As Tim Noakes, MD, wrote in his iconic book The Lore of Running, “God built into us a 32-km racing limit, a limit imposed by inadequate sources of the marathoner’s prime racing fuel- carbohydrates. But we, in our human wisdom, decreed that the standard marathon be raced over 42-km” (596). This is where the mystique of “hitting the wall” comes from- many runners do not fuel properly leading up to and during the race, do not pace properly during the marathon, and, more often than not, a combination of both factors lead to that dreaded “bonk.” The reality is, though, that “hitting the wall” can be minimized with a proper fueling and pacing strategy.
The most common approach to prepare for a marathon is the long-established tradition of carbohydrate loading. The basic premise is that the point of fatigue can be pushed back by “filling the tanks” and packing the muscles with as much glycogen as possible. But, most people do it wrong; it becomes little more than stuffing their faces with as much pasta as they can eat the night before. This can in fact be very detrimental, leading to compromised performances due to sluggishness, bloating, and assorted GI issues. Proper carbohydrate loading is a process that lasts about six days, but with several different approaches.
Two primary approaches to carbohydrate-loading follow similar procedures according to the concept of supercompensation, but with important differences in the details. Both approaches begin about a week before the event with the following steps (Jeukendrup, 130):
- exercise to exhaustion to deplete muscle glycogen levels
- three days of a decreased-carbohydrate diet
- exercise to exhaustion, further depleting muscle glycogen stores
- three days of an increased-carbohydrate diet
The period of low-carb diet “primes” the muscle to accept and store greater amounts of muscle glycogen than a standard diet alone. But, as aforementioned, there are important differences between these two approaches.
The traditional method of carbohydrate loading requires a period of significantly reduced carbohydrate intake leading (25%) to a significantly increased carbohydrate intake (70%); during this time, the athletes engages in very little to no training as part of the taper process. Problems with this method include (Jeukendrup, 130):
- hypoglycemia (low blood sugar)
- GI issues on a high fat/ high protein diet
- poor recovery
- mood disturbances
- tenseness during the period of no training leading up to the event
A more modern approach is to skip the period of significantly reduced carbohydrate intake and maintain a moderate intake (50%), but then to also increase carbnohydrate intake, using a progressive taper in the week leading up to the race or event. This approach proves nearly as beneficial as the traditional method, but with few of the downsides of the low-carbohydrate period (Jeukendrup, 130):
- hypoglycemia is avoided
- GI issues from high fat/ high protein intake are avoided
- recovery is enhanced
- mood levels are maintained
- taper includes training to help athlete relax
These approaches focus on optimizing muscle glycogen levels; however, optimizing liver glycogen levels occurs in the hours before an event, such as morning of an event, and is also important to performance. With both periods of carbohydrate-intake, the focus should be on foods with a high Glycemic Index (GI), as they will be more quickly absorbed and processed than moderate- or low-GI foods. High-GI sources include potatoes, pancakes, pretzels, stir-fried vegetables, and Gatorade. Surprisingly, the traditional meal of spaghetti has a low-GI value and may not be the best choice for carbohydrate-loading.
But, Noakes (152) does raise the question of how to best balance optimizing muscle glycogen and liver glycogen and ingesting exogenous carbohydrate to prevent hypocglycemia. He concludes that all three practices play an important role in optimizing endurance performance.
Jeukendrup A, Gleeson M. Sport Nutrition 2 Ed. Champaign, IL: Human Kinetics; 2010.
Noakes T. Lore of Running 4. Ed.Champaign, IL: Human Kinetics; 2003.
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