How does one improve leg speed (400 time) within the context of 1500/mile training? You can't just go out and follow a Clyde Hart-type schedule. You need to keep your mileage up, put in the long runs, doubles, VO2 max intervals, etc.
How does one improve their leg speed within that training framework? Ultimately leg speed will be the limiting factor. Can it be improved?
Running, and training is specific.
You won't become a faster sprinter, without sprinting.
Take one month of the summer and 3 times a week run 20 x 100 meters hard, fast, nearly all out, jog/run 100 meter recovery.
The second month of the summer, 3 times a week run 20 x 200, with 200 meter jog recovery, the same way, same effort, only runn the 200's at 80 percent. Add into that two days a week, run 5 x 100 meters, all out, full recovery.
The third month of the summer, 3 times a week run 10 x 400 meters at 80%, with 400 meter jog recovery.
Last two weeks of summer, run 6-800 meters at race pace, 400 meter recovery.
Do this while doing your base work.
It is tough to do, but you will improve fast.
And, eat well, get lots of sleep, stay well hydrated, no soda, reduce sugar intake, lots of green leafy raw veggies.
Why not follow a Clyde Hart type schedule? 35 yard flys are good. Drills. Block work. All that stuff helps.
Don't hurt yourself though.
Race a lot, and always sprint flat out at the end.
In training you need to do 400m pace and 800m pace sessions as well as 1500 pace 3000m pace 5000m pace for endurance.
The sprint at the end of a 1500m race is not usually flat out, look at the splits of the top runners, it is a long drawn out fast finish, often fading slightly in the last 50 meters. It's a combination of your natural speed, and speed endurance. You can never have too much speed endurance, so training at all those paces plus good mileage (whatever suits you best) is essential for a 1500/mile runner.
I think the 20x200 at 80% is maybe excessive. Especially during summer.
During regular base-training, and mid-season, I try to get in 10-12 100m or so hard strides (or 50m hills) - 3 days a week. That and lifting have improved my 400m, top end, and ability to accelerate. 400m has gone down from 57.x to 51.x in a few years (maybe faster - it's not like I run it often). I don't ever do 400m pace in workouts.