“It’s not Rocket Surgery, it’s Brain Science” - Coach Jim Partridge
Running a marathon burns about 3000-4000 calories. Most of the energy needed to run a marathon comes from burning fat-stores for fuel...and some glycogen (in the form of carbohydrates). Glycogen is like ROCKET FUEL.
Fueling is a big deal in a Full Marathon but it's actually a good idea in a Half-Marathon too. The pace (intensity) of a half-marathon is faster than a full marathon so you will burn through your carbohydrate energy (glycogen) a lot quicker than you would in a full marathon. It all depends on the intensity you run. Most runners can sustain race pace in a half-marathon without fuel (about 2 to 2-1/2 hours) but they may not realize how the body responds as it begins to run low. It's not like you suddenly run out of fuel but as the supply gets low your central nervous system (governor) will begin to restrict the flow as an involuntary survival response. You’ll begin to fade a little.
The same thing happens in a full marathon, your body will begin to restrict the flow of glycogen fuel as it estimates/predicts how much it will need to survive at that rate. That's why it's important to add fuel (in the form of carbohydrates) as you go. Eating (fueling) while running is difficult skill to master but pays off in a race. Keep in mind you can only absorb about 100-200 calories per hour (it's trainable) depending on body weight, type of fuel, metabolism rate, etc., yet you burn about 100 calories per mile (~600 cal per hour).
"It's like draining a bathtub with the faucet on; it will still run empty, just a little later." - Coach Jim
Obviously you don't need as much fuel in half-marathon as you do for a full marathon but it definitely will help. The timing of taking in fuel is the same as in a marathon, just less of it.
“Your body can only store enough glycogen to run very fast for about 60 minutes, moderately fast (think half-marathon) for about 90-120 minutes, and sort-of fast for about 2-3 hours (marathon), so you have to either add fuel or slow down to go longer and/or faster.” - Coach Jim
A good strategy might look like this; about 300-400 calories 3 hours before the start of a race, then another 100 calories within 5 minutes of the start. Continue to consume another 100 every 30-45 minutes during the race. Yes, that's a lot and it's not easy. Switching to liquid (gatorade) after 2-3 hours may help.
Try a few types of fuel (they're all good) during your long runs just as you would in a race. I prefer Honeystingers, and GU brands but even baked potato will work. Whatever you tolerate well. If you have trouble with them on race day, you can always slow down a little. Again, it's all about balancing your intensity (effort level) with how much glycogen your body can supply on longer runs.
Run at a pace where you reach complete exhaustion AT the finish line, not one step sooner. It takes good planning and a lot of practice to get it right.
There's more to it but that's basically how it works.
Glycogen = Rocket Fuel!
- Just for reference, remember this; 9-4-4 (and 7).
- Fats have about 9 calories per gram
- Carbohydrates 4 calories per gram
- Proteins have 4 calories per gram
- And for you drinkers...alcohol = 7
(these are approximations but still very useful)
Here’s a good RunnersWorld article on how to fuel your first marathon - https://www.runnersworld.com/fuel-school/how-to-fuel-your-first-marathon