I am a very petite woman, weighing almost 80 pounds. I don't have an eating disorder and am healthy. Would a school not allow me to complete fieldwork because of this?
I don't think that would be an issue. Like @Bokonomy said, programs will teach you proper body mechanics and how to do transfers. I am also petite, but I worked at a rehab clinic prior to starting grad school, and the therapists taught me so much to prevent injuries.