You can not tell by looking either. They were always scruffy and I swear they stick out their gut on purpose, just so you do not realize how fit they are.
My platoon leader in the Corps had been a SEAL in Vietnam. He changed services after that. He never talked about it. He had that massive chest on a normal sized body that serious swimmers seem to get.
He led us on PT for a while. He’d have us do a series of exercises that weren’t particularly punishing when we were doing them, but our bodies turned to jell-o afterwards. Every muscle we had was burning and stressed after PT with him.
The only thing that he had us do that was really demanding while we were doing it was to buddy up and carry your buddy in a fireman’s carry on a PT run. We didn’t run far like that- we’d switch off and you got to ‘rest’ while you were being carried.
I was on the DC metro one day and I was standing next to an older guy who was wearing a Team Six ball cap. He was tall, lean and muscular but he looked kind of odd. He just stood like a statue the whole 20 minute ride into DC. Didn’t say a word, just stared straight ahead. Kind of creepy.
My husband was with the Special Boat Units during his Navy service (1991-2000). He drove the boats for the SEALS and his back and knees paid the price for it. We knew several guys in the SBUs who had messed up body parts and worn out cartilage. I also babysat the kids of a SEAL for a while before our first child was born. Those guys are really that fit.
If my husband was lying about his service, then my time in Coronado, Roosey Roads, and at Stennis were figments of my imagination ;)