In the story, Slamm-0! is fitter. that, or Netcat has a thing for doughy dudes. Don't laugh, it happens.

Anyway, this was brought up on Dumpshock, and I'll paraphrase some of the replies from there...
1) It's never stated exactly when Netcat took those pictures. I believe the "pictures" in question may have turned up on JackPoint in '70, or maybe '71. But they could have been taken a few years earlier.
2) A lot's happened since then. Many of us know from first hand experience, it doesn't take long for a body to fall apart if it's not that active. And Slamm-0!'s gota kid to watch now. I imagine he takes a lot more "overwatch" jobs on the Matrix rather than physically going in with the team, and he's probably taking advantage of being a "Stay At Home Dad" to watch baseball and play video games.
3) My personal excuse? Netcat's maternal instincts kicked in, and she likes to bake cookies. And muffins. And brownies. And Cake. And Slamm-0! loves to eat them.

Slamm-0! was fit and beefy... 3+ years ago. Now? He's a couch-potato

Bull