HOW FAST SHOULD I GO ON THE INTERVALS?
You should go at a pace that enables you to maintain technique and speed across the intervals. If you are unable to hold your form or your speed starts to fall off then you have found your max.
There is a place and a time to practice mental fortitude in race practice or competition settings but training is a time to ingrain good motor patterning under increasing doses of stress.
The best indicator we have found to see if we are able to do the next interval is not necessarily overall time or distance, but the cadence at which you can keep. If your cadence is starting to diminish this is a great sign that your nervous system is starting to fail (per se). If you don’t know if your form is starting to fault or your cadence is slowing this is more of a question of understanding skill. Which more than likely points to you spending more time developing this area.
Depending on your experience level and distance or time of the interval you can be a little more generous about your deviations.