Some interesting thoughts have emerged from two x 10Klm runs that I have done over the last few days.
Both runs were done using run/walk strategy - the yellow one on the graph was done today and the blue one a few days ago. The yellow one was done in the company of some other runners, at a 60sec/30sec run/walk ratio, and averaged 7mins:30 secs per klm over the 10K. I was just about "finished" at the end of this one - perhaps because of the very big hill at the end. I recently completed a 21.1 klm half marathon using the same run/walk ratio as the yellow trace and at almost identical pace per klm. I was absolutely finished at the end of that run.
The blue run was done a few days ago -- by myself, at a 30sec/30sec ratio , was much more relaxed, and I was not exhausted in the least at the end. I could easily have gone further than the 10K. The average pace of this blue run was 30 seconds per klm slower than the yellow one -- at an average 8 mins per klm.
The difference between the two runs in terms of my heart rate is obvious . Each vertical division on the graph represents `10BPM -- the reduction in HR during each 30 second walk cycle seems to be about the same for each -- but the 1 minute run cycle of the yellow run escalated my HR over the course of the 10K quite a bit higher than the blue run (an average of 20BPM) - and I could definitely feel that at the end of the run.
Over the course of a 21.1 klm half marathon, this reduction in pace would cost me an additional 10 minutes in finish time - ie my recent HM would have been 2hours 46 minutes instead of 2hours 36 minutes, but as I am purely a recreational runner, this would not concern me. It does interest me though that perhaps I could, sometime in the future, further the distance undertaken past that 21.1 klm "limit" which I could not conceive doing at the finish of the HM