I’m in the process of doing periodic fasting as a training method for running a 100 mile race near the end of June. It is a training method I’ve used in the past with great success.
I will go about my normal training routine without eating anywhere from 12 to 48 hours before beginning exercise. In most cases, the training involves intermediate runs of 10-20 miles. The fasting creates a dramatic shortage of glycogen. The result- I hit “the wall” much earlier in a run.
This has two positive training effects. First, it mentally prepares me for the feelings leading up to and during this low point. Being able to confidently predict the feelings helps prevent a low during races as I can consume carbs as soon as the early symptoms appear. Second, it seems to acclimate my body to the experience, making it less severe. I suspect it has something to do with training the body to utilize fat stores during exercise. My physiology expert friends could probably give a better explanation.
The experience of this glycogen-depleted training run is predictable. The first few miles goes fairly well. At about mile five, I start feeling fatigue. By mile eight I experience fairly significant mental fatigue. By mile ten I’m a wreck. This feeling usually lasts for a few miles, then slowly subsides.
The Weird Unexpected Run
Occasionally I experience something altogether different. This happened on a training run this last week. I had fasted for about 24 hours, eaten about 500 calories (beer, Doritos, and jalapeno peppers), slept, woke up, ran a three mile tempo run and crosstraining routine in the morning, then did a 7+ mile hard trail run later that night. By the time I ran the evening run I had consumed 500 calories in 48 hours. Based on previous experiences, the trail run should have been exceedingly difficult.
But it wasn’t.
It was quite easy. I managed to maintain about an 8-8:30 pace for the majority of the run. At about mile 5.5 I slowed down due to some mild fatigue and a sore foot. Since the Mind the Ducks 12 hour is coming up, I didn’t want to risk injury. Based on the effort, I should have hit a serious wall very early in the run. Instead, I felt great. My energy level was akin to slamming a few Redbulls 10 minutes before the run.
This isn’t the first time I’ve experienced this phenomenon. I’ve tried to predict when it happens, but that proved to be difficult. There does seem to be some pattern in regards to pace- the higher the pace the less likely I experience the hard crash… at least for runs under 10 miles. I’ve never attempted a hard, long run when fasting.
I’m always curious about physiological processes, especially those that seemingly defy logic. This fits the category. Why did I feel so good when I shouldn’t have had enough energy reserves to run at that pace for that long and feel as good as I did.
One possible explanation popped in my head. A few years ago, I came across a theory about anorexia. Shan Gruisinger, PhD., a clinical psychologist, proposed a theory that anorexia may be an evolutionarily-developed genetic trait that helped primitive nomadic humans survive.
According to the theory, anorexia developed as an adaptive trait when groups of humans ran out of food in one location. Normally humans are overcome with fatigue and obsessive hunger, which limits their ability to seek out new food sources. We’d curl up in the fetal position and slowly starve. People with the “anorexia” disposition would do the opposite- they would become more energetic and/or manic, have a compulsion to move, and lead the group to new food sources, thus allowing the group to survive.
Gruisinger’s theory certainly explains some common anorexic behaviors such as the compulsion to move, exercise, and food refusal. All of these behaviors would be adaptive… if they were used to seek out and feed a group of nomads. In modern society where food is plentiful, the behaviors are maladaptive to the point of being dangerous.
Could Gruisinger’s theory explain why I seemingly had more energy on this hard trail run? If so, what are the physiological processes responsible for providing so much energy? For five miles, I was running hard enough where talking was difficult. Based on my heart rate, my body couldn’t have been utilizing fat stores during that time. What about the genetics? If this theory holds true, do I have an “anorexia” gene? Based on ALL my past behaviors, I seriously doubt this to be the case.
Could this theory explain a sub-set of individuals that suffer from anorexia… perhaps anorexia athletica? Why does this seem to affect females more than males? Is it a case of reporting bias? Or would women somehow be better at finding new food sources in primitive societies (foragers versus hunters), thus more likely to have survived and passed the gene via natural selection?
So many fascinating questions… so few good answers.
What are your thoughts? Have you ever experienced something like this? What about Gruisinger’s theory? Does it have merit? Share your thoughts!