Run, but you can’t keep up: calorie deficit

I got the bus down to Newcastle on Sunday to do another long training run. This time it was logistically easier, and more prudent to focus on the difficult part of the course: Tollymore and Donard. I started at the half-way point in Donard Park and followed the MWM route to the exit of Tollymore Forest, before turning around and coming straight back again. When I reached my starting point, I then set straight off up the big climb again, before running down to catch the early bus home. 33km, over 1100m ascent /descent in just over 3.5hrs. 

It was a great run throughout. No hills were walked, descents were controlled but not leg-shattering, and my pace was very even: I actually managed to return from Tollymore slightly quicker than I set out. It was one of those great training sessions when you suddenly start to see the results of the hard work. My new nutritional strategy also seemed to be playing a part. Having got on well with 1 gel/hr on my last very long run, I ramped it up to the recommended 2 gels/hr this time (along with 4:1 powder in my bottle). I tried a few different brands of gels, which I shall review separately. As before, they all went down easily, caused no stomach problems, and my energy was constant.

It seems too good to be true, and looking at the figures reveals the catch. Here are the facts:

  • Expended 3760 calories
  • Consumed 1570 calories
  • Lost 1kg weight
  • Not dehydrated (frequent clear pee and constant performance)

There are two things to note about those facts:

  1. Between weigh-ins at home, there were probably another 3.5 hrs of bus travel (non-running). We could assume around 100cal/hr also burned in this time taking the total expenditure for the period to approx. 4100 calories.
  2. The body can only absorb up to 280 calories/hr when running, so initially my figure for consumption does not add up. This includes an instant oat drink and a carb drink taken before the run started, and a 4:1 drink taken on the way home to aid recovery. Together these account for around 6-700 calories, so the remaining 900 falls within the range of the possible for ingestion during my 3.5hr workout.

All-in, that leaves me with a 2500 calorie deficit, and a 1kg weight loss not attributed to dehydration. That means I either burned fat or body glycogen.

At 9cal/gr, it would only take 278g of fat to supply those calories. Perhaps it was fat, and a 700ml loss of water… less than 1% body weight and not enough to notice any affecting of performance…the frequent pee-stops a side effect of high caffeine in the performance foods?

As glycogen contains 4cal/gr, but is also bound to approx. 3gr water per molecule, the 2500 calories would have equated to a 2.5kg weight loss as the bound water was released. The 625gr glycogen is probably more than my body can store anyway (4-500gr), so I would be completely depleted: I would ‘bonk’, ‘hit the wall’. My muscles would be stiff and sore and I would have trouble moving. 

This clearly wasn’t the case, so it must be a combination of the two… perhaps 200g of each fuel:

  • 200g fat = 1800 calories
  • 200g glycogen + 600g water = 800 calories
  • 1000g total = 2600cal total

Where is the problem you say? I’ve assaulted you with figures, but they all add up and I said I was fine. Indeed, I was; but when we extrapolate out to an ultra-distance run we hit a hard truth… I cannot consume as many calories as I burn, and I will run out of glycogen at that pace. Other factors aside, I could only perform at that rate for around 7hrs. Not long enough for the 9hr time to finish the MWM at that pace (purely hypothetical), and it certainly becomes crystal clear why I went so badly downhill last year when consuming less than optimal foods.

That is why you carb load for a week beforehand. That is why you start eating from the beginning of the race. And that is why you try to burn more fat by taking the pace super-easy for the 1st half and not bounding up hills! Lesson learnt.

There are still over 5 weeks to go. If I lose some excess weight I will require less energy for any given pace, and if I run 10% slower I should also be able to rely more on fat to stretch out the glycogen reserves and still achieve my dream-ultimate-goal of a 10hr finish.

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