Every runner knows that both nutrition and training affect performance. Most runners think of these two influences as being fundamentally separate, affecting performance individually in different ways. But nutrition and training aren’t really separate at all. Your training influences how your diet affects your body. Likewise, your diet influences your training capacity. To maximize your running performance you must ensure that your training and nutrition practices are aligned to serve the same objective. I refer to this concept as nutrition-training synergy.
The major shared objective of the training and nutrition components of marathon and half-marathon preparation is to push back the wall—to give you the ability to sustain a chosen pace through the entire race without losing momentum in the last few miles. We have thoroughly explored the nutrition side of nutrition-training synergy. It’s now time to talk about training—specifically, how training can cooperate with nutrition to push back the wall, and the best way to train to ensure that your glycogen stores last all the way to the finish line of your races.
Training is capable of pushing back the wall in several different ways. First of all, effective training increases aerobic capacity, or the body’s ability to use oxygen to release energy from carbohydrate and fat. The details of how an increase in aerobic capacity improves marathon and half-marathon performance are complex and not fully understood. The general idea is that an increase in aerobic capacity enables a runner to draw on the body’s total energy resources at a higher rate, and thus run faster, without hastening glycogen depletion. Elite male runners whose marathon race pace is under 5:00 per mile burn carbohydrate at a higher rate than do middle-of-the-pack runners who run marathons at 10:00 per mile. But thanks to their higher aerobic capacity, elite runners are able to derive more usable energy out of their carbohydrate fuel supplies, so they are no more likely to hit the wall than slower runners despite using more carbohydrate.
Proper training also lowers the total energy cost of running a marathon or half marathon, and it does so in a couple of ways. First, training tends to reduce body weight. A runner weighing 154 pounds burns approximately 2,950 calories during a marathon. If this runner loses 5 pounds he will lower the total energy cost of running a marathon to approximately 2,854 calories, thereby reducing his chances of bonking due to glycogen depletion. A second way that training lowers the total energy cost of running a marathon or half marathon is by improving running economy, or reducing the amount of oxygen and energy that are required to run at any given pace. As running economy increases, the body’s fuel stores are able to stretch farther.
Yet another benefit of proper training is an increase in the amount of glycogen the muscles and liver store. Obviously, the more glycogen your body contains, the longer this crucial energy source will last, even if the rate at which it is used doesn’t change. After tapering, a trained runner’s body stores roughly twice as much glycogen as does a non-runner’s body.
Finally, and not least important, effective training increases the muscles’ capacity to burn fat at higher intensities, so that more glycogen is spared when you’re running at your goal marathon or half-marathon pace. This effect of training is related to but not completely accounted for by increases in aerobic capacity.