Exercise is statistically correlated with better health, but weight is not. That suggests you should exercise more. Furthermore some exercise is much better than no exercise at all, so you can be happy with a modest achievement.
Why don’t we rely more on markets to force ourselves to exercise?
Post a bond with your friend, your spouse, your exercise partner, or someone you won’t (or can’t) lie to. You lose the money if you don’t exercise according to a pre-arranged plan with well-defined quantitative goals. If need be, I will serve in this role and cash your check when it comes in the mail (hey, would you lie to your blogger?).
Or why not have the gym collect a bigger upfront fee, and they pay you each time you show up and complete an exercise program under their supervision?
What are the problems with these arrangements?
1. The roles of friend or spouse do not mix with that of "Enforcer." That being said, I bet your spouse is willing to enforce her requirements on you. And surely she wants you to live longer, so why not extend the scope of her enforcement just a wee bit?
2. The payment, if you lose, is not a real transfer. You share funds with your spouse and your friend will treat is as a gift to be returned. Fair enough, but then find a real bastard, a corporation, or an amiable but distant blogger.
3. You enjoy exercise, but not if you feel obliged to do it. Introducing too many external incentives takes away the possibility of developing internal motivation. (Similarly, if you pay your kid to do the dishes, she will no longer feel obliged and the total quantity of labor may fall.) If the exercise arena becomes a regular sphere of money loss and humiliation, you will avoid the exercise idea altogether. After a while you will stop making these contracts.
4. You don’t really want to exercise more in the first place.
I put most of my money on #3.
We hear all this superficial blather about "life being a process." This is true, but it is less well-recognized that this is a source of institutional failure. Most good things you do — and I include charity on this list — you do not for the ends themselves, but because you have somehow managed to enjoy the process of regular engagement and self-discipline. You then deceive yourself into thinking you value the end more than you do. This creates social order, but it also makes those same commitments fragile. Whether you are meta-rational or not, you are unlikely to seek brutal market discipline (or advice columnists, for that matter) to enforce your good behavior. You prefer to play the happy fool, even though you will die earlier and refuse to break up with the creep you are currently dating, no matter how many of your friends tell you he is ultimately a loser.
The alternative methods?: Fantasize about the relationship between exercise and more and better sex, whether or not it is there at the margins you face. Build fantasy upon fantasy to make the area a source of fun. Or try self-prophecy.
Addendum: Economist Art DeVany has intricate theories about exercise, based on his understanding of evolutionary biology. Run sprints, not marathons. Art reports on his blog how devastated he is from the recent death of his wife; do read this moving tale.