Oh man, interval training. I write of it with fondness. Also, with soreness. My treadmill runs used to look something like this:
30 minutes at 6 miles per hour
...and that's it.
I used to get bored SO easily, and my 30-minute runs felt like they lasted hours. All I could think about was how the sweat was running into my eyes, and how my lungs felt like they were exploding, and how my legs felt like they were giving out.
You know that three-headed dog in the Harry Potter series? Fluffy? Fluffy is terrifying. Come on, admit it... but what is it about him that makes so many children wet their beds? Why does even The Boy Who Lived turn and run like a little girl? I'll tell you why: it's because he has THREE HEADS. When one of them is trying to kill you from the front, you have to worry about the other two attacking you from the sides. I mean, jeez. Even if you cut off ONE of his heads, you'd still have a serious problem to worry about. Here's where I'm going with this - your fitness should be three-headed. Three-pronged. A Trifecta of Fitness. A tricycle of health and happiness that you can ride daily. Okay, okay, I'll stop.