A medium tempo/speed effort on the treadmill out at 3 to 4 minutes per rep with only 30s recovery between sections. My heart rate was heading towards 170 during the last few reps and wasn't really recovering much during the recovery. Being part of a group session of 60 or so other runners really kept me going though. It's easy to abort a solo session when you've had enough but somehow being part a group session, albeit a virtual one, provides that impetus to see it through. A good 42 minutes training ticked off.