Essay: Caffeine does not have any effect on improving aerobic capacity

Coffee is a popular and complex compound consisting of substantial amounts of both chlorogenic acid and caffeine (McCusker et al, 2003). Caffeine is a popular dietary supplement from the methylxanthine family, predominantly known for its stimulant properties (SDA, 2011). The caffeine concentration in coffee has recently made the beverage one of much interest to both scientific researchers and athletes; with endurance athletes now exploiting the substance as an ergogenic aid to enhance training intensity and competitive performance (Anseleme et al. 1992; Graham & Spriet, 1991). This may be attributed to the ability of caffeine to bring about numerous physiological responses through the antagonism of the Adenosine Triphosphate (ATP) receptors in the brain, resulting in enhanced adrenaline production; subsequently stimulating energy release and optimising blood flow to major bodily organs, primarily the heart and muscles (Goldstein et al, 2010). This is reflected in an increase in VO2max, which is a major determinant of aerobic capacity. This increase translates to a heightened ability of the body to distribute oxygen and efficiently produce ATP hence prolonging aerobic endurance alongside delaying fatigue (Spriet, L. 2014).
Although there is substantial research available regarding the effects of caffeine consumption on both aerobic and anaerobic performance, little is known about the efficacy of coffee and acute caffeine consumption on aerobic capacity (Higgins et al, 2015). The following study will demonstrate the efficacy of coffee in enhancing aerobic capacity, through a double blinded experiment in which a number of subjects consume 100ml of coffee (~180mg caffeine) and undergo a physical step-test. The use of a step test is most suitable as opposed to time-trial tests used in other studies, due to high reproducibility and appropriateness in replicating endurance sports (Cooney et al, 2013). Subjects will be monitored through collecting and recording pulse rates pre/post treatment and post exercise, hence showcasing the differences in heart rate, if any.
Methods
Subjects are required be daily caffeine consumers, have optimal respiratory health, have consumed food within 2 hours of the practical and not consumed any beverage but water. The experiment was then conducted, as follows:
1. Subjects were instructed to measure and record their resting pulse rate (pre-treatment) at the carotid artery for 30s and doubling it, then record the final number.
2. The subjects were then split into two groups A or B, and allocated to respective stations.
3. In a blind test, the subjects will consume either substance A or B, for group A or B respectively. The beverages contain 6 g of either coffee or decaffeinated coffee dissolved in hot water.
4. The subjects were then dismissed for 1 hour.
5. Subjects were called back to measure and record their post-treatment pulse rates. They then prepared to perform an incremental step test, using a metronome to regulate the speed of the activity.
6. The step test was then conducted; the exercise ran for 5 minutes, with the rate of the stepping increasing every minute from 20 steps/min, 24 steps/min, 28 steps/min, 32 steps/min to 36 steps/min.
7. Immediately on stopping, the pulse rates (post-exercise) of the subjects were measured and recorded.
Results
Summarised results of pre-treatment, post-treatment and post-exercise heart rates, of both caffeinated and decaffeinated groups are shown in Graph 1. The raw data of both treatment groups is given in the Appendix (Table 1).
Graph 1. Heart rates (Bpm) for both caffeinated and decaffeinated subject groups; recorded pre-treatment, post-treatment and post-exercise.
The results in Graph 1 are collated from a total sample size of 106 subjects, 57 in the caffeinated and 49 in decaffeinated group. The results show that there was no significant change in mean pulse rate in both caffeinated and decaffeinated subjects when recorded before and after the treatment was consumed. However, across all treatment groups there was a significant increase in heart rate when recorded post exercise. The mean pulse rate post-exercise of the caffeinated group was slightly lower than that of the decaffeinated group post-exercise. These results are depicted in the statistical statements obtained through a two-way analysis of variance (Extract 1).
Extract 1. Two way Analysis of Variance; statistical statement for results of experiment.
Discussion
The results show that there was no correlation between caffeine consumption and increased heart rate, rather the cause of a greater VO2 max post-exercise was simply due to intense physical activity. As previously stated, there was no significant difference in mean pulse rate between subjects of both caffeinated and decaffeinated groups at all stages of the trial (ANOVA: F(1, 312) = 0.09, p > 0.05), therefore disproving the hypothesis. It should be noted that in the results, the decaffeinated coffee group showed a slightly greater increase in mean pulse rate at post exercise as opposed to the caffeinated group; signifying that caffeine consumption had little effect on VO2 max and hence did not improve aerobic endurance.
Although there is ample research on the effect of high doses of caffeine (>3mg. kg-1) on aerobic performance, little evidence is available on the efficacy of acute caffeine consumption (<3mg. kg-1) on aerobic capacity. Very few sources that utilised low caffeine doses supported the findings of the study. In a similar test, subjects were given a low dose of caffeine (1.5 mg/kg) of caffeine 1 hr prior to completing a physical time trial cycling test and showed no improvement in time trial performance with caffeine (Desbrow et al 2012), hence supporting the results of the study. This similarity may be due to the relatively comparable caffeine dosage that was utilised in both studies as well as the
Considering other available sources, the results presented in this trial contradict the results of the majority of past research. With other researchers depicting an increase in mean pulse rate after consuming acute concentrations of caffeine, and consequently resulting in greater performance. In one time-trial, habitual caffeine-consumer athletes displayed a substantial improvement in performance following ingestion of low dose caffeine 90 minutes prior to exercise (Irwin et al, 2011). One study found that well trained cyclists who were given low doses of caffeine 1hr prior to completing a time-trial test had performance improvements of 4.2% evident in caffeinated groups as opposed to placebo and decaffeinated groups (Desbrow et al, 2012). Furthermore, a meta-analysis of previous studies on the effect of caffeine consumption on aerobic endurance, concluded that three of six studies
Although both trials show an improvement in performance and consequently a positive correlation between caffeine consumption and performance, the difference in results when compared to the original study may be attributed to the numerous factors. The trials of researchers were predominantly time trials, yet the trial used in the initial study was a step test hence better reflecting aerobic endurance as opposed to performance. Furthermore, such differences may also have arisen due to the slightly higher caffeine dosage given to the subjects of other research, as opposed to the 6mg in this trial. Hence, indicating the lack of research in regard to acute consumption of coffee as opposed to high dose pure caffeine on aerobic capacity. Notably, other literatures were based on subjects consuming pure caffeine as opposed to coffee, which may have distorted the effects of the substance on the athlete. This may be attributed to concentrations of chlorogenic acids in coffee which may antagonise the physiological effects of caffeine (Graham et al, 1998). Studies have shown that the presence of chlorogenic acid in coffee may inhibit the full functioning of caffeine due to the properties of the phenolic compound delaying Adenosine Triphosphate receptor binding (Pauli T et al, 2002), as well as causing cardiorespiratory effects such as blunting to heart rate and blood pressure (Tse, S. 1992). Consequently, limiting increases in Vo2 max following coffee consumption and having little effect on improving aerobic capacity.
Conclusively, the results of the study have shown that acute doses of coffee did not alter mean pulse rate and had little variance in comparison to subjects who consumed decaffeinated coffee. These results indicate that caffeine did not have any effect on improving aerobic capacity in subjects as the VO2 max did not increase, inhibiting optimal blood flow and consequently having little effect on prolonging exercise and decreasing fatigue. These results have provided much needed insight into the use of coffee specifically as an ergogenic aid in aerobic capacity, as opposed to concentrated pure caffeine on improving aerobic performance. Although ample research has shown that high doses of caffeine (>3mg. Kg-1) may significantly improve aerobic performance, there is little effect of acute caffeine consumption on aerobic capacity.