I like this workout because it has both a speed and an endurance component while also training the athlete to run fast on tired legs. It can also be easily tailored to the type of racing an athlete is competing in short course or long and where he or she is in their build cycle.
Warm-up
Start with a few minutes of dynamic stretching or movement prep. I like to use eccentric calf raises, glute bridges or clamshells, and standing, one-leg hip extensions.
Afterwards, run four laps of a standard track (roughly 1 mile).
Do the first two laps easy, then on laps three and four, run the turns easy and on the straightaways, do running drills for the first half (high knees or butt kickers) and then accelerate to 5K speed for the second half.
Main Set
12×200 fast followed by 400 steady
The 200s should be run quickly but not at an all-out sprint pace. The 400s should be run at a steady endurance pace.
If you’re just getting back into speedwork, you can start by breaking up the 12 200s into 3x[4×200/400] with 2 minutes rest between sets. Then advance to a 2x[6×200/400], and then to the full 12.
For short course athletes, run the 200s faster (around pace for a 400m repeat) and the 400s around marathon pace; for long course athletes, run the 200s a little slower (around pace for 800m repeat) and the 400s close to 1/2 marathon pace.
Total of 4.5 miles
Cool-down
Run a mile easy in the opposite direction around the track as what you ran the repeats.