The free and open-source MuscleMap extension can provide muscle segmentation: New extension: MuscleMap -- Automated Whole-Body Muscle Segmentation
We are working towards automated whole-body contrast-agnostic muscle segmentation for MRI and CT. The current model does not include the abdominal muscles, but we can work with you to develop a solution. Please feel free to reply to the MuscleMap extension in the new topic via the above link.
Also, feel free to suggest any new features that may be helpful for your needs. We are here to help!