Workout:
12 x 400m
4 @ Threshold pace; 1 min. recovery
4 @ 5k pace; 2 min. recovery
4 @ Interval pace (about 4 sec. faster than 5k pace per 400m); 2:30/3 min. recovery
Another option can be:
6 x 400 @ 5k pace
6 @ Interval pace
same recovery as above
