4.50m at the Treadmill (repeats)

4.50m @ 8.61 pace w/ Avg HR of 153 (Zone 2 or 78.2% of max)

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9.53/154
7.53/164 - Repeat interval of 1m @ 7.5 pace
8.50/158 - First half was recovery (9.5), second half was first half of next interval (7.5)
8.43/158 - First half was interval, with the last quarter mile increasing in speed up to 7.25, 2nd half was recovery
4.74/152 (9.48 pace) - Recovery

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This was the 2nd highest HR Efficiency number that I've ever recorded (3/30/09 was top).

Interesting that the HR numbers never really climbed, even though I pushed that 2nd interval some at the end. I've sort of wondered about these treadmill workouts being too easy, and even if the 'mills themselves are calibrated properly. My best runs from an "HR efficiency" perspective have all been treadmill runs. There's something to be said for being indoors in a climate controlled area and having the machine set the pace for you...and I've always found running on a treadmill "easier" than outside.

Still, I think I'll try to rotate around to different ones and see if I notice any difficulty changes.