Here is an explanation of the difference between two similar (but very different) fitting options – muscle fit vs slim fit.
What size slim fit shirt would equal a regular shirt? - Quora
Men's fitted shirts. See our comparison for the Tapered fit to
What Are Muscle Fit Shirts vs Athletic Fit Shirts vs Slim Fit
Slim Fit vs Fitted: Who Are They for? - TAILORED ATHLETE - USA
Slim Fit vs Athletic Fit (A Battle of the Styles) - TAILORED
Slim Fit vs. Tapered Fit vs. Relaxed Fit: What's the Difference?
What does 'slim fit' actually mean? - Hockerty
Muscle Fit vs Slim Fit - the Difference Tailoring Makes - TAILORED
Slim Fit VS Standard VS Athletic Fit Dress Shirts
Muscle Fit vs Slim Fit Shirts – What's the Difference? – Tapered