Sunday, October 7, 2018

A tale of two runs

Or, what a difference two hours earlier and 15 degrees cooler make!

Now that just a hint of fall is in the air, and that dripping hot August 5th 19-mile run is far enough away in the rearview mirror, it seems a good time to replay it and see what changes I should make for the next time in similar conditions. The following two figures are of the run’s pacing and map, respectively, from my TomTom Spark 3 Cardio watch.




Basically, I hit the wall--at Mile 8. The entire run just felt different. Temperature at finish was 91F, with humidity still near 80. Looking back, obviously, I should have started earlier that morning--by at least couple hours. It wasn’t quite heat exhaustion during the back half of the run; but there were perhaps intimations of it. Dehydration? Probably. The usual 22 oz Nathan bottle I carry on long runs definitely wasn’t enough. And, had I not fortuitously run by a water fountain at a local park, I would have run dry and likely run into trouble. Definitely need to better plan for refills! Before the shower, the scale showed a seven-pound weight loss, which seems to be within the average of two pounds of sweat per hour of intense activity. The recovery of the lost pounds was fairly quick, as typical, within a couple days or so.



The entire run felt different, but the back half decidedly so. I was into some new, Twilight Zone-like territory. Ears felt waterlogged. Voice sounded foreign. Skin grew a layer of salt crystals. It didn’t even occur to me at the time that, being evidently a salty sweater, my body was running low in sodium.



In previous hard runs, my legs would partially recover by walking, and I’d be able to run a stretch before the next walk. This time, the legs didn't recover by walking; they continued to feel fatigued. In my mind at the time was the Potomac Marathon coming up in five weeks; so, I decided to not chance it and walk the last three miles home. Over the back nine miles, I walked about half that distance in total. Cadence (stride rate) was 142/min; usually it’s 168-174. Total time was about an hour longer than usual for 19 miles.



The body acclimates to heat, from a number of physiological adaptations, including integrated thermoregulatory, cardiovascular, fluid-electrolyte, metabolic and molecular responses, over a period of about one to two weeks. (See, e.g., Armstrong, 1998Nielsen, 1998Prazak, 2014Sawka et al., 2016; and Chong and Zhu, 2017, a review.) So, if I had run the 20 miles on August 12th in similar conditions, I probably would have done better. (August 12th was over the same route, just a mile longer.) But, by far, the big difference between the two runs of August 5th and 12th was 15-degree cooler! The result was a two-minute faster average pace. (For comparison, the July 29th run in California was done in cooler and drier conditions.)



The following nomogram from Cheuvront et al. (2010) shows the effect of temperature on marathon pacing. My pacing as a function of temperature accords fairly well with the chart.

If endurance, according to Alex Hutchinson in his book, Endure: Mind, Body, and the Curiously Elastic Limits of Human Performanceis “the struggle to continue against a mounting desire to stop," then I lost that struggle on August 5th. Perhaps, in such conditions, I should have stayed closer to home and run my usual long run route (three miles from home at its farthest).

In fact, such a struggle was the August 5th run that, for the first time ever, I made a nine-minute Starbucks pit stop at around Mile 18 to get coffee; which greatly helped getting me through that last mile! (Btw, my TomTom watch has a nice auto-pause feature, which produces an average pace based on actual activity, not including, e.g., time in a Starbucks getting coffee.) The guy who made it to the barista just ahead of me had some kind of complicated order. With my ears "waterlogged," I only caught a few words: can you add ... caramel ..., I can't do that, but I can ... Standing right next to him, I was thinking, hey buddy can you hurry up I just want to order a tall coffee and get out of this way-too-air-conditioned place (for a sweat-soaked runner). I suppose I was fortunate, the way I must have appeared, that the police wasn’t called on me. But, then again, if my skin had a somewhat darker hue from all those summer months of running ...