eh? I aim for 90% on 25's so thats an hour of "hell" 10's are more like 93% so 23 minutes of "hell".
eh? What you aim for on a 25 ( or any other TT for that matter ) is to be at certain points on the course within certain times so you know you will be on the podium.
Your heartrate will be what it will be. It doesn't matter a jot.