Is it possible to improve or maintain your speed at any distance by doing the following: Hard workouts 1-3 times every two weeks where 75% or more are races and the rest are race pace workouts. Easy workouts 3-5 times a week. Over a months average 12 runs, so its likely to be low mileage but many high intensity runs due to the races.
What you are essentially describing is a typical high school cross country season. Our typical in season weeks consisted of the following:
- Sunday - Off or easy short run
- Monday - Shorter run, fartlek/indian run type setup.
- Tuesday - Longer run, in the 6-9 mile range, easy pace.
- Wednesday - Speedwork/hill work
- Thursday - Longer run, easy pace
- Friday - Short run/off
- Saturday - Race
We were anywhere in the range of 50-75 mile weeks, and in college, that was bumped up to 75-100 mile weeks depending on where we were in the season.
One thing that has been critical over the years is base. Base is the king of all, if you have a solid base behind you then it is fairly easy to maintain on a lower amount of running. So yes, if you have a good base, I would think that it would be fairly easy for you to maintain your current level on a limited amount of running. If you want to improve, you may need to up your daily mileage. As a coach I know says, "Just run. Run lots. Mostly slow, sometimes fast." The biggest thing I've seen with runners is they simply go too hard all the time.
In short- Yes. But...
12 workouts on average is not such a small number, but as I perceive from your question, that they are scattered around and not very planned2.
I think doing scheduled workouts is the best option to go. You know when you're going to train and can eat and rest accordingly. There are many training plans and things you can do to advance in little steps instead of trying to go up a lot each time with hard workouts.
Usually when I train for the sake of training, I increase the length of my run, and when I'm training for a race I set myself a static amount of kilometers which each workout I must complete in shorter time.
So, you can get better at running, but you're not maxing your full potential in those trainings.
Something that left a huge impression on me.
Years ago when I was finishing up grad school -- I worked as a personal trainer. I would rent a gym hourly from a (friend of a friend). The guy had an entire wall full of trophies and metals. He told me he's a ultra marathon runner (50 - 100 mile runs) he was #2 in the world at the time...
Anyway long story short he always lifted 3 / week ran the other 3 with 2 being a mix of interval type of work. He only ran the distance of his races once per week. He was ripped and didn't have the haven't ate in 2 weeks look.
Bottom Line -- All of his work involved increasing INTENSITY NOT DURATION (yes these workouts will save you time and give you faster results)
One of the best books I've read to date "Core Performance" it has some great sample plans of how to setup and progress your workouts.
Energy System Development (ESD) is the cardiovascular component of your training program. Your body has different energy systems and ESD trains them all.