Laboratory Investigation Using T Testing and Counterbalanced


The current research sought to determine the effect of moderate caffeine dose (6 mg/kg BM) on repeated high-intensity exercise. The study was conducted in a laboratory setting and adopted the repeated-measures, counterbalanced, placebo-controlled investigation in answering the null and alternate hypothesis. Further, six steps were undertaken in coming up with viable results for analysis in which the T Testing was applied in statistical analysis for the two sets of random variables-caffeine and placebo- within the data set. Measurements on Peak power (PP), mean power (MP), and percentage power drop were undertaken after Bout 1, Bout 2, and Bout 3 of high-intensity exercise. Conclusively, the study found out that caffeine ergogenic effects appear to originate from antagonistic links of the central and peripheral nervous system’s adenosine receptors leading to increase of the central drive and further reduction of the perceived effort and pain when an individual is undertaking high-intensity exercise. Therefore, the ergogenic effects were seen as the reason for the significant increase in Rating of Perceived Exertion (RPE), heart rate, blood lactate, and blood glucose.


Caffeine is a well-known performance-enhancing supplement that has been under active research since the onset of the 1970s. The stimulant is ergogenic and used in close to every exercise and sporting instance (Spriet 2014, 176). Though caffeine contains no nutritional value, it is a globally consumed supplement in various social and sporting settings (de Mejja et al. 2014, 489). Most of the past research examined the impacts of moderate to high caffeine doses (between 5 to 13 milligrams/kilogram body mass) on sports and exercises. The stimulant was in 2004 scrapped off the restricted list of the World Anti-Doping Agency. Argumentatively, moderate to high caffeine doses ingested before and during workouts increase endurance performance with raised heart rates, blood catecholamine, free fatty acid, lactate, and higher glycerol levels in most subjects (Del Coso et al. 2012, 21).


Caffeine functions within the body in a plethora of aspects in performance enhancement (Temple et al. 2017, 80). Therefore, the current research sought to investigate the effects of a moderate caffeine dose on repeated high-intensity exercises. The reason behind it is that such high-intensity short term exercise has in the past not received as much attention as other sports or exercise protocols (Irwin et al. 2011, 512). Moreover, the research sought to assess two learning outcomes. First, to appreciate the use of exercise testing in determining health, fitness, nutritional requirements and intervention’s physiological impacts. Secondly, have a critical comprehension of the composition and use of sports foods, supplements, and ergogenic aids, and their efficacy in performance effect performance. Hence, the null (H0) hypothesis holds that moderate caffeine dose on repeated exercise does not alter heart rate, lactate, Rating of Perceived Exertion (RPE), and body glucose levels. The Alternate (Ha) hypothesis holds that moderate caffeine dose on repeated high-intensity exercise increases the RPE, heart rate, lactate, and body glucose.


The research involved 21 participants (6 males and 15 females) between the ages of 20 and 44. A counter-balanced and placebo-controlled investigation were undertaken for the study. Further, the study applied the repeated measures research design; whereby, the participants took part in each part of the independent variable testing and measurement. Hence, each condition of the testing included the same number of participants. The measured mean weight and height of the participants were 66.74 kgs and 162.98 cm, respectively. Additionally, the research was undertaken in six steps in which the first step involved the recruitment of the participants. Soon after, the consent to participate, and a health questionnaire were completed before any testing was undertaken. The second step required that the participants consume a placebo solution and a test solution, completed within a 2-week gap. The placebo contained 250 milliliters (ml) of water and sugar-free juice (200 ml water and 50 ml juice). The test solution constituted of 6 mg/kg Body Mass (BM) of caffeine added to the 250 ml solution mentioned previously. Following the drink consumption, the participants were to wait for 30 minutes before completion of the test.

The postprandial period in the third step generally constituted measurement of height, weight, heart rate, and baseline blood sample for lactate and glucose measurement. In step 4, a complete exercise bike was set up with added weight to the basket (7% Body Mass and 7.5% BM for females and males, respectively). The participants rested for 25 mins, after which they were ready for the test. The actual testing commenced in the second last step, which involved six seconds of maximal sprinting, followed by 30 seconds of active rest- the cycle was repeated thrice. Three measurements were undertaken; (1) The peak power (power of the actual pulse), (2) Mean power (W & W/kg BM), and (3) the percentage Power Drop. Moreover, the heart rate and Rating of Perceived Exertion (RPE) were measured at the end of every 6 seconds. The last step encompassed blood lactate and glucose collection once again, following the end of the 2 minutes cool down on the bicycle. The T Testing (hypothesis testing) was used in statistical analysis for the two sets of random variables (caffeine and placebo) within the data set.

sets sets

The results revealed that the heart rate kept increasing for both caffeine and placebo after the six seconds of Bout 1 to Bout 2 to Bout 3. However, for some participants, such as participants 4, 14, and 21, the heart rate fluctuated from Bout 1 to Bout 3 and did not relatively increase in the caffeine variable. Further, in the placebo variable for the 21 participants, the figures somewhat rose for Bout 1 to Bout 3, each higher than the preceding as can be witnessed in Table 1 below.


The RPE measurements reveal a relative increase for all the 21 participants all the three Bouts in both caffeine and placebo. Notably, for some participants, such as participant 2, the measurement for caffeine and placebo RPE for Bout 2 and Bout 3 did not change but maintained on 17 and 13, respectively. Further details on RPE measurement on variable one and variable two are expressed below in Table 2.


Comparatively, blood lactate in the post-testing following the 2 minutes of cool down on the bike was higher in caffeine and placebo than in pre-testing. The Biosen C-line was applied for the participants’ blood analysis of the lactate. Further, different glucose measurement results revealed an increase in blood glucose in the post-testing after the exercise compared to before the high-intensity training was conducted. However, for some participants, such as participants 5 and 10, the glucose levels in both caffeine and placebo variables decreased significantly.

The highest peak power (PP) in Bout 1 from all the participants was displayed by participant 21 at 15.44 W/kg, while the lowest was displayed by participant 3 at 7.46 W/kg. Additionally, participant 17 showed the highest Mean Power (MP), standing at 13.71 W/kg, while participant 3 further just like the PP, revealed the lowest MP at 7.02 W/kg. The third recorded measurement entailing the percentage power drop had both participant 10 and 21 with the highest slide at 30% and participant 9 with the least percentage power at 13%, as detailed in Table 3 below.


In Bout 2, participant 21 showed the highest PP at 15.28 W/kg, while participant 3 revealed the lowest at 7.97 W/kg. Results show participant 21 had the highest MP at 12.68 W/kg in Bout 2, while participant 3 showed the lowest at 6.60 W/kg. For Bout 3, 14.09 W/kg was the most increased PP from participant 17 while 6.70 W/kg the lowest as showed by participant 4. Participant 21 scored the highest MP at 12.36 W/kg. Averagely, most of the figures for MP were between 7 and 11 W/kg, as illustrated further in Table 4.


As earlier mentioned, it is well established that moderate caffeine doses ingested 30 minutes before high-intensity exercise tend to raise endurance performance in laboratory testing and field settings (Astorino & Roberson 2010, 259). As the results have indicated, the doses lead to increased RPE, heart rate, glucose, lactate, and glucose in the body. Further, caffeine is ergogenic in different forms in high-intensity exercises in which provision of anaerobic energy plays a significant role in performance success (Paton, Lowe & Irvine 2010, 1249). Argumentatively, the caffeine ergogenic effects increase the central drive and further reducing the effort perception and pain when an individual is undertaking high-intensity exercise. Therefore, the aspect explains why the RPE, heart rate, and lactate significantly rose from Bout 1 to Bout 3. However, one element that remains unclear is whether the correlation between genetic polymorphisms and caffeine metabolism or adenosine receptor density could explain the inter-individual variability witnessed in the ergogenic response in caffeine administration (Stuart et al. 2005, 1998).

However, contrary to the present study, past studies suggest that caffeine ingestion reduces RPE and pain perception. According to Duncan et al. (2013, 395), 4-10 mg/kg ingested 30-90 minutes prior to undertaking exercises reduces obtained RPE during submaximal exercise versus placebo. Nevertheless, the current and past studies affirm that muscle pain perception and delaying onset fatigue are significantly lower in the caffeine condition, irrespective of the type of undertaken exercise (Del Coso et al. 2012, 21). Multiple mechanisms are responsible for the reduction of muscle pain and delay of onset fatigue. Hence, the stimulant blocks the inhibitory elements of endogenous adenosine, resulting in maximal behavioral aspects linked to the release of dopamine, glutamate, and norepinephrine (Smith et al. 2010, 7).

Further research findings assert that caffeine significantly elevated the peak power, mean power but translated to significant percentage power drop which then translated to a significant increase in blood lactate as every trial progressed. According to Paton, Lowe, and Irvine (2010, 1248), previous studies reported no impact of caffeine on PP or MP output; however, the current research suggests that muscle force-velocity links are optimized at top torque factors. Given the significant torque values in the present study, the past studies used torque factors that failed to give a chance for the expression of Wmax (Duncan et al. 2013, 396). Argumentatively, caffeine supplementation's ergogenic influence is considered as arising from the motor unit firing rates and suppression of pain- as was previously mentioned (Livia de Souza et al. 215).

Though it was challenging to identify the reasons behind significant effects on peak power output observed in the research, there was a viable trend towards an impact as the duration of the protocol rose. Thus, it appears most likely that at low torque factors, when the velocity in cycling primarily determines the peak power output, caffeine's benefits on the neural drive might be overweighed by the participants' inability to maximize cycling cadence arising from motor control challenges. However, with increasing resistive torque towards an optimal muscle force-velocity link, the study's participants can meet the demands of coordination of the task and the stimulant effects on the neural drive (Astorino & Roberson 2010, 265).

The present research results have affirmed significant impacts of moderate caffeine supplementation on RPE, heart rate, blood lactate, blood glucose, peak power, mean power, and percentage power drop. Though the results were undertaken in a laboratory setup, the impacts of caffeine on sprinting performance by athletes were realized only under specified conditions such as the lab setting. Therefore, the fact that skilled athletes in running and spring cycling devise strategies that similarly serve in optimizing power output supports a potential benefit of moderate caffeine ingestion on sprinting performance outside the laboratory setting. However, future research is necessary to confirm the significant effects of caffeine on high-intensity exercise under other conditions such as performance depending on the time of day and performance in a state of sleep deprivation.

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Astorino, T.A. and Roberson, D.W., 2010. Efficacy of acute caffeine ingestion for short-term high-intensity exercise performance: a systematic review. The Journal of Strength & Conditioning Research, 24(1), pp.257-265.

de Mejia, Elvira Gonzalez, and Marco Vinicio Ramirez-Mares. "Impact of caffeine and coffee on our health." Trends in Endocrinology & Metabolism 25.10 (2014): 489-492.

Del Coso, J., Salinero, J.J., González-Millán, C., Abián-Vicén, J. and Pérez-González, B., 2012. Dose response effects of a caffeine-containing energy drink on muscle performance: a repeated measures design. Journal of the International Society of Sports Nutrition, 9(1), p.21.

Duncan, M.J., Stanley, M., Parkhouse, N., Cook, K. and Smith, M., 2013. Acute caffeine ingestion enhances strength performance and reduces perceived exertion and muscle pain perception during resistance exercise. European journal of sport science, 13(4), pp.392-399.

Irwin, C., Desbrow, B., Ellis, A., O'Keeffe, B., Grant, G. and Leveritt, M., 2011. Caffeine withdrawal and high-intensity endurance cycling performance. Journal of sports sciences, 29(5), pp.509-515.

Gonçalves, Lívia de Souza, et al. "Dispelling the myth that habitual caffeine consumption influences the performance response to acute caffeine supplementation." Journal of applied physiology 123.1 (2017): 213-220.

Paton, C.D., Lowe, T. and Irvine, A., 2010. Caffeinated chewing gum increases repeated sprint performance and augments increases in testosterone in competitive cyclists. European journal of applied physiology, 110(6), pp.1243-1250.

Smith, A.E., Fukuda, D.H., Kendall, K.L. and Stout, J.R., 2010. The effects of a pre-workout supplement containing caffeine, creatine, and amino acids during three weeks of high-intensity exercise on aerobic and anaerobic performance. Journal of the International Society of Sports Nutrition, 7(1), pp.1-11.

Spriet, L.L., 2014. Exercise and sport performance with low doses of caffeine. Sports medicine, 44(2), pp.175-184.

Stuart, G.R., Hopkins, W.G., Cook, C.H.R.I.S.T.I.A.N. and Cairns, S.P., 2005. Multiple effects of caffeine on simulated high-intensity team-sport performance. Medicine and science in sports and exercise, 37(11), p.1998.

Temple, Jennifer L., et al. "The safety of ingested caffeine: a comprehensive review." Frontiers in psychiatry 8 (2017): 80.

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