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Four kilometres into this morning’s planned 30 kilometre run, I lost all energy and felt like I’d hit the wall. The pace I could maintain was drastically reduced, and slight undulations became mountains.

I believe that the cause was hypoglyc(a)emia – low blood sugar. I’ve experienced similar symptoms in the past after drinking Sprite or Fanta immediately before a run. The body’s insulin response to the influx of sugar is complicated by exercise. This morning I had my usual pre long run breakfast of toast and jam, and also had a glass of sport drink which I mixed myself. It is probable that I was overly generous both with the jam (sugar is the first named ingredient) and with the amount of sports drink crystals which also have sugars as their main ingredient. What is certain is that the time between consumption and running was much less than usual.

I decided to continue running at a reduced pace in the hope that my body would resolve the issue. By the eleven kilometre mark, I was effectively back to normal. In fact, so normal was the run that I consumed the first of two gels at about 19 ks.

Two lessons were learned from this. The first is to be more careful about what and when I eat and drink before a long run or a race. The second is that it is possible to recover from a moderate episode of hypoglycemia during a low intensity training session. (My previous episodes were years ago, and I think that I just called the sessions off.)

Update, 20 September 2015. Perhaps the lessons weren’t learned, because it happened again today. Very similar, toast and jam consumed less than an hour before starting and a glass of “no added sugar” orange juice very soon before going out the door.

Update, 2022.  A close relative who happens to be an endocrinologist does not agree with the self-diagnosis above.