First, you need to understand that the primary purpose of training long is not to just make you tougher when faced with the Fatigue Monster (see last week’s blog), though that’s definitely in the top three. No, along with a whole host of really neat physiologic changes (well, I think they’re neat), you teach your body to store more glycogen (energy sugar) in the muscles and train your energy system to burn that glycogen more efficiently along with fats. The ability of the muscles to propel you down the road or trail for prolonged periods is strongly influenced by the amount of carbohydrate stored in skeletal muscles, with muscle glycogen depletion becoming the decisive factor limiting prolonged exercise.
By far, carbohydrates are the #1 choice for fuel by the muscles, but our injector system only stores enough glycogen in the muscles, liver, and blood to get us a little more than 2/3’s of the way down the marathon road (can you say WALL?). Running out of glycogen presents an enormous threat to your muscles’ survival, so when you train long and the fuel gauge creeps towards “E”, the muscles start sending up rescue flares and a very strong signal is sent to cause 3 things to happen:
1) Your brain says to your muscles “Hey, I’m not exactly sure what the heck he’s doing, but he may do this again”, so more glycogen is made and stored in your muscles than what was previously present, thus putting out the fire of the threat and increasing endurance for future efforts. Research shows that the more your glycogen tank is emptied, the faster and more it’s refilled. That’s a good thing, because the more glycogen you have packed into your muscles, the greater your ability to hold your marathon pace to the finish. To create the largest muscle glycogen storage possible, you need to deplete muscle glycogen on a regular basis.
2) Your muscles are forced to rely more on fat as fuel, making them much more effective at using fat for energy. No matter how thin you are, you have oodles of fat. The problem is that muscles like the rich, high-octane stuff, not that low-grade, hard-to-burn fat. But, the better your muscles are at using fat for energy, the longer it will take to run out of your limited store of glycogen and the less your pace is going to slow toward the end of the race. You need 100% energy and so you go further burning 50% carbos than burning 80% carbos.
3) Your very smart liver, sensing that muscle glycogen and blood glucose are low, synthesizes new glucose from non-carbohydrate sources, namely amino acids and lactate. The new glucose is then used for energy so you can maintain your marathon pace.
So, when you down those gels, or some other form of sugar energy during your long training runs, providing muscles with a ready fuel, you blunt all three of the above adaptations. To maximize your physiological adaptations, it’s better to cut down on your “topping the tank”. I teach my runners to take no more than one gel during a training long run (usually at the midpoint) and drink mostly water instead of gulping down a sugar drink every 2-3 miles. With this method, your energy system won’t expect a constant jolt several times along the way.
Now, in the marathon itself, however, you do want to consume carbohydrates since it’s important to maintain blood glucose levels for as long as you can so you can use it as fuel. First, energy will be derived from the glucose in the blood, then the muscles, and finally, the liver. Of course, there’s some overlap, but basically, that’s the pecking order. So, you begin ingesting your first gel at about thirty minutes, and then about every 30-45 minutes after that. If you drink an energy drink at the aid station, don’t “Sugar OD” by adding a gel. You can only absorb about 240 calories of carbohydrates an hour, so based on about 100 cal/gel, two gels an hour is about it. More than that…well, don’t complain to me if your tummy starts to feel like a giant Boy Scout knot.
Running a long distance is a series of doing things right, cutting corners when you can, and not going down the “I’m different than the average runner” road. I strongly believe that a steady flow of injested carbohydrates during the event will help your outcome, but you can tilt the odds in your favor with some solid fuel planning in the months and weeks before you toe that starting line. Train smart my friends.