Hany Salem

Literature review: Caffeine is the most widely used central nervous stimulant and belongs to the methylxanthine class (Nancy, Bieder, 2017). It is classified as a stimulant because it has no nutritional value (Cappelletti et al., 2015). Caffeine is present in tea, sodas, chocolate and in some dietary enhancements (Rutherfurd-Markwick, 2016). It has been noticed that children and adolescents have become the major consumers of these energy drinks. It has been reported that 68% of children and adolescents below the age of 18 consume the available caffeinated energy drinks in the market as compared to only 30% of their adult counterparts above the age of 18 years in the United Kingdom (Zucconi et al., 2013). This high percentage has been enforced by marketing the caffeinated energy drinks as boosters of mental and physical abilities (Zucconi et al., 2013). These caffeinated energy drinks have been widely marketed among children and young people below the age of 18 years and above the age of 11 years. The possible adverse impaction of such caffeinated drinks on the health and wellbeing of children and young people below the age of 18 has to be explored (Visram et al., 2016). Moreover, in 2005, caffeine ingestion has been cleared from the banned substance list of the World Anti-doping Agency (World Anti-Doping Agency, 2015) with the result that caffeine consumption by athletes has been increasing dramatically for its ergogenic effect (McCormack and Hoffman, 2012). There is a large body of research concerning the effect of caffeine ingestion on almost every sport as regard exercise endurance enhancement, muscle strength, and sprints (Glaister et al., 2008; Olcina et al., 2012; Williams et al., 2008). Furthermore, caffeine ingestion has been demonstrated to improve fatigue tolerance (Fett et al, 2018), pain sensation (Caldwell et al., 2017), and time to exhaustion (Skinner et al., 2019). Wilk et al., (2019) proved that caffeine ingestion by resistanttraining 2-years professional athletes enhances movement velocity and increases exercise repetition without tension. Rogers and Dinges (2005) suggested that caffeine ingestion has been associated with increased performance irrespective to the level of exercise intensity. However, the main mechanism of action of caffeine ingestion in the active muscle remains unexplained (Rogers and Dinges, 2005). Recent information shows that caffeine consumption among females is on the ascent. According to James and Watson (2017) despite the fact that caffeine has both positive and negative impacts, there are substantially more beneficial outcomes whenever taken in appropriate proportions. In the recent research article of Glaister (2016) explained that since many studies have observed caffeine-initiated improvement in exercise execution, it is hard to recognize the immediate impacts of caffeine on physiological reactions from those related with the improved performance. According to Brietzke and Cayque (2017), ergogenic impacts of caffeine ingestion have been seen in various cycling exercise modes, and have been related with modifications in evaluations of the rating of perceived exertion (RPE). Paul Foley and Benjamin Henley Williams (2016) explained that consequences show the reason, however frequently unobtrusive, impacts of caffeine on physiological reactions to submaximal exercise. Wallman and Karen (2010) suggested that a moderate dose of caffeine did not improve the performance of cycling embraced in females with a sedentary lifestyle. Supporting this argument Brietzke and Pinheiro (2017) explained in their research that VO2 is not changed but it is increased in response to caffeine consumption in sedentary females. Karen (2010) stated that higher VO2 related to consistent state exercise after caffeine ingestion was likewise reflected by essentially higher expenditure of energy. According to Arhens et al. (2017), the increase in VO2 is due to an increase in stroke volume while taking an account that HR values were not greatly different. It was additionally proposed by Hartley et al. (2004), who described an increase in VO2 as an outcome of a higher stroke volume in females consuming caffeine. Hoseinihaji and Eghbali (2016) recommend that caffeine dosage of 5 mg/kg body mass improve the rating of perceived exertion (RPE) and pain observation in females. However, the portion of 2 mg/kg of body mass does not present any extra improvement in exercise, instead 5 mg/kg improves it much better. Though Arazi (2017) argued that various components may be in charge of decrease RPE in exercise. Caffeine stimulates the sympathetic central nervous system through adenosine receptor antagonism. In this manner, caffeine blocks the inhibitory properties of endogenous adenosine, as a result, the increased practices associated with dopamine, norepinephrine and glutamate discharge (Yoon, et. Al, 2018). The appraisals of the rating of perceived exertion (RPE) can be characterized as relative pressure which happens in the strong, anxious, cardiovascular and pneumonic frameworks during physical movement (Chambers, 2009). As stated by Norian and Eslami (2014), caffeine in higher doses can increase the heart rate during aerobic exercises like cycling in sedentary females but lower doses will reduce the heart rate during low-to-moderate intensity activity. A sedentary way of life is a kind of way of life including almost no physical activity. Living a sedentary lifestyle is turning into a health issue (Owen et al., 2010). A number of chronic conditions are linked with a sedentary lifestyle. Females leading a sedentary lifestyle are prone to develop cardiovascular and pulmonary issues (González, Fuentes and Márquez, 2017). A paper by the Sedentary Behaviour Research Network (2017) suggested that sedentary lifestyle not only affects mental health but can also be the cause of early death. Research explaining the impacts of caffeine on females have yielded conflicting outcomes, proposing that more research is required to decide how caffeine influences females at different life stages (Lyngso et al., 2017). Uptake of caffeine in sedentary females affects the physiology of all the systems of the body mainly including cardiovascular, gastrointestinal, musculoskeletal, reproductive and respiratory systems (McLellan, 2016). Although the accumulating evidence of data have shown that 3.0 mg/kg body weight of caffeine ingestion would enhance exercise performance of football and rugby athletes (Del Coso et al., 2012, 2013), ingestion of the same dose ( 3.0 mg/kg body weight) or higher (0.6 mg/kg body weight) of caffeine was ineffective in enhancing exercise performance in women with average fitness (Ahrens et al., 2007). Compared to placebo, the physiological attributes to caffeine ingestions including RPE, HR, respiratory exchange ratio (RER) has demonstrated no significant changes (Ahrens et al., 2007). Therefore, the impact of caffeine ingestion on the exercise performance of sedentary individuals has been shown to be statistical insignificance (Wallman, Goh and Guelfi, 2010). The same effect of caffeine ingestion on the exercise performance of sedentary females had been noticed in men as well. A double-blind crossover study had been conducted to test the effect of caffeine ingestion on the exercise performance of sedentary men. The results had shown that ingestion of caffeine in a dose of 6.0 mg/kg body weight and exercising for 30 min returned no effect on the exercise performance of sedentary men participants (Laurence, Wallman, and Guelfi, 2012). Therefore, the effect of caffeine ingestion on the exercise performance of sedentary men has returned the same results like that on sedentary women (Ahrens et al., 2007; Wallman, Goh and Guelfi, 2010; Laurence, Wallman and Guelfi, 2012; Tripette et al., 2018). Consequently, the sex difference as an explanation of the impact of caffeine ingestion on the exercise performance of sedentary female participants has been eliminated (Tripette et al., 2018). However, comparing the effect of caffeine ingestion on the exercise performance of sedentary females with placebo returned significant results in terms of increasing the external work, heart rate, energy expenditure, and VO2 (Laurence, Wallman and Guelfi, 2012). Therefore, the promising effect of caffeine as compared to placebo (Laurence, Wallman and Guelfi, 2012) in terms of significant effect on RPE leads to the suggestion that caffeine ingestion would be motivative to sedentary individuals to exercise without effort sensation (Wallman, Goh, and Guelfi, 2010; Laurence, Wallman and Guelfi, 2012). The encouraging effect of caffeine ingestion on sedentary individuals carries promising implications on individuals’ health (Laurence, Wallman and Guelfi, 2012) in terms of encouraging exercise performance for body weight reduction and improvement of physical fitness (Ahrens et al., 2007). The obvious difference between the effect of caffeine ingestion on the exercise performance of sedentary individuals on one side and athletes and active individuals on the other lead to the postulation that active physical exercise would have primed the body to be more responsive to caffeine ingestion than that of sedentary body (Barcelos et al., 2014). Therefore, exercise performance had been noticed to be enhanced with caffeine ingestion in resistance-trained individuals rather than in individuals living a sedentary life (Barcelos et al., 2014; Shearer and Graham, 2014). Trying to explain the dual action of caffeine ingestion on the exercise performance enhancement, Shearer and Graham (2014) reviewed the two opposing effect of caffeine ingestion and energy drinks containing caffeine of both athletic performance and sedentary life. The analysis of the studies showed a reduction of total body glucose disposal by nearly 30% after consumption of caffeine or caffeine-containing energy drinks pointing to the convergence of performance enhancement by caffeine and insulin resistance on the skeletal muscle action (Shearer and Graham, 2014). The synergistic effect between resistance-trained bodies and exercise performance enhancement after caffeine ingestion has been suggested to be due evoking adaptive mechanisms including the presence of small amounts of reactive oxygen species in trained muscle fibers thus facilitating muscle action trigger following stimulant ingestion such as caffeine (Barcelos et al., 2014). Catecholamine release is also suggested as an explanation of the effect of caffeine ingestion on the exercise performance of sedentary individuals (Graham, 2001; Wilk et al., 2019). Graham (2001) suggested that caffeine exerts the effect of enhancement of exercise performance through creating a favorable intracellular ionic environment in well-trained, active muscle, thus boosting the motor power of each motor unit. The exact mechanism of body sensitization to the effect of caffeine ingestion has not been clearly understood, thus further studied are needed (Wallman, Goh, and Guelfi, 2010). The effect of caffeine ingestion on the exercise performance of sedentary individuals has been subject to a great deal of controversy. On one hand, Wallman, Goh, and Guelfi (2010) reported that there is no effect of caffeine ingestion on the exercise performance of sedentary females after strenuous cycling exercise for 10- and 15-minutes duration. Although the participants were instructed to cycle as fast as they could for the same period as athletes and physically active individuals in other studies (Burke, 2008; Talanian and Spriet, 2016) the obtained results showed no statistically significant changes (Wallman, Goh, and Guelfi, 2010). On the other, Doherty and Smith (2005) has conducted a meta-analysis study on the effect of caffeine ingestion on the exercise performance of sedentary population showing that caffeine ingestion succeeded to reduce the RPE by 6%. Considering comparing the effect of caffeine ingestion on the exercise performance of sedentary participants group as well as athletes and physically active participants group, a recent double-blind crossover study reported that caffeine ingestion can reduce the perceived effort and increase exercise capacity during a performance in both groups of patients (Kumar et al., 2019). The discrepancy in the results of caffeine ingestion studies has been explained by Schrader, Panek, and Temple (2013) to be due to the psychological interest of the participants to cycle regularly. Therefore, caffeine has been denied to have any significant benefit in exercise performance enhancement. One more explanation was that the apparent insignificant effect of caffeine ingestion on the exercise performance of sedentary participants would be related to being exercising at intensities less than 75-80% of VO2max (Oda and Shirakawa, 2014; Nédélec et al., 2015). Therefore, it has been recommended by some others to instruct the participants to perform up to exercise intensity ranging from 75-80% for the caffeine ingestion on the exercise performance of sedentary participants could be demonstrated significantly (Doherty et al., 2004; Anderson, LeGrand and McCart, 2018). Another possibility that would explain the discrepancy of the results of caffeine ingestion on the exercise performance of sedentary population is that the sedentary participants were not liking the cycling practice or were not interested in cycling as fast as they can (Wallman, Goh, and Guelfi, 2010). The dose of caffeine ingestion varies between studies thus deepening more the sense of controversy and lack of standardization to compare the studies. A recent comparison study by Chapman and Mickleburgh (2009) that tested the effect of caffeine ingestion among a group of athletes as compared to a group of sedentary female participants supported the notion that VO2 increase after ingestion of caffeine by sedentary individuals (D’Urzo et al., 1990; Powers and Howley, 2012). One more study by Ahrens et al. (2007) has reported a 4% increase in VO2max after 8 minutes walking on a treadmill with moderate intensity. Therefore, caffeine ingestion on the exercise performance of sedentary individuals and the negative results can be attributed to instructing the participants to drink caffeine doses less than 6.0 mg/kg body weight and exercise less than 75% of VO2max (Chapman and Mickleborough, 2009; Larson and Erica, 2018). Furthermore, the previous postulation that caffeine ingestion at a dose of 6.0 mg/kg body weight followed by strenuous exercise using 70% of VO2max for 90 min had no effect on VO2, HR, or RER (Sasaki et al., 1987; Tarnopolsky et al., 1989; Titlow, Ishee and Riggs, 1991) was challenged by the fact that it is the cardiac stroke volume rather than hear rate that was responsible for the increase in VO2 in participant with physiological difference between males and females (Hartley, Lovallo and Whitsett, 2004). Based on the previously cited data, extensive research studies are needed to fill the gap in the research work concerning the effect of caffeine on exercise performance enhancement and resolve the controversy between the studies. The dose of the caffeine should be considered of optimal amount (maximum of 6.0 mg/kg body weight) as well as exercise performance should reach 7580% of VO2. The current study is adjusted to fill the gap in the research and resolve the controversy concerning the effect of caffeine ingestion on exercise performance in sedentary individuals and females are chosen as participants.