Timing Is Everything: The Magic Carbohydrate Window BEFORE Exercise

Given the volume of swim, bike and run training for an Ironman Triathlon (10-25 hours per week depending on individual and time of year), nutrition is critical before, during and after a workout in order to ensure optimal performance during a workout as well as set us up for success for the next workout, which may be the same day.

Timing is everything.

The Magic Carbohydrate Window After Exercise

With a plethora of articles and the availability of recovery drinks like Endurox R4 and Recoverite by Hammer Nutrition, it’s generally well known and accepted in the endurance sports community the importance of consuming some type of carbohydrate and protein beverage or meal within the first few hours AFTER exercise (ideally begin consuming within the first 15-30 minutes), as your body is better able to more quickly replenish the carbohydrates used up during exercise as well as enhance recovery through protein synthesis.

Is there a magic window for consuming carbohydrates BEFORE exercise, too?

The Magic Carbohydrate Window Before Exercise

Whenever you eat carbohydrates, the carbohydrates pass through your stomach where they are broken down into simple sugars, which are then absorbed mostly through the lining of your small intestine into your bloodstream. The simple sugar glucose is what your muscles and brain use for fuel. Other simple sugars – such as galactose and fructose from fruit – are processed by the liver for either storage or conversion to the more usable form of glucose.

Whenever you eat carbohydrates, your pancreas notices the increased amount of glucose and releases insulin to prompt the muscles, liver and fat tissues to take the sugar out of the blood stream into storage so that blood glucose levels return to normal. If you were then to start exercising when insulin levels are already high, your muscles will pull even more glucose out of the blood for fuel. Blood sugar levels in the blood may drop (i.e. hypoglycemia), creating a feeling of weakness and negatively impacting performance.

If you eat a high carbohydrate meal a few hours before exercise, you’re fine. The carbohydrates are absorbed by your small intestine, your insulin levels spike and the sugar is stored in your liver, muscles and fat tissues. By the time you start exercising, your insulin and blood sugar levels are back to normal and you’re able to use the stored carbohydrate (i.e. glycogen) as a fuel source.

BUT, if you could consume some carbohydrate just before the start of the competition such that the insulin and blood sugar levels haven’t peaked yet, would the additional carbohydrate in the blood stream improve performance without creating a condition of hypoglycemia?

The Research

Researchers Savvas P. Tokmakidis and Ioannis A. Karamonolis performed a study¹ to find out if consuming glucose (a form of carbohydrate) 15 minutes before a running event would improve time to exhaustion.

In their study, 11 active subjects ran two different trials on a treadmill until exhaustion after having consumed either water with glucose (1 gram of glucose per kilogram of body weight) or water sweetened with aspartame for flavoring but having no carbohydrate (i.e. a placebo). The participants did not know which drink they were being given before each trial. The study was designed to simulate an endurance race where participants maintain a relatively constant pace (60% VO2 max for 5 minutes then 70% VO2 max for 45 minutes) until the end when they pick up the pace (80% VO2 max) until exhaustion.

The researchers had looked at other studies in cycling that tested the timing of carbohydrate intake at different time intervals before exercise from 15 to 30 to 45 to 60 minutes. All the studies indicated that there was no difference in performance for cycling. This current study was different in that it looked at running, which the authors pointed out, uses more muscle mass than cycling and thereby has greater metabolic demands requiring more carbohydrate as a fuel source.

The Results

Eight out of the eleven subjects improved time to exhaustion by an average of 12.8% when they consumed glucose as compared to flavored water 15 minutes before the start of their test.

The authors believe that the increased availability of glucose in the blood stream delayed fatigue by sparing the glucose stored in the muscle (i.e. glycogen). The authors point out an added benefit of reduced discomfort when drinking a liquid carbohydrate source 15 minutes before exercise as compared to during exercise.

The Takeaway

Consuming a liquid carbohydrate like glucose or a gel 15 minutes before an hour plus long running event appears to be a good strategy to postpone fatigue and improve performance.

Based on my own experiences, I would recommend a little less carbohydrate intake (~100 calories or 1 gel) than the study tested.  I would also consider extending the strategy to other endurance events like triathlons and cycling events, but like anything in endurance sports, be sure to practice this nutrition strategy in training and in less important races before using in your key races.

Live strongly and boldly!

David —- David B. Glover, MS, CSCS
Triathlon Coach, Athlete and Writer
Author of Full Time and Sub-Nine: Fitting Iron Distance Training into Every Day Life
Web: enduranceworks.net

¹ Source: Tokmadkidis, Savvas P. and Ioannis A. Karamanolis, “Effects of carbohydrate ingestion 15 min before exercise on endurance running capacity,” Applied Physiology, Nutrition and Metabolism 33 (2008): 441-449.

© 2010 David B. Glover