My worry is that the way I did it felt to easy for what is supposed to be the hard workout for the week:
I did this workout as part of some 1 mile training plan that I found online. My goal is to break 5:00 min. for the mile, and I ran these reps at 37s per 200m +/- 1.5s. This didn't feel tremendously difficult. Reps 17, 18, 19 were the slowest, and it was starting to feel more difficult, but know I was on the last rep, #20 was 34s. This represents the main Tuesday workout for the week, and there is also a tempo on Thursday, and a longer steady run on Saturday in addition to easy miles other days.
I never followed any running training plan until the past year. Until now, I just ran/jogged a couple 5k's per year with 3-5 mile runs/jogs 3-4 days per week year round, plus pick-up sports and adult rec. leagues (basketball, lacrosse, soccer, ultimate frisbee).