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I did an interesting experiment this past week. (I use the term “experiment” quite loosely, of course, because I know there’s a very low degree of scientific rigor when comparing two workouts. There are so many variables that can’t be controlled, or even identified, and the sample size is about as small as it can get. But I’ve gotta work with what I have.)

There’s a run I’ve done a few times from my house in Longmont down the LoBo trail, around the east side of the Niwot Loop trail, then rejoining the LoBo to a turnaround point at the King Soopers in Gunbarrel. It’s a little over 22 miles for the out and back, and while there’s only 700-800 feet of climbing, the few hills there are help give a bit of variety to the leg muscles.

I ran it on 11/17, then ran it again today while taking a deliberately different approach to fueling and hydration.

Over the course of the 11/17 run I drank a little less than 50 oz of water and consumed about 400-500 calories. During today’s run I drank closer to 90-100 oz of water and consumed about 700 calories. I also took 4 SaltStick caps during the second run, instead of just 1 capsule during the first.

Even though I was weighed down noticeably more during the second run (since I ran with a Nathan hydration backpack) compared to the first run (where I ran with a single handheld water bottle), my overall pace was about 50 seconds/mile faster during that second run. Perhaps more significantly, my pace over the last 10 miles was about 75 seconds faster during the second run. All this while my average HR during the second run was lower than that on the first run (131 vs. 134).

While everyone knows that staying optimally hydrated will generally improve performance, it’s interesting (and really drives the point home) to actually see just how much that’s the case. (Of course, it’s possible to go too much in the other direction, and be so worried about taking in enough water that you find yourself struggling as you carry 8-10 pounds of water in your pack, have to deal with a sloshy stomach, or perhaps even face the dreaded hyponatremia.)

Now I’m wondering where that cross-over point is. What’s the ideal level of fluid and fuel consumption for my best performance at a particular distance? It certainly does seem to be distance dependent. For example:

  • I wouldn’t think about doing any run up to at least 75 minutes carrying any food or water.
  • I ran the Mt. Carbon Half Marathon carrying nothing, figuring that since it would be a 2 hour max run, I’d just make due with a few drinks at the aid stations, and that even if I slowed a little at the end, I’d still have a net time gain. That seemed to work ok.
  • I ran with a single handheld during the Quad Rock 25, and that worked out fine, but I was careful to drink each bottle before entering the next aid station, and the aid stations were relatively close together. It was also a very cool day, of course, so my hydration needs were probably a lot less than it would have been on a warm day.
  • I ran with one or two handhelds during the Tahoe Rim Trail 50 I started the race with 1, then picked up a second bottle at the 3rd aid station (the second visit to Tunnel Creek after the Red House loop). My calorie intake was limited to what I could fit in the pockets of my RaceReady shorts, which ended up being no more than 200 calories per hour. Clearly that didn’t work, as I crashed around mile 30. It was warm that day, but even if the temperatures had been friendlier I still would have had problems. I clearly had not taken in enough food or water to get myself to the finish in good form.

I don’t think I need to try to drink more on this local long run (at least not until we get back to spring and summer temps), but I think I’ll try to see how many calories I can take in before it starts to be too much.