I got this shirt for my husband, who is muscular, but small statured (5' 8").  It fit very nicely (not tightly though). He normally wears a bit smaller than a small, but I decided to err on the side of caution and go for the small.  It's a bit looser than the picture.  If you want a tighter fit, go for the smaller size, but if you're looking for a normal workout shirt go for the normal size.