I had an emergency one (blood infusion) before my operation. I can’t remember it being too onerous though. I can’t say long term how it lasted as my op/own system kicked in after a week. Lol, I did have one TT in between and managed a 24:39 for the 10miles without going into z5 hr. Doped up on iron. I have managed 23.10 on that same course earlier this year though 
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