It already exists. You make it yourself. Unfortunately it seems to work best AFTER the unpleasant “getting in shape” phase. Getting in shape does suck (IMHO). Staying/Being in shape can be rather pleasant.
I wouldn’t mind a little button on the back of my hand to trigger it though 
No problem. Thanks for the straight dope. But pi is 3.15926, so how can you round it to 3.144?
I generally hate exercise because it seems boring and tedious and I resent giving up a precious chunk of my life for it. So I looked for ways to exercise that wouldn’t take any time out of my life. One that I found: stair climbing. I can easily go up forty flights of stairs during the course of my day. Just getting out of the subway is at least ten flights. Walking up the uncrowded stairs is quicker than standing on the crowded escalator. Then, at work, taking the stairs is nearly always quicker than waiting for the elevator. And when I want to be good and do some just-plain exercising, my high rise apartment building’s stairwells are perfect. There is no one to observe me huffing and puffing, I can go up until I’m tired and then take a break by going down a few flights, and fifteen minutes gets my heart rate up respectably. Oh and, one time, I experienced the “runner’s high” on the stairs. I had gone up until my legs would barely move to the next step, and were so wobbly they would barely support my weight, and then suddenly I jogged up ten more flights with no tiredness in my legs at all. Strange. If anyone is thinking of trying stair walking: be slow and careful going down, or take an elevator down. It’s easy for your legs to buckle.
Also, I’m a teacher, and during good weather I chase the kids around on the playground every day. That’s at least twenty minutes of cardio without taking time out of my life.
And I’m about to start a class in ballroom dancing, mainly in order to meet people, but I think it counts as exercise.
I guess I’m trying to say, it’s great if you enjoy exercise, but if you don’t, as long as the exercise is serving some purpose that’s meaningful to you, it’s okay. “Becoming fit” alone wasn’t motivational enough for me but saving time, bonding with my kids, and meeting new people (through exercise) ARE motivating.
Pi is 3.14159265… So you’re both off.
That’s really more like a Second Wind mentioned earlier. A runner’s high is more subtle and longer lasting than that, at least when I hear most people talk about it.
It does have a downside, as I experienced this weekend on my long run. I ran for just over 7 and turned to head back home. At that point I started feeling pretty good and the miles seemed to go by fairly effortlessly, even though I was going back up the Newton Hills. I decided to add a bit more to my run which I shouldn’t have, I was scheduled for a lighter day and at mile 15 I started feeling a little pain in my knee. I should have ignored the runner’s high and kept to my schedule.