Thank you. Makes sense regarding delay. That was my guess too. Body does not believe that could have been a Zone 3 run. Don't have a chest strap. Not important enough to me to buy one just now. Highest priority: get healthy and strong enough to do sessions like this regularly. Thanks for stopping by.
Your body is right to call that harder than Zone 3. For short sprints, RPE and your splits tell the story, while wrist HR lags and the long walks pull the average down. If you want cleaner zone data, try an easy jog between reps and wear the watch snug, but the real win is staying healthy and repeating the work. Keep stacking sessions when you feel fresh and your speed and durability will both rise.