The Impact Of Carbohydrate Feeding On Exercise Endurance

The hazards of blood specifically and to a lesser extent urine and saliva are:

(a) Diseases caused by contact with blood-borne viruses such as Human Immunodeficiency Virus 1 & 2 (HIV 1 & 2), Hepatitis Viruses (e.g. Hepatitis B & C), Cytomeglovirus, Epstein-Barr viruses and other unknown viruses.

(b) Infection from an exposed person without sign or symptoms of disease.

(c) Microbiological infections from a whole spectrum of infection agents.

Carbohydrate Consumption

The improvement of exercise activity found association with carbohydrate consumption in 1980s, as carbohydrate was recognized as the ultimate source of energy over the years. This paved way to the concept of carbohydrate feeding which produces ergogenic effects and prolongs the exercise time (Rodriguez et al. 2009). As an individual engages in prolonged and steady exercising, the endogenously stored glycogen and glucose circulating in plasma prove to be the key substrates for providing energy (Jeukendrup 2008).  As these endogenous energy substrates are depleted fatigue caves in. It has been proven that excessive training under conditions of reduced availability of carbohydrate results in increase in oxidative capacity of skeletal muscles (Mul et al. 2015). The molecular basis of the phenomenon, and the involvement of p38 MAPK molecule in altered adaptive responses of skeletal muscles, which occurr during the conditions of restricted carbohydrate intake, has been indicated (Cochran et al. 2010; Röckl et al. 2008). Therefore, ingesting carbohydrates has been known to improve performance and extend duration of exercise capability, by the virtue of enhancing the circulation plasma glucose levels, endogenous glycogen sparing, and increasing rates of exogenous and total carbohydrate oxidation (Temesi et al. 2011). The positive impact of carbohydrate consumption on enhancing the level of physical activity has therefore been a subject of research ever since.

It has been reported that feeding carbohydrate helps in maintaining the blood glucose concentration and oxidation rates. This in turn is observed to increase the exercise capacity with respect to the control group on water. The studies have followed up participants, pushing them to exhaustion levels, and then feeding them ingested or infused carbohydrate or no carbohydrate solution (Carter et al. 2004). Both the ingested and infused carbohydrates enhance the duration of exercise, with respect to the no carbohydrate solution. Amongst infused and ingested, infused solutions have been considered to succeed in maintaining the sufficient blood glucose levels for the participants to engage in extended exercise. This has led to the conclusion that maintaining blood glucose levels is indeed critical for the maintenance of sufficient carbohydrate oxidation rates to extend the exercise capacity (Manore et al. 2009).

Over the time, research has indicated towards females’ tendency to show more reliance on fat instead of carbohydrate oxidation during aerobic exercise performed at same intensity as men. This consideration is essential as the differential requirements could prove to be crucial in designing nutritional recommendations for males and females, in relation to their athletic performance (Tarnopolsky 2000; Jeukendrup 2014). Previous research has shown that carbohydrate feeding during exercise proves to be detrimental in reducing the muscle glycogen utilization in females, however no such effect is seen in males (Gonzalez et al. 2016; Wallis et al. 2006). Another study investigated the metabolic responses of males and females to carbohydrate ingestion during exercise. The study was directed towards the examination of sex related differential metabolic responses, and examined the subjects from both the sexes simultaneously.

Benefits of Carbohydrate Ingestion

The study findings suggested that both sexes showed significant increment in the rates of appearance (Ra) and disappearance (Rd) of glucose when subjected to carbohydrate ingestion as compared to water control. Also, the plasma glucose oxidation contributed significantly to the energy yield upon carbohydrate ingestion in both sexes. The study in totality indicated towards the similarity of metabolic responses in both the sexes, in contradiction with previous results (Wallis et al. 2006). Following the benefits of carbohydrate ingestion, another debate that ensues the concerned phenomenon, is the optimal amount to be ingested for exercise endurance. It has been indicated that ingesting carbohydrates at a rate of 60 g·h−1 allows exogenous carbohydrate oxidation rates to reach maximal levels. Also, well trained athletes exhibit higher capabilities of metabolizing up to 90 g·h−1 of carbohydrate for up to 2.5 hrs, facilitated through multiple carbohydrate ingestions. Simultaneously, small amounts of ingested carbohydrates prove to be efficacious in enhancing shorter and intense workouts (Cermak & van Loon 2013). Smith et al. (2010) in their research indicated towards the relationship between dosage and response between rate of carbohydrate ingestion and enhancement of endurance performance. The group of researchers showed that exogenous carbohydrate oxidation at high rates does not solely enhance the efficacy of performance. A high rate of exogenous delivery of carbohydrates is equally contributing towards performance enhancement. Therefore, in long exercise activities, extending beyond duration of three hours, higher feeding rate complemented by higher oxidation translates into improved performance.

The experimental trials comprised of 14 participants, 7 males and 7 females, recruited from (Provide info). The mean (±SD) baseline characteristics of participants were recorded for the descriptive variables of age, sex, VO2 max, height, waist and hip circumference, as shown in Table 1. The participants comprised of mean age of 25±2.85, with average VO2 max levels of 3.66±1.29 litre/minute, 145.42±63.11cms of height. The average waist circumference was 73.85±7.96, and hip circumference was recorded to be 94.65±3.82. Under certain circumstances all participants could not be involved in all datasets. Due to measurement errors the VO2 max from 1 participant, and waist and hip circumferences from 6 participants could not be recorded. Further all the participants underwent screening procedures, wherein they were required to complete and pass the Physical Activity Readiness Questionnaire for Everyone (PAR-Q+). Besides this, the optimal blood pressure levels must be below 150/90 mm Hg. Also, each participant was required to fill a consent form, and restrained from participating in the experiment if suffering from any health condition.

Sex Related Differential Metabolic Responses to Carbohydrate Ingestion

The study followed double blinded randomized controlled design, wherein the participants visited the laboratory, as the experimental trial was conducted in 2 batches. It was mandatory for the participants to reach the lab in fasted condition, having no food for at least 6 hours prior to the trial. The blood glucose levels were analyzed using ACCU-Check Glucose Analyser. The anthropometric measurements for wait and hip circumference were recorded. The maximal oxygen uptake and power at maximal oxygen uptake was recorded using the incremental cycle ergometer test. The participant underwent the open ended incremental cycle ergometer test till exhaustion. The expired air samples, heart rate, and RPE were measures continuously. The second test involved the constant power test to exhaustion at 90% VO2 max power at maximal oxygen uptake. The oxygen uptake was monitored continuously. The rates of fat and carbohydrate oxidation, and energy expenditure were calculated using the indirect calorimetry method. The participants were allocated the experimental glucose and control water placebo drink in a double blind random manner to exclude any bias or inconsistency in experimental results. The blood glucose levels, heart rate, RPE, and expired gas collection was performed every 15 minutes.

As soon the participant reached the lab the body mass was recorded, and the participant was made to sit quietly for 5 minutes. The baseline resting expired sample was taken to get an estimation of energy expenditure and substrate utilization. The heart rate was also measured. The blood sample was taken by finger prick for estimating blood glucose level. The participant was then allocated 250ml of drink containing either 20 g carbohydrate (high) or less than 2 g carbohydrate (low). Immediately post drink consumption the subject begins to cycle for 90 minutes at 60% of VO_2max power. The participant was given the same drink at an interval for 15 minutes, and expired air samples are taken at 13-15 minutes, 28-30 minutes, 43-45 minutes, 58-60 minutes, 73-75 minutes, and 88-90 minutes during the cycle. The blood glucose samples, heart rate and RPE measurements were taken at 15, 30, 45, 60, 75 and 90 minutes. The workload was immediately increased to 90% of VO_2max power, subjecting the participant to exhaustion. During this part of experiment VO_2, heart rate, and RPE were recorded every minute. A final blood glucose sample, heart rate, was taken at RPE exhaustion.

The data recorded was analyzed, by plotting graphs for glucose concentration, oxygen uptake, energy expenditure, fat oxidation, carbohydrate oxidation, RPE, and heart rate over the trial. The area under the graph for glucose concentration, energy expenditure, fat oxidation and carbohydrate oxidation over the initial 90-minute exercise period was calculated, by utilizing the trapezium rule. Furthermore, the incremental area under the graph for respective variables was recorded, to determine the average changes in value from baseline over the entire observation period.

Optimal Amount of Carbohydrates to be Ingested

The area under curve was calculated to determine the total fat oxidation, carbohydrate oxidation, and energy expenditure. The mean and standard deviation values for other variables of glucose concentration, heart rate, RPE, and time to exhaustion were also calculated. Respiratory exchange ratio: The data analysis showed the difference in respiratory exchange ratio for placebo and experimental groups to be insignificant (p = 0.37). The RER values were however found to decrease with time, as shown in Figure 1. The carbohydrate oxidation data also indicated towards the effect of time on oxidation levels. The rate of oxidation levels for both placebo and experimental groups peaked at 15 minutes, as shown in Figure 2. However, the rate of decline was lower than 15 minutes for all other time periods for both placebo and experimental groups. The lowest oxidation rates were observed at baseline. However, the difference between the two groups was found to be insignificant (t- value = -0.73, p = 0.47).

The fat oxidation data indicated opposite trend in comparison to carbohydrate oxidation rates, as shown in Figure 3. The effect of time on oxidation levels showed a gradual increment for the experimental group consuming high level of glucose. However, for the placebo group the oxidation rates showed a gradual decline at 60 minutes followed by increment in the next 15 minutes. The lowest oxidation rates were observed at baseline. However, the difference between the two groups was found to be insignificant (t value = 0.52, p = 0.60). Energy expenditure, similar to carbohydrate oxidation also showed a sharp increase at 15 minutes, and adopted a constant trend over the following time periods, as shown in Figure 4. The placebo and experimental groups also did not exhibit significant difference in energy expenditure (t= -0.08, p = 0.93).

The blood glucose levels, heart rate, and RPE were also constantly monitored during the experiment. The placebo and the experimental group showed significant difference in the blood glucose plasma levels with t = 4.04, p = 0.001, indicating towards active uptake of consumed glucose for exercising, as shown in Figure 5. However, heart rate and RPE levels showed no difference for carbohydrate ingestion, as shown in Figure 6 and 7 respectively. Heart rate peaked for both placebo and experimental groups at 15 minute interval, which assumed a gradual trend over the rest of the experimental procedure. The RPE scores however at the baseline showed substantial differences for experimental and the placebo group.

Experimental Trials and Design

The present experimental study was primarily aimed at assessing the efficacy of carbohydrate ingestion on exercise metabolism and performance. The metabolic response of the participants towards the ingestion of gradual amounts of carbohydrate was explored. The investigations also aimed towards determination of the strength of association between the metabolic parameters, and their impact on the task outcomes. The gradual increase in the carbohydrate ingestion levels whether low or high, during the non exhaustive phase of exercise resulted in reduction of rate of carbohydrate oxidation and increased rate of fat oxidation levels. The glucose levels increased with respect to increase in dosage, besides increment in the energy expenditure, RPE scores, and heart rate. The effect of time period passage was observed on increasing glucose levels; however no significant interaction effects were evident.

The significant alteration in the metabolic responses towards carbohydrate oxidation evident over the time period of 15 minutes has also been reported by previous research (Newell et al. 2018). This response could be attributed to the glucose dosage, which increased sharply from a fasted baseline to consumption of carbohydrate solutions during the exercise. However, the trend assumed a more gradually pattern over rest of the time intervals. Furthermore, as the blood glucose levels increased for both the placebo and the experimental groups, this could not be necessarily attributed to carbohydrate ingestion. The blood glucose levels may also be altered due to glucose release from liver, hence the present results prove to be highly variable for significant attribution with carbohydrate ingestion. Even low levels of ingested carbohydrate have also been associated with increasing the performance during exercise (Newell et al. 2015).

Additionally, carbohydrate oxidation also did not show any significant differences with respect to highest feeding rates, and differential feeding dosages. The rate of fat oxidation was found to increase which possibly indicates towards higher rate of lipolysis of adipose tissues in exercising humans. This also indicates towards low levels of available carbohydrates to help meet the energy requirements. This finding proves to be contradictory with previous researches which indicate towards blunted fat oxidation when the exercising individual is supplied with additional carbohydrates (Enevoldsen et al. 2004). However, the lack of carbohydrate loading during the trial might have made muscle glycogen available for the purpose of metabolism (Hargreaves et al. 2004). The study results also showed no significant differences between the metabolic parameters for both the placebo and the experimental group. Therefore, the optimal carbohydrate ingestion rate could not be identified, as the energy expenditures for both the groups were found to be the same. It could be concluded that 2 to 20 gms of carbohydrate dosages elicits almost synonymous metabolic responses for both non-exhausting and exhaustive phases of exercise. However, the presented performance measures also involve substantial contributions from preserved endogenous glycogen stores, and adipose tissue.

The present experimental study could gain from future researches expanding upon the methodology and scope proposed here. The research could benefit from utilizing stable isotopes to quantify the glucose movement into and out of the plasma during exercise (Kim et al. 2017). This could help in better monitoring of the carbohydrate consumption rates. Also, an increment in carbohydrate dosage to facilitate significant difference in dosage for both experimental and control groups is recommended. This could help in better exploration of the metabolic advantage of carbohydrate ingestion on enhancement of performance (King et al. 2018). The research on effects of carbohydrate ingestion should also examine the impact of same on metabolism with respect to gender as well. A limitation of the study is shorter duration of exercise, supplied with low feeding rates, and could have resulted in comparable enhancement of performance for both the groups.

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