As another poster said, it's probably a better measure of fast you'll recover than a predictor of how aerobically powerful you are. A better number might be your LTVO2 (or whatever it's called these days), that is when does lactate show up as a percentage of your VO2? Does it show up at 80% of your VO2 or 88%, etc. Very informative number for 10K and up, but I'd argue somewhat for 3K-5K as well (it's happening faster). But there are other tests you learn in a basic human anatomy/physiology or animal physiology or intro biochemistry class. Total lung volume, tidal reserve volume, glycolysis, Citric Acid Cycle, anaerobic, etc. My point is don't take the VO2 number (even if done in a sports physiology lab) as the ONLY measure of your aerobic/cardiovascular fitness, or even the one to base all your training around. There are multiple layers/factors involved as to how efficient you are or can become. But it's great you are looking into this. Buy or download a basic biochemistry text focusing on the cellular energy systems if you want more information. You'll realize there are thousands of reactions going on in a cell (regardless if muscle, heart, brain, liver, etc) every second. When you put them under stress (that is, you make them need more energy like during exercise) that number of reactions goes up or increase in rate, or some reactions change to handle the new stress, therefore generating new by-products (wastes, like sarcolactic acid!) that have to be dealt with, that lead to negative feedback mechanisms (you'll find your body wanting to slow down to recover, etc). It's not just a "VO2" or "Anaerobic Threshold" or "vVO2" or "Lactate" as the definitive training tool. Your body is utilizing multiple energy pathways all the time! But obviously during high level aerobic exercise (like racing a 5K) certain pathways are used more because they produce more Adenosine Tri-Phosphate, the basic energy molecule used in muscle contraction, than some of the sub or helper energy pathways.
As it relates to training? You have to experiment (or with a coach's help) around to figure out which workouts seem to help you improve safely, consistently, and sequentially (building towards a goal in the short term or long term). I did find the few years I coached, athletes responded better with better gains to slightly slower repetitions with slightly shortened interval recoveries. It seemed to help them adapt better. So if you've run 19:11 (so like 6:10-11pace), and were doing like a basic 5-6x800m workout you wouldn't do the 800's at like 2:57-3:00 with 3:00recovery. You'd do them at like 3:00-03 with 2:30recovery. By slowing them down a wee bit you don't go anaerobic too early (that is, quickly pushing your body into needing more anaerobic help than it should too early), but by shortening the recovery you sort of work the aerobic side more. I'm sure some message board masters will pick this apart, but I've just found it works...plus it kept athletes from being stale for races because they were doing their hard sessions within reason. My real advice to you to see consistent gains would be: learn how to recover properly from any workout you do, whether long run (more steps equals more biomechanical stress on feet, ankles, calcaneal tendon, up through knees to hips and back), 'tempo' run (you burn through a lot of calories and glycogen to do this so you need to replace that quickly as your body repairs itself), anaerobic session (recommend some protein within 30-60minutes after), etc. It's in the recovery between workouts that your body either adapts (becomes more fit) or begins the slow process of heading towards plateauing or breaking down.