The reason, he said in a recent interview, was because he'd been eating badly in an attempt to soothe the stomach problems caused by his addiction to painkillers.
"When I got out of rehab, I needed to lose weight, but I also needed to figure out a way to function sober. Unless I was blitzed out of my mind, I had trouble sleeping. So I started running," he told Men's Journal. "It gave me a natural endorphin high, but it also helped me sleep, so it was perfect. It's easy to understand how people replace addiction with exercise."
In no time, Eminem, 42, was running seventeen miles a day on treadmill -- half before work, and half after. The rapper, whose real name is Marshall Mathers, became obsessive about burning 2,000 calories every day and dropped to about 149 pounds. However, he also hurt his hip flexors, and realized he needed to mix things up a bit.
"I tried out some of those workout DVDs you do at home. One of the first ones was Shaun T's Insanity workout. I know a lot of these DVD guys are wacky, but I'm alone in my gym; I need someone on the TV yelling to motivate me," he said. "Besides, some of this s*** is entertaining."
Mathers began mixing in other workout DVDs too, including the P90X, which he still uses for abs, and the Body Beast, which he does every day instead of running. Now, before he heads to the studio, he does the DVD workout with free weights, a bench and a pull-up bar.
"I guess I'm pretty compulsive working out. I feel like if I step away from it for too long, if I have a crazy week and take a five-day break, it'll be like starting over," he said. "I'm afraid that if it goes beyond that, I might lose the motivation. Once you're at a place where you've made progress and you've got some time invested in it, you don't wanna quit and give up what you started."