30 k fasted run – March 5, 2016

Okay, so I have established that I am not a blogger – at least I don’t seem to be able to get words down in a timely fashion. But I still have a desire to create some record of my experience in a roughly chronological fashion, so I thought I better just get this post done…

I have been doing what I call fasted long runs for the last month or so. Essentially they are just weekend long runs without eating anything before or during, which translates to about a 10 – 12 hour fast pre-run. As I am in a building phase after the off-season, I have been slowly adding mileage every week, mostly to the long run: from 21 k through the winter and into January and up to 30 k this morning. In addition to the training component, in the last 5-6 weeks I have also reduced my carbohydrate intake to average less than 100 g per day. This is carb net of fibre, not total carbs. Also, I am not being anal about tracking this, but it errs to the low side (more on this some other time).

I’m really interested to see what the effects of diet are on potentially increasing fat-metabolism and how this will effect nutrition needs and long efforts. I have this idea that I can test this by running fasted. I also have a theory that running fasted will teach my body to do this better. Perhaps this is foolish, but I don’t really know.

I have been mostly running “fasted” through the winter, with consistent 21-22 k distances on Saturdays, which last less than two hours. I would say that these were generally pretty comfortable efforts with some normal variations based on sleep, rest and what else has happened during the week. I would consistently start to notice that around the 16-17 k mark I would start to notice a lessening in “vigour”. Not exactly fatigue or energy depletion; more of a mild brain fog and a diminishing desire to keep moving.

In the 5-6 weeks of low-carb eating, I have noticed some challenges that are new. I’m not completely sure that diet is the cause as it has also coincided with my decision to have a standing desk at work, but essentially, I am experiencing increased “muscle fatigue” during runs. It manifests as what I would have called lactic acid burn in the past – and perhaps this is what it is. It has generally been present during most runs, “a lot of the time” but it is particularly noticeable when climbing. It’s interesting because from a heart rate perspective, climbing should be easier than it has been – my heart rate seems to take longer to elevate during climbs. Muscularly, though, it is much more difficult and this tends to be consistent throughout the run, pretty much right from the beginning. The bottom line is that since lowering the amounts of carbs in my diet, my cardiovascular system feels pretty relaxed during runs but muscularly it has been less comfortable.

The 30k fasted run today was the first time (roughly) since I consciously cut carbs, that my body (muscularly) felt pretty good. Today, I felt energetic from the get-go and the fog began around the 24k mark.

I’m hypothesizing that my body has been adapting (or trying to adapt) to a new normal: one with significantly less carbohydrates, and this will take some time. I have no idea if this is accurate and if so, how long it will take, or even if my body will ever find a happy place with this new regime, but perhaps today was indicative of turning a corner? Only time and consistency will tell.

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