Here's the thing. You take 90 seconds jog, and it's slow, both the heart rate and lactate levels will drop during each recovery. A good workout but not a good race simulation. You take a 50 second 200 after each race pace 1000 and after about two, heart rate and lactate stay level throughout the workout. It's mentally easier because of the slower pace but it's the closest you will get in a workout to the physiology of the race. If you really want to do 2ks with 90 seconds rest, do 4 and get in 400 meters during that 90 second rest. I actually use 5x1600 with a 400 in 1:40-1:45 for 32-34 minute 10k runners. 5x1600 with 90 second 400 for 30-31 minute 10k runners. One example of how well this predicts is a runner who went 5x1600 at just under 5 with 90 second 400 jog rest and then hit 30:53 in a race. On the other hand, I've had runners hit 5x1600 in 5 flat with 60 seconds rest - not fast jog - and they can't break 33 for 10k.