I didn't have very long for a run so long and slow wasn't an option. I often state that I need to work on speed so an interval session seemed to be a good idea. I completed my usual circuit around the local woods but with a 45 second 'sprint' every few minutes. It's quite an undulating circuit so I tried to do the intense part on ascents and have gentle descent. Fast downhill seems associated with injuries!
The post run data shows the interval pattern clearly when shown as Grade Adjusted Pace for each interval but the heart rate data had little relationship with my effort. Early in the session it was very high, later it was low. Optical heart rate recording isn't reputed to be good and in this circumstance it didn't work well.