Thanks for the feedback. I agree, riding at FTP for 6x5' should be doable.

I don't have power on my bikes, so the only power meter I have is in the Zwift world (their estimate/calibration of my CycleOps trainer). Which may or may not be a good comparison to the real world... but since I have no comparison, it's not a big issue here.

Zwift bases your FTP on rides in the system (it's also rider-adjustable). I did some rides on Zwift at the end of December, including a century ride. So it had good data to base it's FTP estimate.

The wild card, I donated blood on Jan 5, and I donated double red blood cells for the first time - the donation center said I'd be the perfect candidate and I didn't do any research until after donating. The days following the donation, I could barely stay awake at work. Then I started doing some search and I found many blogs like this . It's now been 7 weeks and I don't feel it in daily activities. But I do feel weak when riding, specifically holding my FTP. I can hold tempo all day without an issue. It's my theory that the reduced red blood count is hurting my strength when riding at FTP.

Another factor I didn't bring up in my first post: I do ride outdoors 2-3 days a week, so I'm riding more than the Zwift schedule. However, this week I took a rest day before the work out above - I knew this was going to be challenging workout. Still couldn't get through it, mostly because of weak legs not cardo.

Edit/afterthought - here's a link to the workout plan: http://whatsonzwift.com/workouts/10-...wk-ftp-builder