8B) FARTLEK: Jog for 20 minutes, evenly mixing in 12 half-to-two-minute hard runs throughout. Run duration is your call, but push yourself.
8C) SPEED: Run for ten seconds, then jog for 90. 13 sets of 68 reps (add one set and rep each cycle).
INTENSIVE
8D) 15/15/15: Jog for 15 seconds, run for 15, then sprint for 15.
4 reps; add 2 each week.
8E) HILL/STAIRS: Run 100 yards up a moderately sloped hill, or run up some stairs for 15 seconds. Walk down. Hill: 68 reps; stairs: 10.