Pre-exercise Carbohydrate Intake and the Effect on Performance and Blood Glucose Levels.
There has been a lot of research concerning performance enhancement with early carbohydrate (CHO) supplementation and the effects that pre-exercise supplementation has on blood glucose levels during exercise. Several studies have linked the glycemic index (GI) of CHO to improved performance and time to exhaustion (TTE), but also they have tried to look for a link to hypoglycemia that can occur in some athletes within the first 15 minutes of exercise. Is there a time associated with CHO consumption? Is there a link with the GI of the CHO? The results might be just as vague as the questions. Hypoglycemia in the beginning of exercise is not directly linked to consumption of CHO prior to exercise, but pre-exercise intake of CHO will increase TTE and improve performance capabilities.
Researchers in the past ten plus years have looked at the time of CHO intake, the amount of CHO consumed, and the GI of the CHO consumed to determine the best consumption rate for performance enhancement and lowest risk for exercise induced hypoglycemia. The experimented time frames for pre-exercise consumption are broad and this can produce inconclusive evidence when looking through the research. Time frames range from 2 hours prior to 15 minutes prior to an exercise bout. The dose of 1- 1.5 g/kg of CHO was fairly consistent throughout all of the studies. However, the time of CHO intake will influence the amount of CHO consumed more than time of intake will play a part in determining how successful your exercise bout will be, because even small doses of CHO consumed prior to exercise will positively improve one’s ability to perform endurance and resistance exercises (Karelis, Smith, Passe, & Péronnet., 2010). The evidence for improved performance, or TTE, when endurance training takes place is now common place knowledge. Most studies use endurance athletes when arguing their thesis on the use of CHO prior to exercise for improved performance. In one study examining runners there was an improved TTE of 12.8% in subjects that ingested 1 g/kg 15 min prior to exercise (Tokmakidis, & Karamanolis., 2008). Another study looking at run time found that subjects ran 2.8% faster during a time trail where 1.5 g/kg of either low GI or high GI was consumed 2 hr prior to the run (Wong, Siu, LOK, Chen, Morris, & Lam., 2008).