How long, realistically, would it take my 4 mile from from 45 min to sub 30 min?

What does the 30 minute run require? Physiologically, in order of importance:

  • Aerobic conditioning. Our oxygen-carrying system must be in top notch, from the lungs taking in oxygen, the heart pumping it into blood, and the working muscles picking up that blood and using it. This is simply the basis of performance for any distance runner.
  • Lactate Clearance. The ability of the muscles to clear waste products during activity. The more efficient our muscles are able to do this, the higher intensity we will be able to run at for 30 minutes.
  • Basic Speed. Which is the neuromuscular ability to run and maintain an efficient stride and leg turnover (we are not concerned about energy system demands here). While basic speed is not directly needed (because you can already run the 400m in 1:52), it is valuable to train for the following reasons: it improves your efficiency dramatically, making it easier to train and to race at given speeds. it reduces your risk of injury (making it easier to train consistently for a long period of time). and it takes very little effort and time to include basic speed training.

Aerobic Conditioning is improved by all distance running. Now, some people find this hard to believe, but your body does not know what a mile is. From a training stimulus perspective, it responds to duration and frequency.

Lactate Clearance is improved by running at an intensity that causes lactate buildup, stimulating muscles to clear waste products. We refer to this intensity as the lactate threshold. Truthfully, any intensity above the lactate threshold causes lactate clearance stimulus. But it is advantagous to us to run at the lowest intensity that causes lactate clearance stimulus, because we can run for a longer duration.

Basic Speed is trained by very short bursts of fast running, with very long recoveries so that the neuromuscular system is fully primed. Training the motor patterns of efficient running teach our body to run more efficiently at all intensities, and efficient running translates into both speed and lower risk of injury. But, we’re not going to head to the track and do specific speed workouts. Instead we are going to insert short repetitions called strides into some of our easy runs, so that we aren’t dedicating whole workouts to basic speed, and we also get the benefit of directly integrating these motor patterns into our easy running.

This nerd mumbo-jumbo aside, all training is about three things: frequencyduration, and intensity. Training creates a stimulus, the specifics of which are determined by the three key factors. You recover from the stimulus with adaptation. Our mission is to create the right stimulus for success at the task of the 30 minute run.

How do I get faster?

There are many factors that affect your speed, and you can spend many hours reading about this subject. The basic principles tend to be the same regardless of which specific distance you are training for. Things to consider include:

  • Base Building: Safely and steadily improving your mileage is often the first thing to consider. You can read more about this herehere ,here and here. Ensuring you have a solid foundation of plenty of miles should help you to avoid injury as you prepare for a race.
  • Quality: Once you are established in your running it is a good idea to incorporate some form of quality, whether that is hill sprints, intervals, or tempo runs. What sort of quality to include will depend on your goals. Read more here.
  • Lifestyle: Make sure you are getting a proper diet, are sufficiently hydrated, and get enough sleep. If you are under or overweight then addressing this may also help with your speed. Make sure that you are managing any medical conditions (e.g. asthma) appropriately and that you remain vigilant against any new injuries.
  • A good place to start would be this introduction by /u/HDRgument. It gives information on the main physiological factors affecting running performance, the training used to target those factors, and how to gradually build your training.

If you are ready to take your running to the next level and want to understand more about the principles behind training and getting faster, Daniels’ Running Formula is a good read.

How do I fix my form/footstrike?

The canonical bad running form looks something like this: slow cadence, long leaps, landing on a straight leg, ahead of your body, hands in front of your chest, upper body bent forward (slouching). What happens here is that the entire body weight, plus a good portion of the forward momentum you have, is jammed straight into the ground, and because the knee is straight and the hip muscles don’t engage properly, the impact force ends up hitting the bones and joints, all the way from the feet up into the hips and lower back, and even up the spine to the neck and head. Bones and joints are not built for this, so you will get in trouble with this. Now, typically this kind of running form combines with a pronounced heel strike; that’s because it is essentially a grotesquely scaled-out walking gait: you basically just lengthen your walking stride, add a bit of push-off to turn your steps into leaps, and that’s it. Forcing a forefoot strike will not change any of that; it might even make things worse, because one, you will be inclined to “reach out” with your toes, making the overstriding worse, and two, hitting the ground this way with the foot in an overextended position doesn’t help at all, it’ll just hurt the ankle joint more.

The proper solution is to forget about footstrike entirely, and instead work on a better overall gait. That means:

  • Short, quick, light steps, even (especially!) at slow paces.
  • “Run tall”: keep your head upright (imagine a string pulling your head up, like with a puppet), eyes on the horizon.
  • Relax, especially feet, ankles, arms, shoulders.
  • Bend the knees.
  • Keep your feet behind your body.
  • Use gravity to move forward: just slightly pushing the hips forward and down will have you effortlessly accelerate while staying completely relaxed. Practice this in the form of strides.
  • If in doubt, bend the knees more.

If you do all this right, you cannot possibly overstride, and rather than jamming impact forces into your knees and even losing a lot of energy by braking with every step, you will use your muscles and tendons to dynamically cushion the impact. It’s very likely that adjusting your form like this eventually leads to a forefoot strike, but if it doesn’t, don’t sweat it - as long as your steps are light and dynamic, it doesn’t matter at all.