ornoth | Defing the Natural High

In preparation for my annual charity bike ride in August, yesterday I did an 87-mile ride.

One of the things that you’ll often hear from athletes, particularly endurance athletes, is the “natural high” that comes from pushing the limits of physical stamina. Is there really such a thing, or are they just talking out of their collective asses?

When you exercise, your muscles are fueled primarily by muscle and liver glycogen and blood glucose. Glucose is used in preference to other energy sources because it can be stored right in the muscles, doesn’t need to be converted into anything else, and can support both aerobic and anaerobic effort.

However, the body can only retain enough glycogen to power about one to three hours of exertion. Once you start depleting your glycogen stores, your muscles also tap into stored fat and protein for power. However, fat can only provide energy in the presence of glucose, and only at lower intensity, aerobic levels of activity. Converting protein into energy is also an inefficient process, and the body tries to avoid it.

So why not just eat something during a ride? Well, you can definitely benefit from high-carb snacks and sport drinks, and those should be built into any endurance athlete’s event plan, but you need to be very careful what you eat and how much. If you eat too much, your digestive system takes blood away from your muscles, where the athlete needs to use it to supply oxygen and remove lactic acid. Eating can definitely keep you going, but until you stop exercising, eating can’t replenish your depleted glycogen stores.

All this adds up to one thing: in an endurance event, an athlete will rapidly deplete his supply of glucose and maintain that depleted state for an expended period of time.

What’s that got to do with getting high? Well, the brain works on glucose, and unlike muscles, it cannot store any. Even worse, your brain can’t make use of fat or protein at all. So your brain is dependent on the one fuel that is most highly demanded by your muscles.

In an endurance event, athletes are essentially starving their brains. That’s why you’ll see marathoners or other athletes acting punchy at the end or after an event. The dwindling supply of glucose to the brain leaves them with symptoms like impaired judgment and reaction time, sleepiness, disorientation, and irritability.

Cyclists call this state “bonking”, but that usually refers to the loss of physical strength that comes with glycogen depletion. However, at the neurological level, the athlete has also undergone a temporary chemical impairment of function that results in an alteration of their consciousness that is very similar to intoxication.