Measures of Running Ability

The ability to race fast boils down to only a handful of factors. They are of course interrelated but here is your one shot guide to the performance measures as far as I understand them.

First there are genetic factors that you don't get to pick, because you can't pick your parents:

1. Fast-twitch muscle fiber percentage in the running muscles. From my limited understanding everyone has somewhere between 10% and 40% of their running muscles as fast-twitch muscle fibers. Where you stand on this scale basically indicates where you have the potential to race. I probably have 15-20% fast-twitch, I'm slow but not as slow as some. Usain Bolt probably has the maximum amount of fast-twitch fibers. Interestingly enough David Rushida probably also have the same amount of fast-twitch muscle fibers as Usain Bolt, but he was raised in a different culture thus an 800 running instead of 100 and 200. I'll discuss cultural difference later. Ideal training: hope that your parents are both doctors with personalities who set world records on the side.
2. Biomechanics or anatomy of your bones and joints. Basically some, perhaps most, people do not have body structures to handle the rigors of training. In this respect, I'm nearly perfect. By perfect I mean there are probably only a handful, perhaps a few thousand or tens of thousands, of people that have the angles that I do or better than I do and can handle the stress that I throw at my body. Although, I feel this aspect is largely influenced by your single digit years when your bones and muscles are still growing. I'll get to that later as well. Ideal training: same as above plus do everything active when you are young.

Second there are the primary trainable factors:

1. First is the percent of muscle fibers used. In an all out sprint away from a lion you will be using probably 100% of your muscle fibers because your body really wants to get away from the lion. When you go for a casual run over relatively flat ground you will be using roughly 30% of your muscle fibers. The more fibers that you use the less force each fiber will use to propel you at a given speed and the longer you will be able to maintain that pace. Ideal training: 8s-12s hill sprints, starts, lifting weights, 100m and 200m hard, and runs over 60 minutes in length (yes I mean long runs).
2. Next is anaerobic capacity, the amount of lactate you can handle in your body before you start jogging again. For the top guys this is 20-25mmol of lactate at the end of an 800m. This is well understood and trains in only a couple of months. There are many literature sources that describe training for this. Ideal training: 10x400m at mile or 1500m race pace with two minutes rest, basically any interval session with repetitions one minute to three minutes at a pace around 1500m to 3000m race pace.
3. Third is maximum oxygen uptake or VO2Max that is basically the maximum amount of oxygen that you can breathe in and out, typically 100% ranges between 5k pace for the top athletes and 3k for slower athletes, and it might even be the mile for untrained individuals. Again there is a plethora of training info out there about maximum oxygen uptake. Ideal workouts: interval sessions of two to five minutes repeats at 3k to 5k race pace.
4. Fourth is lactate threshold which ranges from 2mmol to 7mmol, typically averaged to 4mmol but it is the pace you can manage to run for 1 hour. It is kind of like the maximum aerobic pace. This is a steady state. If you run 1mmol faster than your lactate threshold in a one hour race you will hit the wall and your legs will get really healthy and you will have to slow down significantly. Ideal training: 20 minute tempos at lactate threshold pace.
5. Fifth is what I refer to as aerobic capacity. It is typically given as 2mmol and other times as marathon pace, but I feel it is realistically the pace you can handle for 3-3.5 hours. This is the magic bullet of distance running. Unlike all of the previous paces, which accumulate lactate and more or less have a time limit that you can handle that particular stress, aerobic capacity has no ceiling. When the top guys are trotting 4:40s pace in marathons it is because they have the ability to run 5:00 minute miles aerobically or using very little lactate. Ideal training: lactate threshold +3% to +25% for highly trained athletes and +3% to +35% for lesser trained athletes. That means for a person with a 6:00 minute per mile lactate threshold (moderately lesser trained) paces of 6:11 (+3%) to 7:48 (+30%) per mile will produce the most advantages, given that the training is over level ground with good traction, running up and down muddy hills will slow your pace considerably but keeps a high effort even at much slower paces.  
6. Next is efficiency and there are two types:
1. Aerobic efficiency is the ability of your muscles to use most of the oxygen being transported to them. Famous efficient runners are Alberto Salazar and Derek Clayton who had low VO2Max values and high efficiency. Ideal training: 8s-12s hill sprints and 200m sprints (increase your heart stroke volume so you pump more blood to your muscles) and more aerobic capacity pace running. Typically the guys that run the most have the highest efficiencies. Also, small calves (less mass on the pendulum) one of those factors you don't really control.
2. Metabolic efficiency is the ability to burn fats instead of carbohydrates, a critical factor in marathon success. If properly trained you will not hit the wall or slow dramatically in the later stages of a marathon. Ideal pace is lactate threshold pace +5% to +15%. Ideal training: 45 minutes to 90 minutes at lactate threshold pace +5% to +15%, either at a constant pace or progressing from +15% speed to +5% speed. Also, runs over two hours at slower paces help, but runs over two hours increase the risk of injury for most people. 

Third there are the scientifically undefined factors:

1. The ability to recover. This seems to be related primarily to two different factors:
1. What the kid or athlete does the first 10-15 years of his or her life. The more active a kid is at a young age the better the ability to recover throughout at least one's 20s. In other words, Ryan Hall grew up in Big Bear, a very active mountain town in California. He played every sport before finding running at age 15. My parents never bought me a game system, but they bought me a plethora of sporting equipment and now I'm as healthy as they come. I think that more and more kids these days have sedentary upbringings, thus we get injuries on our college team.
2. The volume of the work that the athlete has done in the recent past. The more that one does, the more one can do. If you start running and run five miles a day every day it will be hard for weeks or even months, but there will come a point after several months when five miles every day becomes easy. It will take at least several months, but eventually it will be easy.  In other words, when I am averaging 15+ miles a day I can do my hardest workouts and come back a few days later and do another hard one. A great quote I read a few weeks ago: "But if you're not tracking time or distance you can do almost anything." It is in reference to Lindgren running 40 miles a day as a teenager. 
2. Flexibility. Basically, if you grow up running and walking barefoot you
   if you grow up running and walking barefoot you have the best chance of having above average flexibility. Many of the east African professional runners have leg flexibility far greater than most Americans. I feel it is due to going shoeless for most of their first 10-15 years. My flexibility is terrible.
3. The mentality to pursue, whatever you are pursuing. The will to fail and fail again and again. Some people just don't have it (cough, cough, instant gratification Americans).

Getting back to cultural difference between Jamaica, Kenya, and the United States. David Rudisha has a 400m PR of 45.50s, Usain Bolt has a 400m PR of 45.28s, and here is a guy Robert Griffin, that I have never heard of but he plays football instead of running track even though he was a track athlete who ran 49s in the 400m hurdles and 46.9s in the open 400m in high school. In Jamaica Bolt chose running so that he could be the best in the world versus just another good soccer player. In Kenya Rudisha chose running, because it is the only sport in Kenya. In the US Griffin chose football because it is the only sport in the US, I mean it is a sport with lots of money, I mean it is the sport with the most fans. He did run at Baylor under Clyde Hart for a semester and ran in the semifinals at the Olympic Trials in 2008, as basically a high school senior. 

So there you have it