Tack that's adjusted too tightly can compress the skin. Transmitted through the skin, pressure impacts underlying tissues and structures, and the compression can result in a lesion. For example, a girth must be snug enough to keep the saddle in place, but not squeeze the skin too tightly. If it rubs the skin excessively, the pressure can produce a friction sore. A girth can be too loose, so it rotates.
Movement causes rubbing and leads to a girth gall.
A girth gall abrasion can make the horse reluctant to move forward. Tomlinson explained the benefit of the string girth. It moves with the skin. It gives, and it doesn't bind. String girths traditionally were made of cords of mohair wool, although most today are a blend of mohair and rayon.