I am sure that we have all experienced it, at one time or another: cold sweats; bleary-eyes; slowed pace despite a high perceived exertion. A "bonk" occurs when your muscles become depleted of glycogen. In essence, it is a period of low blood sugar.
The physiological impact of bonking is too great to allow it to happen. In the absence of muscle glycogen, the body actually turns on itself breaking down muscle to create glycogen through other means. We never want to see the breakdown of lean muscle mass, that's one of the things that helps us prevent injury.
Bonking can be avoided by fueling yourself properly during training. Never step out the door without at least two gels (or one bar)—more than what you believe is required for your workout. You should have at least one third of your body weight in carbohydrates per hour.
Use a Recovery Drink
A good recovery drink is often overlooked, but can really act as a springboard towards getting the most from your training. Better recovery from one workout will only lead to better performances in the next.
There is no better way to improve the physiological benefit of your workouts and improve your overall recovery than to replenish muscle glycogen immediately following a workout. A good recovery drink should be used following all workouts that are draining, such as track repeats and long runs.
It is often thought that a good recovery drink will be high in protein, in order to promote muscle repair. While protein is a very important component, it is actually more important that the drink contain a high glycemic carbohydrate such as dextrose. If this high glycemic carbohydrate can be coupled with an easily digestible protein, such as whey, then you are really onto something. The most effective recovery drinks will contain a 4:1 carbohydrate to protein ratio. This will help to replenish muscle glycogen and begin the muscle recovery process.
Lose the Loose Baggage
If you were wearing a 10-pound backpack on the morning of your marathon, what would you do before the start? You'd take it off! The same applies to excess weight. Of all the preparations you make, this will have the single largest impact on your race performance.
First, let me repeat the "excess" part as this only applies to athletes carrying extra weight.
It can take years of consistent training to realize the improvements that a 5-pound weight loss can produce. The typical aerobic improvement from year to year, assuming consistent training, is about seven seconds per mile. If you are carrying extra weight, each pound lost is worth about three seconds per mile. Those extra five pounds that you are carrying are worth about 15 seconds/mile. Recognizing that kind of gain would normally take more than two years of training. So, lose nature's backpack and fast forward your development.
Limit Intake of Grains and Refined Sugars
Just because you are training for a marathon does not mean that you are entitled to eat anything that you want. Grains and processed sugars should be avoided, unless you are eating them within an hour of an upcoming workout, during a workout, or within a post-workout window that is equal in length to the workout itself.
This will help to avoid unnecessary spikes in your blood sugar, which can lead to the storage of body fat. In addition, this limited intake of grains and sugars between workouts will leave plenty of room for more nutrient-dense fruits, vegetables and proteins.
Sleep at Least 7.5 Hours Each Night
This is probably one of the most overlooked details by runners. Life is busy: Between work, family, friends, and training, something's gotta give. But it shouldn't be sleep.
Think of sleep as an integral part of your training regimen. Physical training breaks you down. Rest and nutrition build you up. All of the training in the world is useless without proper rest (and nutrition).
If the time that you are devoting to running is habitually taking away from your ability to get 7.5 hours of sleep each night, and you are as time-efficient as possible in the other areas of your life, then perhaps you should devote less time to running. Sure, your volume will be lighter, but your ability to absorb all aspects of your training will be that much better. A well-rested runner is a fast runner.
Race the Distance That You Are Ready For
Give yourself sufficient time to train for a marathon. If you do not have adequate training volume for your event, your performance will suffer significantly due to system failure. You also run the very strong risk of injury and/or an extreme amount of required recovery time following the race. Before signing up, make sure your body is ready to handle the mileage.
You should be able to hit at least two thirds of your critical volume for your race distance. Critical volume for a marathon is run in the two peak training weeks of your plan, which usually fall within six weeks of your race. For a marathon, critical volume should be around 60 miles. Therefore, you should be able to run 60 miles total, over the course of two weeks, at the peak of your training. At a minimum you should be able to run two thirds of this critical distance—which is 40 miles—during the critical period.
If you don't think you can build this this kind of mileage between now and then, you should probably choose a different marathon, or sign up for a shorter race.