Fueling Up

Base miles season is here again, and with longer rides comes the need to focus on calorie replenishment while training.  A Ferrari will only go so far on a tank of gas, once the tank is empty even the fastest most high performance automobile will sputter to an untimely stop.  The human body is similar, but with a big difference: we have a huge reserve tank (fat stores) but that tank is attached to the engine with a tiny hose and fuel is administered in drips and drops.

Energy for the human body comes in three forms: carbohydrates, fats and proteins.  These are called the primary macronutrients.  In order to be usable these three energy sources need to be broken down (i.e. metabolized) into glucose.  Fats and proteins can be broken down into glucose, but it’s a slow energy consuming process, carbohydrates, on the other hand, can be quickly converted into precious glucose.  When it comes to fueling during exercise carbs are our friends.

The body doesn’t store glucose but instead banks extra glucose in the liver and muscles in the form of glycogen.  The typical human body stores enough glycogen in the liver and muscle tissues to fuel approximately ninety minutes of moderate to high intensity exercise.  Glycogen is the body’s go to energy source.  When the glycogen stores become depilated the body begins burning fat for energy, even the thinnest person has enough fat reserves to fuel days of low intensity exercise, but the key words here are low intensity.  Burning fat trickles the energy to the working muscles, in other words it’ll keep you going but at a much reduced pace.  When you begin to rely heavily on fat reserves for energy you’ve “hit the wall,” you’ve “bonked” (notice how bonking doesn’t leave you dead on the side of the road, but instead reduces your speed down to “I’m going nowhere” levels).

Bonking isn’t inevitable, you can avoid it by having a well thought-out nutrition plan designed to continually replenish your glycogen stores – kind of like continually stopping at gas stations on a long road trip.

Unfortunately developing a nutrition plan isn’t as simple as eating the calories that you burn.  A calorie is only useful if your body can break it down and absorb the energy via the digestive tract while maintaining a high level of physical exertion.  Here is the key problem: the harder you work the more you need the energy, but, conversely, the harder you work (i.e. the higher your heart rate) the slower energy is released via the digestive tract.  In other words, as your heart rate goes up the slower energy is released from your gut.  If you keep shoveling food into a slow digestive system you’ll end up with GI distress, a condition nearly every endurance athlete is all too familiar with.

The trick to developing an on the bike nutrition plan is to figure out what works best for you.  In the next series of posts I’ll throw out some ideas on what has worked for me and what hasn’t, but in the end every body is different and you’ll have to experiment to find out what works and what doesn’t.