Originally Posted by
acedrake
*begin personal opinions
Speed is a lot less about pure force production - slamming your foot into the ground - and a lot more about technique and mental ability. This gets less and less true over shorter distances, but for 1.5 miles your limiting factor is probably going to be your brain's capacity to continue putting one foot in front of the other and the coordination with which you do it. You can't really train that on a periodization basis, it's just something you develop over time as a skill. The best way to train it is to go running regularly and get better at making your body go fast. Get up to about 15-20 miles per week (run 3 miles for three days, rest, run 3 miles for the next three days) for two or three weeks before your test and you'll have a good base.
What you'll want to do is work on pacing and race technique. Once a week, go to a 400m (1/4 mile) track for one of your workouts. Look at what you want your goal pace to be - say, an 8:00 min mile - and figure out what 1/4 of that is (2:00 for our 8 min example). Warm up, then time yourself running a lap at a steady pace. Get as close to 2:00 without going over. This is going to teach you what running that pace feels like, and how to hold it together while running that fast. Rest for 60 seconds, then do it three more times (this exercise is called repeats). Record each time and try to make sure that you're keeping the same pace - as close to 2:00 as you can get but not slowing down. Cool down by jogging a lap or so and head home. One speed or pace workout per week is the minimum effective dosage - any more than that and you'll blow out your knees at this point. There's plenty of internet resources on speed training if you really want to go overboard about this.
My recommendation is not to overthink this. An 11:40 1.5 mile is about a 8:45 pace - not that bad. I don't know what your requirements are, but you shouldn't need to take that big a layoff from training in order to see some improvements. Same with your weight, there's plenty of big guys out there who are awfully fast (before my eating dysfunction days I used to be one of them) and if you can move 500 lbs in any direction you've already got all the tools you need. Lay off the nacho bar maybe, but just make sure to eat your greens and your body will adjust. Being skinny doesn't make you fast, being good at running makes you fast.