When I hear people say, "Oh I really should get back to the gym," it's usually in the context of, "I need to lose weight," and I think that's generally true in our society (especially, though not exclusively, for women). One of my coworkers does talk about how she's so much happier when she's going to the gym regularly -- that she just feels better when she has a regular routine of physical activity -- but mostly the conversations stay on the superficial level of "I need to lose weight." (And let's not even talk about how we're "bad" when we don't go to the gym or we eat high-calorie sweets or whatever -- how our choices about things like food consumption get framed as ethical choices*, in both advertising and society ... la la la Jean Kilbourne or whomever.)
*It occurred to me after I wrote that that our consumption choices are ethical choices in a lot of ways -- did your food have to get trucked in from halfway around the world, thereby adding to carbon emissions? were the workers who helped produced this item compensated fairly? etc. -- but I mean the ways in which we talk about food as being "sinfully good," for example, wherein food and sex and pleasure get all entangled in this dysfunctional thing we blame on our Puritan heritage.
I was always boggled when coworkers whom I knew went to the gym wanted to take the elevator ("I go to the gym so I don't have to take the elevator"). I want to be able to hoof it up the four flights of stairs from entry level to my office and beat someone who's taking the elevator and not be out of breath. Yeah I'd like to have tighter abs as a purely aesthetic thing, but I am going to the gym because I want my legs and arms and cardiovascular system to be stronger and healthier. It is so much more satisfying to push up the numbers on the speed and incline on the treadmill or on the weights in the strength training room (machines and free weights) than it is to push down the numbers on the scale (and yes, I admit that I've gotten sucked into weighing myself at the gym on average once a week [not that I tell anyone the numbers, but the scale is right there, and numbers are seductive] and I when I hit the upper end of what I think of as my regular range, I get nervous and start paying more attention to my junk food consumption for the next few days**).
**General note on food: I think consuming lots of processed food probably isn't the happiest thing for my body, and I'm trying to train myself to be attentive to what it is that I really want to eat rather than just eating whatever happens to be convenient (and also having more healthy stuff be what is convenient -- fruit, yogurt, Fig Newtons, whatever, instead of Hershey's Kisses or Peanut M&M's), but I'm not gonna feel guilty for downing a whole package of Ferrero Rocher from time to time.
I grew up walking everywhere and stubbornly walk the 1.3+ miles between Davis T and my house (and the 0.5+ miles between Harvard T and my work) and frequently stand when on the subway if I'm only going a few stops. I loved having someone recently comment on my arm muscles, since I've always thought of myself as having very little upper body strength. I was surprised and pleased when Prof.MikeW. commented on my good posture one day (and FUH agreed with him when I mentioned it to him today -- we were discussing replacing his broken desk chair) because I have slight scoliosis and was never motivated to really do the back exercises when I was younger (nor do I do them now). I love that I can do a less-than-fourteen-minute-mile for over three miles on the treadmill -- with an incline, to boot. I find it kind of amusing that I'll be not even conscious of how fast I'm walking and people who are with me will ask me to slow down.
Strong bodies are awesome.
Addendum: Sweet Machine at Shapely Prose quotes Jane from Casual Blasphemies as saying (re: common mentalities around dieting), "Self-loathing is not a fucking character-builder. It doesn’t make you stronger. It doesn’t make you better. It’s just an ever-deepening, creepy-ass trap; a trap that is a huge moneymaker for corporations that do not have and never will have good intentions. You’re not disgusting. You’re not freakish. You’re not ugly. And you’re never going to be perfect. And holy shit, that is so okay."