abdominals, obliques, quadriceps, calves, glutes, gluteal muscles, pecs, pectoral muscles"