Alternating 200’s and 400’s.
200m hard/ 200m recovery; 400m 5k pace or a few sec. faster; 400m recovery and so on.
Take a 2-3 min. jog after 4.
so, 2 x 4x (200m / 200m recovery; 400m / 400m recovery)
Pretend this 200m hard and 400m hard are hills, so work it.
5k pace or faster.