Ask the Coach
Dizzy after 20
I have done several 50K runs, but even during training, I start to feel like I have vertigo after about 20 miles. I don't feel excessively fatigued but, rather, dizzy. I've been told that this is a fueling issue and that I need more protein. I'm a vegetarian, but very conscious of my protein intake. What causes the dizziness?
—Rebecca Dusseau, Eugene, OR
Such a sensation is common among ultrarunners. Low consumption of protein isn’t a likely factor, though. However, being a vegetarian means a B12 deficiency is possible. According to Benjamin R. Lewis, M.D. from the University of Utah, “If Rebecca is anemic, a consequence of B12 deficiency, she’ll certainly feel light-headed and fatigued.” To combat this, add some B12 to your diet; vegetarian sources are few, but try kombucha and nutritional yeast.
Dr. Lewis says your issue is “most likely hypoglycemia, since your symptoms don’t start until you pass 20 miles. You’re probably transitioning to burning fats right around that time.” Hypoglycemia is a condition caused by a drop in blood sugar (glucose), and a large drop can cause a per- son to slip into a coma or go into cardiac arrest.
Dr. Lewis suggests three main fixes for hypoglycemia: “Become better at burning fats, store more liver and muscle glycogen and eat smarter on the run.” Your body gets its energy from three sources: ingested carbohydrates (e.g. gels); intramuscular and liver carbohydrate stores (glycogen); intramuscular and adipose fat stores (badonkadonk or “spare tire”). At rest an elite endurance athlete typically metabolizes less than 40 percent of their energy from carbohydrate. Due to an ultrarunner employing a comparatively slow pace and lower intensity, fat stores become the preferred energy source.
There are two well-accepted techniques to becoming more fat adapted. During the base training phase, employ a low-carbohydrate diet and spend the majority of your training time doing easy, steady-state efforts. The second way is to train in a glycogen-depleted state, which forces your body to use its fat stores as fuel. The easiest way to do this is running first thing in the morning, before you eat, to assure your glycogen levels are low.
Your issue could also be just getting behind on caloric consumption. Try to eat a gel (or other preferred carbohydrate source of about 100 calories) every 20 to 30 minutes and see if that fixes the issue.
Because training depletes glycogen stores, replenish them right away (within 30 minutes post-run) to train your body to store more on- board energy.