I always thought it was mussel shoals like the bi-valve.
Several theories:
Just How Did Muscle Shoals Get That Name?
https://quadcitiesdaily.com/just-how-did-muscle-shoals-get-that-name/
There are several explanations as to how the city got its name. One is that it was named for a former natural feature of the Tennessee River, a shallow zone where mussels were gathered, and settlers named as Muscle Shoals. When the area was first settled, the distinct spelling of “mussel” to refer to the shellfish had not yet been locally adopted. Cherokee people called it, “the place of clams or mussels”.
Many Alabamians call it simply “The Shoals”.