[dkarl]

Okay, so first, I'm certainly not saying every sedentary person should hop up and run for an hour tomorrow. I'm saying you can get there in a month or two of reasonable effort.

I'm not an expert, but I read what they say. This is way, way out of line with what any experienced running trainer would tell a beginner. Not even a beginner who was, say, an extremely fit swimmer. Definitely not a sedentary beginner. You have to give your connective tissue time to adapt to the peculiar stresses of running. (Plus, beginners are going to have crappy form and inflict more punishment on themselves than necessary.) By the numbers most people use, it would be very aggressive, but possibly reasonable for some people, to ramp up to 42 miles per week in one month from a base of ~29 miles per week or in two months from a base of ~20 miles per week. And that's pretty aggressive. Trying to get to 42 miles per week in two months from a sedentary state would leave basically everybody injured except genetic freaks or people with a previous adaptation to high-mileage running.

If you're starting from a sedentary state with no weight problem or existing injuries, you might start with eight miles per week and ramp up to 42 miles per week over nine months. That's a 10% increase in mileage every other week, and it assumes you don't screw up and get hurt, which many beginners do.

And, if you'd prefer, get on a bike for an hour instead. It's lower impact, and you'll burn at least as many calories as running.

That might be more reasonable (if you can find someplace nearby where you can ride in a fast, sustained way without blowing through stoplights or terrorizing pedestrians.) I don't have personal experience with ramping up bike training (I just ride to work once in a while) but from what I hear it doesn't require as much care as running.

[xiaoma]

Nearly every high school cross-country runner goes from zero to five days a week of running instantly. I built up to over 62 miles and six days of training a week in the first season and I know plenty of others who have done the same. Not only that, but I did the same thing again 15 years later and 60 pounds heavier.

The human body really is designed to run. Most injuries are due to pushing to go too fast. If you keep your heart rate at about 60-70% of max, you'd be surprised how quickly you can ramp up mileage without hurting yourself. The key is to never push yourself so hard that you feel like you couldn't do a workout the next day.

Cycling works almost as well from a cardio-vascular standpoint, too. It's not weight-bearing, though, so it won't help improve your bone density or strengthen your joints like running will. You could probably compensate by doing a bit of weight training. In the end, it comes down to getting off your butt and moving.