Glycemic load and pre-workout nutrition -
Study quality was assessed using an adapted version of the validated Downs and Black tool. Potential effect modifiers including exercise duration, pre-exercise meal timing, glycemic load GL , and fitness were assessed using meta-regression. Meals with 0. All test types without CHO ingestion during exercise showed slightly improved performance with LGI, but no significant pooled effects were observed ES: Studies where exogenous CHO was ingested during exercise showed conflicting results ES: No consistent metabolic responses glucose, insulin, lactate, respiratory exchange ratio during exercise were observed with either meal type.
Limitations: There were small numbers of studies within each exercise testing protocol and limited statistical power within studies. Pre-exercise meal timing, GL, meal composition and participant fitness varied across studies, limiting the capacity to assess the influence of these factors on study outcomes.
These results suggest that LGI meal ingested before exercise increases the lipids oxidation to the detriment to carbohydrate oxidation during exercise; however, this effect does not promote the ability to improve endurance running.
Stannard et al. Ten trained cyclists have carried out an exercise on a cycle ergometer with increasing workload to exhaustion the load was increased 50 watts every 3 minutes, starting with a load of 50 watts 65 minutes after ingestion of the HGI meal glucose , of LGI macaroni or placebo artificially sweetened water.
The postprandial glycemic response after ingestion of the HGI meal was significantly higher compared to that obtained in other tests. However, the level of glycemia observed in LGI test to watts of exercise to exhaustion was higher than the HGI test.
It was observed that the concentration of serum lactate in the HGI test from 30 minutes postprandial up to watts of exercise was greater than in the placebo trial, and 45 minutes postprandial to watts was higher compared to the LGI test.
The main finding of this study was that the time of the decrease of glycemia at the beginning of the exercise in the HGI test, coincided with the concentration peak of plasma lactate in this test, also coinciding with the period in which the respiratory exchange ratio was higher compared to the placebo trial.
Therefore, the decrease of glycemia observed during exercise in the HGI test was due to higher uptake and oxidation of glucose by muscle and its lower hepatic release in response to hyperinsulinemia. However, these metabolic responses were not sufficient to reduce exercise performance.
Thus, the strategy of the LGI meal employed by Stannard et al. Febbraio et al. The total amount of carbohydrate in the meals was 1. It was observed that carbohydrate oxidation after consumption of the HGI meal was higher and lipid oxidation, tended to be lower compared to ingestion of the LGI meal.
In addition, muscle glycogen tended to be lower at the end of submaximal exercise in the HGI test. However, there was no difference in performance between the three tests. It should be noted that, although the authors have not shown the content of lipid, protein and fibers offered in the LGI meal, this was composed of muesli oat-based cereal, fruits and nuts.
This kind of cereal certainly contains higher fiber content than the mashed potatoes HGI meal and the amount of carbohydrates available was the same at both meals, indicating that the amount of carbohydrates available differed.
Taking into account that GI of meals was not determined in experimental test, the metabolic and physiological differences obtained in this study comparing the two meals tested, cannot be attributed only to differences in GI between them.
The type of hydration used during exercise after consumption of meals differing in GI can also influence the glycemic response and subsequent performance.
In studies of Kirwan, Demarco et al. In studies of Kirwan et al. On the other hand, Burke et al. Each meal provided 2. In addition to meals and placebo, the individuals consumed 4 and 3. Serum levels of insulin after ingestion of the HGI meal were higher at times 30, 60 and 90 minutes postprandial compared with consumption of the LGI meal.
The glycemic response and insulinemia during exercise was similar between the HGI and LGI meals. It was observed that after consumption of two meals, HGI concentration was suppressed until the beginning of the exercise and whereby 20 minutes of this, was greater on the control test compared to the HGI test.
The time to complete the performance exercise KJ was similar among the three tests. There was no significant difference in respiratory exchange ratio, total carbohydrate oxidation and glucose oxidation ingested in carbohydrate drink between tests.
Burke et al. Under such conditions, athletes can choose the pre-exercise meal according to your habits and preferences. Corroborating the study of Burke, Chen et al. Each meal had 1.
kg -1 body weight and had similar levels of proteins, lipids and calories. It was consumed 2ml kg -1 body weight of carbohydrate drink with 6. The area under the glycemic curve response after ingestion of the HGI meal was four times higher when compared with consumption of LGI meal.
There was no significant difference in the rate of oxidation of carbohydrates and lipids and total carbohydrates and oxidized lipids between tests.
There was also no significant difference in time to complete 21km of running between the two meals. According to these authors, the GI of pre-exercise meal is not as relevant to 21km race of performance when large amount of carbohydrate drink is consumed during exercise. These results suggest that the GI of pre-exercise meal is more important for exercise lasting less than an hour, because after this period is recommended to consume sports drinks that contain carbohydrates in their formulation.
In this condition, the pre-exercise meal could possibly be both the HGI as the LGI, without significant differences in metabolic response during the execution of physical activity.
Although some studies had not observed improvements on performance, it was found a best outcome of metabolic and physiological parameters after the meal consumption of LGI 17—19 , In addition, few studies found no significant differences in these parameters in response to ingestion of meals differing in GI.
These divergent results between studies can be attributed to their methodological differences, such as characteristics of participants gender, age, nutritional status, anthropometric profile and level of training , environmental factors, diet control and exercise in the days preceding the survey, exercise protocol type, duration and intensity , type, shape and amount of carbohydrate offered, composition of the meal, time of ingestion of the meal before exercise, specific metabolic responses to meals, type of hydration offered during exercise water or drink sports and the method for evaluating performance.
All these factors make it difficult to compare the results of these studies. It is noteworthy that despite the results of some studies showed no benefits of ingestion of the LGI meals before exercise in the performance or in metabolic responses during exercise, in this bibliographic review was not observed study in which have found decreased performance in response to consumption of the LGI or MGI meals compared with the ingestion of the HGI meal.
It is also interesting to note that all the studies analyzed in this study were conducted under laboratory conditions. However, the execution of experimental models in field conditions, or even in competition, may also provide important information.
The achievement of research in laboratory has the advantage of controlling the entire chronology of the research since the beginning, the temperature and humidity conditions of the environment. The control of possible variables that may interfere with the experiment is the main advantage of the study in laboratory, since it provides the study of the relation of cause and effect of a particular phenomenon, in a stringent and objective manner.
However, it is necessary to verify the effect of the GI in practical situation, such as conditions of competition, can observe the variability of environmental conditions of temperature, humidity and pressure, the psychological state of the participant, the situation of the route, and other factors that interfere with athlete performance.
The achievement of the study in training environment or competition also allows analysis of the effects of carbohydrate quality in the performance of other modalities, as well as cycling and running. Another suggestion of research, evaluating the effect of the GI on physical performance is to conduct tests involving athletes over the age of 40 or individuals with any pathology that interferes with the glycemic response, for example, diabetes.
The effects of pre-exercise ingestion of meals of high, moderate and low GI on physical performance are still controversial. However, different metabolic responses in relation to the behavior of glycemia and FFA mobilization throughout the exercise resulting from consumption of the HGI or LGI meal were observed consistently.
It is important to emphasize that were not reported cases of reducing performance with the consumption of diets of low or moderate GI before exercise.
Furthermore, methodological differences applied in the studies make the comparison between them difficult. It is necessary to perform better-controlled studies to evaluate the effect of the GI on physical performance.
MMC and JCBM designed the study and assisted the manuscript preparation. MMC was responsible for conducting the study. RCGA and MCGP assisted the design of the study and manuscript preparation. All authors read and approved the final manuscript.
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Supplements and alternate training aside, the lpad way to maximize wnd workout Seamless resupply operations to njtrition fuel your body. Nutritional science muscles require specific nutrients before Glycmic after a workout to build. Keeping your blood sugar level throughout the day is the optimal situation, which is why most serious bodybuilders divide their daily nutrition into six meals, eating a meal every two to three hours, and why understanding the glycemic index GI is key. The GI is a scale that ranks carbohydrates from 0 to according to how quickly they are processed in the body. Foods that contain no carbohydrates are not listed on the glycemic index. The GI rank is not determined by whether the food is a complex or simple carb, although that does factor in. 
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