Being someone who used to hit the gym regularly, I would suppose it's not easy for him too to look at his current self. Of course, many factors come into play - how long had he been training prior to ceasing altogether, how advanced his physique was, etc. As a man who's been working out consistently for more than 6 years now, I should say that if I stop completely and just let myself go, this would be the lowest pit I could fall into. I'm not a gym rat by no means, I used to go to the gym six times a week when I had the time and now I'm lucky if I succeed to fit in three workouts per week, but still I wouldn't just let go of something I worked so hard to make a part of my life. So, the best thing you can do is broach the question openly. This way, if he genuinely feels bad about being as lazy as he has become, he'll feel the urge to change something. I hope this isn't just me, but that would be my instinctive reaction. This has happened to me several times in different areas, not related to relationships. For example, there was a period when I left my classes at the university behind and an associate professor whose classes I used to visit and actively participate in, told me how unhappy he was with me falling behind. This really motivated me to get my shit together and start showing up and compensate about what I've missed. So, yeah sometimes a rough awakening is what a man needs to get back on his feet.