T4 – This zone is all about race specificity and developing strength at that pace / power / heart rate over a period of time. Holding all intervals at the prescribed zone is the outcome I’ll be looking for is a full set at that level.
T5 – As a general rule if I prescribe T5 I will be looking for a top end level. It will have a long period of rest assigned to it also so you can have a good go at the intervals. At a minimum it will be 1:1 work:rest. When doing these have a real go and see if you can better your power / pace for that distance or length of interval. If you are doing a bike set on a smart trainer then switch “erg” off and rip in. I’d prefer you to see if you can set a new level and experience failure in the other reps than protect yourself and hold all reps at an even level.