After several years of experimentation, I’ve come to realise that my biggest trail nemesis is dehydration. One litre of fluids per hour with at least 1000mg of sodium seems to be the bare minimum in almost any conditions. If I’m messing with this formula too much, I’m virtually guaranteed to blow out after about three hours of running or riding.

Conversely, when I take enough electrolytes and fluids, the amount of carbs I’m eating doesn’t seem to matter all that much. Anywhere between 40 to 120 grams per hour seems to work just fine, and I don’t feel any practical difference in terms of fatigue, gut comfort, or recovery as long as I’m somewhere within this range. This anecdotal evidence makes me think that the so-called “carb revolution” in trail running is at least partially explained in terms of hydration rather than carbs: when you’re eating more carbs, you’re also usually drinking more, which means that it’s difficult to disentangle the effect of carbs from the effect of being more hydrated.

On this week’s long run, which was about 30K in typical sunny but not too warm San Diego conditions, I carried one litre of fluids with me with approximately 1500mg of sodium. My original plan was to fill my bottles in the middle of the run as I was doing loops in a park, but I never got around doing so as I didn’t want to break the rhythm of the run. Consequently, I got completely dehydrated at the 2.5 hour mark and had a pretty rough jog back home.

Usually, it takes me at least 24 hours to come back from dehydration. However, since I had another long-ish run planned for the following day, I rehydrated aggressively in the evening, drinking approximately 6 litres of fluids (mostly water and tart cherry juice) with at least 2000mg of sodium in total. I was still expecting to feel terrible during the following day’s run but, instead, I felt totally normal! Notably, not only did I feel great in terms of being hydrated, but I also didn’t feel any fatigue or aches in my legs. To me, the lesson from this week is that I’ll need to come up with (and stick to) a hydration protocol not only during runs but also before and after.