Fasting and Running Performance
A week ago, my friend Jason Robillard posted some interesting anecdotes about his training for the Western States 100. As part of his preparation for the race, he is maintaining his normal training schedule while fasting (going without food) for 12-48 hours at a stretch. His plan is to mentally and physically train his body to run even in the absence of victuals.
O yes. It sounds dumb. But he’s actually a very intelligent, thoughtful person…
He’s just a little crazy is all. You can see his post HERE.
This is not a commentary on Gruisinger’s theory of anorexia and evolution. Maybe later….
Here is an excerpt from Jason’s post:
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) [good thinkin Jason...], 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.
Drum Roll Please….
Here is the explanation in one sentence: FASTING RELEASES HORMONES THAT ENHANCE THE UTILIZATION OF GLYCOGEN DURING EXERCISE.
Allow me to explain. In the absence of carbohydrate consumption, there is no new glucose being added to the blood. Every cell in our body needs glucose + oxygen to function. Take one of those ingredients away and, POOF! Dead. Gone….
Since glucose is worth one half of the equation that gives us life, glucose metabolism is very well controlled physiologically. Hormones like insulin, glucagon, cortisol, growth hormone, and epinephrine all have critically important metabolic effects.
In times of plenty, the hormone insulin causes the body to store excess glucose in the form of triglycerides (1/2 a glucose molecule attached to long hydrocarbon chains called fatty acids) and glycogen (huge macromolecules formed by thousands of glucose molecules all bound together). Triglycerides are stored in fat cells. And Glycogen is stored primarily in the liver and in muscle cells. There they stay until there is not enough new glucose entering the blood from digested foods….
Or until you go on the Atkins Diet….
When food is not plentiful, carbohydrate intake is reduced, and during fasting, insulin levels decline and other hormones dominate the metabolic scene. Glucagon, Growth Hormone, Cortisol, and Epinephrine are the primary players here. They break down triglycerides and glycogen, releasing the stored glucose into the blood. So, when there is no new glucose from consumed food, the cells release stored glucose to sustain the body during times of fasting or carbohydrate restriction.
OK. Now to answer Jason’s question…
After a short term fast, before glycogen stores have been used up to sustain the basic functions of life, the effect of fasting on exercise performance is to enhance the breakdown of glycogen and triglycerides. In a short-term fast, stored glucose is released more efficiently during exercise – thus the feeling of more energy in a shorter run.
But this also means that the storage tanks will be used up faster. There may be more energy in the short term. But try this on a longer run, and you’ll hit the wall sooner. Endurance exercise can be sustained for longer periods when food is consumed regularly.
Run With Brains,
Scott Hadley PhD, DPT