As I'm also competing in middle distance races on amateur level, I'd like to give you some insights into this wonderful sport.
First of all, there are three things you need, when you want to run the middle distances (800m / 1500m / one mile), I will concentrate on the 800 metres, because it's "my" distance.
1. Basic speed (anaerobic conditioning)
This is especially important in 800m races, because without having decent sprinting abilities you just don't stand a chance in tactical races. The pros usually are able to run the 400m in about 46 to 47 seconds (Rudisha's personal best is 45,50!), and they're easily able to run 100m under eleven seconds. You also need the basic speed to wear down your opponents in fast races.
2. Aerobic endurance
You can't run 800 metres fast, when you're solely concentrating on your sprinting abilities. You also need to build up a fair amount of stamina, because otherwise the human body isn't able to stay under the lactate threshold long enough. (the LT isn't the only limiting factor here, and it's also not a "wall" you hit, it's more like a transition from "this hurts" into "fuck my life, I want to die")
3. The will to suffer
Rudisha needs 101 seconds to run 800m, which means that he's running 100m in an average speed of 12,6 seconds. This is faster than most people are able to sprint this distance. Now imagine that you have to run eight times the distance. Running the 800m means pain. Exercising means pain. Even winning means pain sometimes.
The 800 metres are a very special distance, because aerobic and anaerobic factors are EQUALLY important.
There are two basic types of 800m runners:
1. The 400 / 800 type
- good sprint
- able to run at a fast pace constantly
- offers weaknesses in races, where the pace is changed a lot
2. The 800 / 1500 type
- good stamina
- able to run at a decent speed constantly
- isn't the best sprinter, but can react better to little attacks
Rudisha is more like a type 1 runner, a good example for a fast type two guy is the british legend Sebastian Coe, who ran the 1500 m in 3:29.77, which is still an amazing time. Please note that these types are models to show you some basic differences in approaching the middle distances.
My personal experiences:
I used to run a lot in my teenage years, and I've started to train again one year ago. I know that I'll never be able to compete on top level, but I have a dream: Beating the two minute mark. Compared to the best runners in my country, who can run faster than 1:50 with ease, two minutes are slow. But running the 800m in two minutes still means a 100m average of 15 seconds, which isn't slow at all. (at least for me )
I've gained some weight during my inactive years, so my first goal was to lose some pounds and get back into decent shape. Now I'm close to my initial goal (70 kg / 180 cm), and I'm concentrating on building up my sprint abilities again.
My training consists of long runs (up to 5km), "fartleks" (longer runs, where the pace is changed a lot), interval training, sprint training, some minor lifting and fun stuff like playing football (soccer for you americans...) and swimming.
Now the sprinting part and the grueling intervals are taking up most of my time, I will compete in a test race in september (goal: 2:20). I'm also part of my university running squad, which makes training much easier.
My personal best times are:
1500m 4:35 (I hate this distance...)
Currently, I'm nowhere near that times, especially my sprint is terribly bad. As I'm 27, I know that I won't become faster with my increasing age, but I think that beating my old PB is still possible. Going under two minutes is more like a dream, I know that it's likely that I won't reach that level, but without a dream, training becomes boring.
I hope I could give you some interesting insights. Keep running!