I'm a hobby jogger. Nothing wrong with that except that I own lots of books and have spent way too much time thinking about how to run faster when the answer is simple to comprehend, but difficult to achieve: lose weight.
At 5'9.5'' and 163 lbs, I'm not that heavy by 2010 standards, but I could be much lighter and still healthy. As a freshman in college, I weighed 138 lbs at this height and when I took a fitness class that included a skinfold test, my body fat was 11%. I met Alan Webb once and we're just about the same height (I'm maybe 0.5'' taller) and I have a smaller frame, but he weighs 20 lbs less than me and could bench my weight 40 times while I can't do more than one pullup.
Pace is roughly linear with weight for small weight changes, so if you drop 1 or 2%, you can expect to run 1 or 2% faster. If you drop 10%, it might only be 7%, but you get the idea: there is very little you can do to improve your race times that's more effective than losing unneeded weight. Notice I said "unneeded weight." I'm talking about the ridiculousness of a middle-aged guy with a gut wondering why his lung-searing 10x800m interval sessions aren't propelling him to distance running greatness.
Of course you have to run also. When I weighed 138, I think I ran 1.5 miles during our Cooper test (12 minutes) at the beginning of that fitness class. Now, I would probably cover 2 miles in that test (according to McMillan my 32:07 8k is conveniently worth 12:00.2 for 2 miles). Of course, I ran that 1.5 miles while being utterly sedentary. When I started running at 33 years old and 187 pounds, I might have covered 1.2 miles in 12 minutes on a good day.
OK, so unless your already close to your ideal weight, the answer is to run as much as your schedule and body can tolerate and to lose weight. The first helps with the second, by the way. I had a coach last year and I really started to slow down after April when my mileage came down as we shifted focus to higher-quality, lower-quantity 10k training. Not coincidentally, my weight went up as well. I don't think it's easy for good runners to comprehend the tubby tendencies of the hobby jogger. We like to eat! I have a friend who's a very good runner who at over 6' weighs 150 lbs when at peak training and "ballooned" to 155 when a knee injury sidelined him completely for months. I think a lot of "talent" has to do with being skinny. Sure, the "talented" probably eat better on average, but they don't necessarily struggle with it. (I also know a former D1 runner who no longer runs and eats like you wouldn't believe, but is as thin as a rail.)
So, how to train? I could of course save a hell of a lot of time by just shoving less food in my mouth, but as millions of people already know, that's damn hard! Running 10 times a week seems easy by comparison. ( I'm hoping one day I can get both to happen at the same time.)
I think burning as many calories as you can is a good place to start. This means running lots of miles and not getting injured. How?
- Doubling when you can is a good way to burn extra calories without much injury risk. (Cross-training would probably work, but I can't seem to fit that in my schedule while lacing up shoes and going out the door is pretty easy. ) As an added bonus, I don't snack between arriving at home and eating dinner if I'm running and showering.
- Limiting off days. The effect of your heroic workout or long run will be negated if you add ounces the next day by eating and not running. Don't waste a perfectly good day.
- Up the average intensity if you've hit the limit of your time budget, but try to do it in a way that doesn't reduce the calories you're burning by "wasting" days recovering. Right now, for me, this means moderate running (HR in the 150s) every third day or so.