Provo Canyon. Tempo run - standard 3 miles. Odd thing happened in the warm-up. It was cold, resting HR while driving was 48. However, as soon as I started running it jumped to 130, and I felt like I could run fast right away. Ran uphill at about 7:10 pace for 2.25 miles to the Nunns Park. The tempo run went rather odd. First 1000 fairly relaxed in 3:22, HR still climbing to where it is supposed to be. Then I felt good and started pushing. Hit the mile in 5:17, which was about 5:09 pace for the next 600. HR climbed to 160. However, on the next mile, instead of climbing to 163 it stalled at 160, even dropped to 159 occasionally, and I felt like if I went any faster the pace would not be sustainable. Next mile in 5:23. On the last mile I managed to shift gears a bit and get back up to 5:20. It was flatter (0.5% grade down), so this required HR of 162. Kicked on the last 300 in 57 to dip under 16:00. HR climbed to 168 during the kick, but then dropped to 167. Total time 15:58. It is tempting to explain the struggle on the second mile as a consequence of going anaerobic during the second half of the first. Perhaps this is true to a certain extent, but with a twist. A normal anaerobic backlash for me (as observed during and after Veyo in St. George) should see HR climbing to 166 or higher and staying high while I recover at a slower pace, then dropping back to the pace-appropriate HR. In this case, I believe I did go anaerobic, but not so much because of the pace (5:09 down 1.5% grade should not throw me severely anaerobic), but because the heart could not respond quickly enough to the change of pace. So it was anaerobic after all because I ran that fast with the HR only at 160, and I was paying for it later for the rest of the run. The lesson to learn from that is when it is cold, or if the heart is struggling to get going, hold the legs back until the heart is ready. During the cooldown met a guy named Reed. We chatted a bit. I dropped him off and decided to run another mini-tempo uphill. Started at the mouth of the Provo Canyon and ran 1.5 miles up in 8:28 at a fairly steady pace. HR hovered around 162 once I warmed into the pace, and briefly maxed at 166 on a steeper grade towards the end, then went back to 163. I felt a lot better this time, even thought of going the entire 3 miles, but unfortunately did not have the time. Ran with the kids in the evening. | 