Cho_Consumption_During_Exercise

The outcome of carbohydrate feeding during exercise on exercise capacity. Carbohydrate (CHO) is a source of energy for the body and it is broken down into glucose by amylase; it can be stored in two ways, as muscle glycogen or liver glycogen. It is the main source of energy when people participate in moderate-high-intensity exercise which is 70% + of heart rate reserve. We aimed to discover the effect of CHO consumption immediately before and during exercise on subjects exercise capacity and metabolism rates. Maughan and Burke (2002) state that prolonged cycling is related to depletion of glycogen in the quadriceps when performed at around 70% of heart rate reserve. This relates to their assumption that the depletion of glycogen in the quadriceps is linked to the exhaustion capacity of athletes. Maughan and Burke (2002) also found that research studies have shown a benefit of CHO intake during extended periods of exercise at high intensity, in cycling however the availability of CHO is not seen as the limiting factor to performance and they believe further research should be done to confirm the effects. The ingestion of CHO during a period of prolonged exercise is shown to increase exercise capacity and delay fatigue most of the time. Although there are studies that show no effect of CHO feeding for high-intensity exercise such as Clark, Hopkins, Hawley and Burke (2000), and Tsintzas et al who found a reduced muscle glycogen breakdown in cyclist with type I muscle fibers after 60minutes compared to type II muscle fibers which were unaffected. Green (1991) found that the depletion of endogenous glycogen inhibits an athlete’s ability to sustain prolonged exercise; he also states that the mechanisms of glycogen depletion to fatigue are still hard to define. Where-as Maughan and Burke (2002) state if depleted endogenous stores can be substituted with exogenous CHO then when glycogen stores limits endurance, exercise capacity should be increased. Jeukendrup (2004) believed a mechanism that may improve by feeding CHO during exercise was the maintenance of CHO oxidation at a high level. The type and amount of CHO, feeding intervals and exercise intensity have all been researched to find the most effective method of maintaining CHO oxidation. However Coyle et al (1986) have shown that CHO oxidation dropped after 1.5hours with the placebo however oxidation rates were sustained with CHO feeding. Coggan and Coyle showed that liver glycogen is spared when CHO is fed during exercise; this isn’t the case for muscle glycogen which is depleted at the same rate during moderate-intensity exercise whether CHO is fed or not. Although if CHO isn’t fed during prolonged exercise then as liver glycogen stores decrease so do blood glucose stores. When this depletion occurred CHO oxidation levels fall and there can be an early onset of fatigue. They also suggested that even when blood glucose concentration is maintained during exercise there will come a point that the subject will need to stop, which leads them to believe there is more than the delivery of fuel to muscles contributing to fatigue (Powers & Howley, 2009). Method: The participants in this study were university students from sports science degrees, and participated voluntarily in the laboratory experiment. There were ten volunteers who took part in the study aged between 18-22 years; four of these participants were female with the remaining six being male. The participants were required to fill out a health screening questionnaire and give informed consent prior to undertaking the experiment in week 1. The experimental design was repeated measures this was so there were no individual differences between the two sets of results; the experiment was conducted as a double-blind placebo controlled cross-over trial. A carbohydrate-free drink and a carbohydrate drink of a 6% concentration were used in this experiment. The Experimental Procedure: Once the subjects had completed the health screen questionnaire and provided their informed consent, their height and body mass were taken before a ten minute rest period that provided resting baseline measurements. The resting baseline measurements include heart rate, blood glucose concentration, blood lactate concentration and a one minute sample of expired air. Whilst the subjects were resting the Servomex was calibrated to enable the gas readings taken during the experiment to be accurate. Once this was done the Harvard dry gas meter was used to empty the Douglas bags ready to be used for the air samples. The subjects were required to adjust the seat and handlebars of the Monark cycle ergometer before performing a 5 minute warm up at 70w; the settings for the bike were recorded to enable the bike to be set up the same the following week. Whilst the subjects warmed up the experimenters calculated 60% of their heart rate reserve in preparation for the main experiment. After warming up the subjects were required to drink 500ml of either the CHO solution or the CHO-free placebo and they then proceeded to start exercising immediately. The subjects exercised for 60minutes, maintaining a fixed pedal cadence of around 70rpm and at 60% of heart rate reserve. After the initial consumption of the test drink subjects were required to consume another 100ml of drink at ten minute intervals from 10 to 60 minutes, also at these intervals Heart rate and Rate of perceived exertion (RPE) were recorded. Blood samples were taken by pricking the subjects finger at 15 minute intervals starting at 15 minutes through to 60minutes; these were analysed for concentrations of blood glucose and lactate. Expired air was collected for 1 minute at the following time periods; 13-14, 28-29, 43-44 and 58-59 minutes. Once the subjects reached 60 minutes the workload was increased by 50% and they were required to exercise until volitional exhaustion. Subjects were required to indicate when they could not continue exercising for much more than a minute; here a final sample of expired air was collected before they stopped cycling. When the subjects reached volitional exhaustion the time was recorded in minutes and seconds and a final blood sample was taken along with Heart rate and RPE readings. Week 2 was conducted in the same way as week 1; however the subjects received a different test drink to the one they consumed in week 1. Data Analysis: The data was downloaded from the university’s online workspace in the form of an excel spreadsheet. It was then transferred into SPSS- a statistical analysis programme to run the relevant analysis to check the collected date for any parametric assumptions. The performance time between the two tests was compared by running a paired samples t-test, this was done in SPSS by clicking analyse, compare means, paired-samples t-test. Once the dialogue box opened we moved the data to be analysed over before clicking ok to produce the t-test results. The paired samples t-test was run because there was only one observation for each nominal piece of data. When there are multiple measurements from the experiment of each participant when consuming a carbohydrate-free or a carbohydrate solution a two-way repeated ANOVA should be used. The two-way within group repeated ANOVA was used to compare differences in blood glucose, blood lactate, heart rate, respiratory exchange ratio and RPE across the time intervals between the different trials. Again this was done in SPSS and we started by clicking analyse, general linear model then repeated measures. Once the dialogue box had opened again we entered the within-subject factors and the number of levels that each variable had, for example trials always had two levels. We then pressed define to move the variables we wanted to analyse over to the within-subject variables column; once this was done we clicked on plots and moved trials over to separate lines and the independent variable was then moved to the horizontal axis to enable graphs to be plotted once continue has been pressed. Once the ANOVA had been run the output allowed us to test the sphericity of the results and whether to interpret them using sphericity assumed or greenhouse-geisser. This was done by looking at the sig. value in Mauchly’s Test of Spehericity and if p< 0.05 then the assumption is violated. Here we moved onto the next table and analysed the date using greenhouse-geisser and if p > 0.05 then there was no significant difference. If the assumption wasn’t violated we analysed the data using Sphericity Assumed. Results: Table 1: Exhaustion times for CHO and Placebo trial. |Subject |CHO exhaustion time (minutes) |Placebo exhaustion time (minutes) | |1 |10.56 |7.47 | |2 |9.23 |8.45 | |3 |10.15 |9.26 | |4 |10.25 |8.46 | |5 |11.38 |8.12 | |6 |17.25 |12.01 | |7 |8.53 |5.47 | |8 |9.5 |7.0 | |9 |11.0 |8.03 | |10 |13.45 |7.01 | |MEAN |11.13 |8.128 | The table shows that all of our subject’s exhaustion time was extended when participating in the CHO trial. Subjects 6 and 10 showed the greatest increase in exhaustion time between the two trials retrospectively lasting 5.24 and 6.44 minutes longer. A paired samples t-test was conducted to compare the exhaustion time of subjects in a CHO and placebo trial. The CHO trials mean exhaustion time was longer and there is a strong positive correlation of 0.720 between exhaustion time in the CHO and placebo trial. T= 5.380 showing the extent of difference between the two means, df= 9 and finally there is a significant difference as p=0.05, we used sphericity assumed and found a significant difference; df= 5, f= 8.049 and p=