Discussion: You were right on..

Your last race, 13.1 miles in 1hour 31 minutes gives a Vdot of 50.3 and a T pace of 6:49.

I have a decreasing Vdot progression; it seems clear that I am mechanically better suited to short distances. I infer that I have a comparatively high proportion of fast twitch muscles.

Distance: Time, Vdot
1600m: 5:22, 54.5
3000m: 11:13, 51.7
half marathon: 1:31:25, 50

The last time I ran cruise intervals, I was using my mile pr, from February, as a benchmark for my pace. I didn't seem to have any problems running 4:45 1200s.

Whatever Vdot I should use, it's apparent that I need to get fast. Any suggestions, besides more quality like VO2 max intervals and threshold runs?

Don't be so selfless. Donate less blood, save fewer lives... I mean thanks for donating :) I run faster when it's light out. you might try that.

You really thought it was a good idea to do intervals the day after giving blood?

Isn't it something like 2-3 weeks before you can expect to perform after donating blood? I wouldn't read too much into your slower-than-expected times the day after giving blood. silly.

Good job giving blood, though.

I've found at least a week after donation is required before racing and speedwork or else I see the little tweetybirds circling my head like in an old cartoon. I could just have weak marrow.