Introduction
Caffeine is a naturally occurring stimulant sourced widely in day-to-day life in substances such as tea, coffee, energy drinks and kola nut (Persad 2011). Due to the prevalence of caffeine consumption, many studies have been conducted to investigate the impact of caffeine on the body (Persad 2011), in particular, its effects on aerobic performance. From the research, the effects of caffeine are determined by many factors such as fitness level, age, gender and daily caffeine consumption (McLellan & Bell 2004). In the context of sport, caffeine is recognised as an ergogenic aid which enhances performance and alters physiological and psychological responses during exercise (Brietzke et al. 2017; Burke 2008) by increasing aerobic endurance and fat and carbohydrate metabolism (Graham et al. 2008). Aerobic capacity, assessed by determining the maximal oxygen uptake (VO2max), describes the efficacy of the body to distribute oxygen to the muscles (School of Life and Environmental Sciences Biology Manual 2018). This in turn increases heart rate and hence stroke volume and cardiac output (School of Life and Environmental Sciences Biology Manual 2018). During exercise, as the heart pumps more blood, greater quantities of oxygen is delivered throughout the body and hence oxygen delivery to the muscles is enhanced, preventing fatigue and prolonging aerobic endurance (School of Life and Environmental Sciences Biology Manual 2018). Conversely, neither a 3mg nor 6mg/kg dose of caffeine altered physiological responses of 19-28-year-old women of average fitness level, not habituated to caffeine while they performed an aerobic dance bench-stepping routine (Ahrens et al. 2007).
Hence, the research question was defined as “Does acute caffeine consumption enhance aerobic performance?”
The study was conducted by dividing the First Year University of Sydney Human Biology students into Stream A and Stream B. Selected Stream B volunteers were further separated into groups A being caffeinated (n = 57) and B being decaffeinated (n = 49). The subjects consumed the appropriate substance (either 180mg caffeine or decaffeinated coffee) for their allocated treatment group and were given an hour break to maximise caffeine absorption into the bloodstream before they participated in a moderately intense Harvard step-test for five minutes. Immediately after, the pulse and heart rates were obtained (School of Life and Environmental Sciences 2018). Therefore, the aim of the investigation was to observe the effect of caffeine on aerobic performance whereby any changes in pulse and respiratory rates of the test subjects before and after exercise would be utilised as a guide of aerobic performance.
Hypothesis
Null Hypothesis: There is no significant difference between the mean change of pulse and respiration rates after exercise between either the caffeine and decaffeinated groups.
Hypothesis: Caffeine consumption increases aerobic performance by increasing heart rate or VO2max. There is significant difference between the mean change of pulse and respiration rates after exercise between either the caffeine and decaffeinated groups.
Methods
Refer to the School of Life and Environmental Sciences Biology Manual (2018).
Results
In this experiment, Group A participants took substance A which is caffeinated and Group B participants took substance B that did not contain caffeine. In group A, 57 participants were involved and in group B, 49 participants were involved. The mean change in pulse rate for caffeinated group A was 46.4 (derived from subtracting 124.8 and 78.4) beats per minute and the mean change in pulse rate for decaffeinated group B was 48.4 (derived from subtracting 127.7 and 79.3) beats per minute. The final exercise pulse rate (post-exercise) standard error results are 3.6 and 4.0 respectively for caffeinated and decaffeinated groups.
Figures and tables
Figure 1. Stream B – mean pulse rate changes for decaffeinated and caffeinated groups after exercise
There was no significant difference in the mean pulse rate between subjects who consumed caffeinated coffee and those who consumed decaffeinated coffee (ANOVA: F(1, 312) = 1.01, p > 0.05). Across all coffee treatment groups, the mean pulse rate at pre-treatment was significantly different to that at post-exercise (ANOVA: F(2, 312) = 211.50, p < 0.0001; Tukey’s multiple comparisons: p < 0.0001) and the mean pulse rate at post-treatment was significantly different to that at post-exercise (ANOVA: F(2, 312) = 211.50, p < 0.0001; Tukey’s multiple comparisons: p < 0.0001).
Discussion
The experiment did not show a distinct difference in the results between the decaffeinated and caffeinated groups. The range of mean pulse rate of the decaffeinated group was 79.3 beats per minute whereas the caffeinated group was 78.4 per minute which contradicts the hypothesis in that the decaffeinated group displays a higher mean pulse and respiratory rate when compared with the decaffeinated group. However, according to the standard error values of the final exercise pulse rates (post-exercise), the range of data overlap therefore they are not significantly different. Thus, the effect of caffeine on pulse and respiration rate is very low or has no effect which verifies the null hypothesis. The null hypothesis was further confirmed by the t-test results where p > 0.05 in both respiration and pulse rate between the two groups. Therefore, the results obtained contradict the hypothesis which renders the experiment neither reliable nor valid.
Many factors support the fact that the results of the experiment were inaccurate. The investigation was carried out in a double blind randomised trial manner whereby both the investigators and participants did not know which groups consumed the caffeinated and decaffeinated drinks respectively. Hence, it can be assumed that the decaffeinated group had a placebo effect on their heart and breath rate. However, in several cases, chief errors at the forefront of the experiment include the participant sample sizes in that the respiration rate ranges in both the decaffeinated and caffeinated groups showed negative results. This sheds light on the fact that participants had marked decreases in respiration rate. As both the pulse and respiration rates were measured by the participants of the experiment themselves, human errors could therefore be introduced when measuring the participants’ heart beats and breaths per minute. Standardised controls not undertaken prior to the experiment. The reliability of the experiment can be improved by repeating the experiment several more times and setting up same-gender athletes with same fitness levels who have trained under the same conditions from the same sporting teams to increase the reproducibility and thus reliability of the data collected and hence reduce the variance. Furthermore, controlling the quality of food and fluids ingested before the experiment in addition to accounting for the individual time it takes for caffeine to take its effect on the body and metabolise would increase the validity of the experiment and reduce any variance.
Conclusion
The conclusion derived from the data is that caffeine consumption has no effect on the pulse and respiration rate which refutes the hypothesis. There are many variables that have not been adequately taken account for and thereby controlled. It is therefore recommended that factors such as prior food and caffeine consumption, fitness level and gender are to be controlled in order to obtain relevant, reliable, valid and accurate results in the future.
Appendix
Figure 2. Stream B – compiled statistical results