I have used TriDot for 3 years and it is a brilliant system. Based on your personal timetrials for 5km run, 20mins bike and 400m swim it calculates your range of paces. You input the events that you are training for and it calibrates a training plan tailored for those events - short or long distance. There is a good balance of hard (threshold) work and build or recovery (Z2) across each session and the week. I don’t feel wrecked in the way I have before but am getting better results than ever.