If you think you absolutely have no reason to exercise, I can give you one. Even if you're not overweight, even if you have tons of energy every day, even if your blood pressure is so low your doctor has to dig a hole to chart it, there's still one good reason to exercise.
Endorphins are a feel-good chemical your body distributes in response to stress or pain. Think of them as like morphine, only instead of your doctor injecting from the outside, your body is producing it from the inside. Any time you have a painful experience, or a stressful one, your body reacts by producing endorphins.
The endorphin reaction is two fold. First, a rush of endorphins are produced to deal with the initial pain. If you are suddenly placed into a stressful situation or experience a sudden pain, your body produces endorphins to try to deal with that situation.
Second, after the experience is over, your body starts to hold itself at a higher endorphin level, because it knows such an event might happen again. In other words, we come away feeling better and having a higher threshold for pain.
Just about anything you're passionate about or enjoy doing can probably be linked to endorphins. If you like roller coasters, it is largely because you enjoy that rush of good feelings you get from having been through that traumatic experience. What we've always called an "adrenaline rush" is actually more of an "endorphin rush."
Sci-Fi author Dave Wolverton has made a good case that the same thing happens when we watch a sporting event or read a book or watch a movie. Our body reacts as if we were involved in the situation (which, in a way, we are) and produces endorphins to react to the stress.
Whatever way we first discovered we could get this "rush," is the way we'll probably keep coming back to. People who read books or watch sports or do competitive activities are all looking for the same thing--a certain degree of stress, and the endorphin rush that comes with it. Even people who are addicted to gambling, in the end, aren't really in it for money. If they were, they'd have given up when they didn't get any. They crave that feeling they get when there's the possibility of all that money against the risk of losing it all.
Exercise is a way to do that every day. You put your body through enough stress to start producing those endorphins. It's not meant to wipe you out to the point you can't function--you just exercise to the point where you know your body's worked a bit harder than its accustomed to.
Then, endorphins kick in to deal with the stress. You feel better about yourself and about life. Problems seem easier to face and goals seem more achievable.
And even after the initial "rush" wears off, you're left with a higher baseline for pain and stress than you had before. Something that would have been a big deal before you started seems easier to handle after a few months of consistent training.
It's obviously not the only way to produce endorphins. There are ways like the ones I've suggested above. I also heard from Dr. Benjamin Martinez, a behavioral expert, that smiling produces endorphins, and that studies have shown that it works just as well even if the smile isn't sincere. In other words, smiling alone can sometimes help you feel better.
So go ahead. Become an endorphin pusher.