Education Essay 代写:Scientific Support Of Caffeine In Sports Physical

Caffeine is a natural substance found in the seeds, plants, or fruits of over 63 plant kinds all over the world. Caffeine is part of a group of compounds well-known as methylxanthines. The most frequently popular sources of caffeine are coffee, tea leaves, cocoa beans, and cola nuts. (Nutrition Guide - Glossary of Nutrition Terms 2010). It is also added to medicines for colds, aspirin and chocolate. (WLR staff, Olsen K., 2009). Additional, caffeine is a pharmacological energetic substance and, depending on the dose, can be a mild central nervous system tonic. Normally is excreted within several hours of ingestion and does not accumulate in the body. (Nutrition Guide - Glossary of Nutrition Terms 2010).

Recommended doses: Adults and children 12 years and over can consume caffeine about 100-200 mg no more than every 3-4 hours. The maximum daily dose is 200-250 mg. Six or less hours before bedtime, timed-release forms, should not be taken. Children under 12 year are not suggested consuming caffeine at all. (Health and Medicine Encyclopedia, 2010). Caldwell in 2006 said that the recommended dosage for any athlete should not exceed 6 mg/kg of body weight, a level that will provide an effective personal performance. Caffeine, may be one of the best-researched dietary supplements, but, research in all areas of caffeine supplementation continues to surface that, caffeine as a supplement, has extensive range physiological effects on the body, that, may or may not result in an improvement in performance. In addition to this, when an athlete consume caffeine supplements, can improve performance but, this is dependent upon a variety of factors as well as, the condition of the athlete, dose of caffeine, form of exercise, mode, intensity, even the length. (Goldstein et al, 2010).

Several studies have investigated the effect of caffeine ingestion on practice and especially in endurance sport. Most researchers used cycling on their researchers and few on other activities such as distance running. Cox et al, (2002), in their study, which was separated in two parts, concluded that caffeine improve performance. Specifically, in their first study, they used 12 male well-trained cyclists who were ingested either 6mg.kg caffeine 1 h pre-exercise, 6 x 1 mg/kg caffeine every 20 min, 2 x 5ml/kg coca cola between 100 and 120 min steady-state and during a time trial, or placebo. They added that, compare with placebo, caffeine in a large dose (6 mg.kg-1) provided 3% performance advantage in TT, independent of timing of intake. In the second part of their study, 8 subjects received 3 x 5 ml/kg of different cola drinks during the last 40 min of SS and TT. They concluded, that, cola drink consumed late in exercise produced 3% performance benefit in TT, compared with cola-flavoured placebo drink. Moreover, in Jenkins, et al, (2008), investigation, the result was that caffeine preparations of 2 and 3 mg/kg improve performance. Kovacs et al, (1998), fill in that addition of relatively small amounts of caffeine (2.1 - 4.5 mg.kg-1), to the carbohydrate-electrolyte solution, improves performance of ~1 hr cycling TT. However, there are and some reports concluding that, no significant effects been of caffeine in performance. Hunter, et al, (2002), using 8 male highly trained cyclist in a case of 90 min cycling at 68% VO2max + TT (~30min) found no difference between trials with respect to entire 100 km or time to finish high-intensity efforts. They concluded, that, caffeine may be without ergogenic benefit, during endurance practice in which, the athlete begins work out with a definite, prearranged goal measured, such as, speed or distance. In another study (Jacobson et al, 2001), the effect of caffeine co-ingested with either carbohydrate or fat was examined. The results of that research, was that, caffeine has no additive effect on substrate utilization or exercise performance.

As far as distance running and caffeine is concerned, a study with seven endurance trained runners were achieved in order to assess the impact of caffeine ingestion on race performance during high-heat stress. Cohen, et al, in that research, concluded, that caffeine is not of ergogenic advantage in endurance races during high-heat stress.

Sustained High Intensity Sports (1-60 min)

Moreover, there are many studies, supporting that caffeine can improve performance of sustained high intensity sports (1-60 min), such as rowing, swimming, running and cycling.

For instance, Anderson et al, (2000), in their research using 8 female well trained rowers, and ingesting them 6mg.kg-1 or 9g.kg-1 pre-exercise, concluded that caffeine improve performance for both doses. Specifically, caffeine enhanced performance in the first 500m rowing after trial 2,000m on a rowing ergometer. In addition, Bruce et al, (2000), in a similar research, using the same doses of caffeine, found the same results using this time 8 male well trained rowers. Furthermore, benefits of caffeine ingestion on sprint performance in trained and untrained were examined by Collomp et al, (1992). Fourteen male and female swimmers tested during a sprint test (2 x 100m); separated by 20 min. Caffeine of 250mg (~4mg.kg-1) was provided to both of them in the first test (1 x 100m) 60 min pre-exercise. Results, showed that, a significant improvement noted in their first test. However, in the second trial (1 x 100m), where, a placebo 'ingested', only trained subjects exhibited significant improvement. After this research, Collomp et al, concluded that specific'' training is required to benefit from the metabolic adaptations induced by caffeine during supramaximal exercise requiring a high anaerobic capacity.

As far as middle distance and distance running is concerned, Bridge and Jones (2006), assessed the effect of caffeine ingestion on 8km run performance using 8 male distance runners ingested with 3mg.kg-1, 60 min pre-exercise. In their results, found that, ingestion of 3mg.kg-1 body mass of caffeine can improve absolute 8km rum performance in an ecologically valid race setting, than, a placebo capsule, or no supplement. Additional, Wiles et al, (1992), used two protocols in order to determine the impact of caffeinated coffee on running speed, respiratory factors, blood lactate and perceived exertion during 1500-m treadmill running. Finally, they also concluded that ingestion of caffeinated coffee could improve the performance of constant high-intensity exercise. Last but no least, Wiles et al, (2006), agreed with the previous researches that found improved performance after caffeine ingestion during short-duration high intensity exercise and specifically in track cycling.

Team and racquet sports

It is extremely difficult, to find evidence in the literature, supporting the benefits of caffeine supplementation, on athletic performance in team sports and racquet sport. The effects of caffeine, are difficult to detect in such sports, and recent studies demonstrate problems in the reliability or validity of protocols. (Burke, M.L., 2008). Many investigations require further consideration, however, there are and some investigations that deserve to be read.

Schneiker et al. (2006), in his study used 10 male team sport athletes, ingesting them 6 mg.kg-1 of, caffeine, 60 min pre - exercise. He examined the effects of acute caffeine ingestion on prolonger intermittent - sprint performance. The study, revealed, that acute caffeine ingestion can significantly improve performance of prolonger, intermittent - sprint ability in competitive, male, team sport athletes.

Moreover, Stuart et al, (2005), ran a survey, in order to examine effects of caffeine in a performance test simulating physical and skill demands of a rugby union match. He also ingested his subjects (9 males/rugby union players), with 6 mg.kg-1 of, caffeine, 70 min pre - exercise. On the one hand, in this research the improvements made, due to the reduction of fatigue that developed throughout the trial, and on the other hand, partly by enhanced performance for some measures from the first circuit of the trial.

Stuart et al, (2005), concluded that caffeine is expected to cause significant enhancement of various aspects of high-intensity team-sport performance.

However, Paton et al, (2001), in his study did not find any statistically significant improvements, of caffeine ingestion on team sports. He investigated, the effect of caffeine ingestion on sprint performance, with a test that simulates repeaters sprints of team sports, using 16 team male athletes (6 mg.kg-1 caffeine, 760 min pre - exercise). Although, the investigation is still under verification, the effect of caffeine ingestion on average sprint performance and fatigue that was observed was insufficient, so, team-sport athletes should not believe caffeine to enhance sprint performance.

Two surveys related to racquet sports and specifically tennis, which will be mentioned below, were investigated the effects of caffeine supplementation, however more surveys with different types of racquet sports should be done to provide more evidence for research in the literature. To begin with, Strecker et al. (2007), in their study examine the effect of caffeine ingestion on Tennis skill performance and hydration status. Ten male collegiate tennis players, were ingested with 3mg.kg-1/BW of caffeine 90 min pre-exercise. The result of this research, demonstrated that, ingestion of caffeine improves tennis skill performance in the later stages of a tennis match play. Furthermore, caffeine may increase tennis success in female because of the improvement of glucose homeostasis at the beginning of work load after rest. (Ferrauti, et al, 1997).

Effects of Caffeine supplementation

On the one hand, caffeine may be useful in terms of athletic performance, but , on the other hand sometimes the over use or misuse can cause problems.

According to Bridge and Jones (2006); Cox et al. (2002); the beneficial effects from caffeine occur at very modest levels of intake (1 - 3 mg/kg-1 body mass, or 70 - 150 mg caffeine). Specifically, Bridge and Jones (2006), in their double blind study, involved 8 male distance runners, which ran an 8 km race 1 h after ingesting a placebo capsule, a caffeine tablet (3mg .kg-1 Body mass) or, no supplement. Finally, they conclude that ingestion of 3mg.kg-1 body mass of caffeine can improve 8km run performance. On the contrary, doses of 6-9 mg.kg-1 and over may be related with side effects, such as nervous, increased heart rate and performance destruction. (Graham and Spriet, 1995).