Caffeine improved performance

Caffeine improves performance on tests of semantic memory, free recall, and recognition memory (Smith et al. 1994 Warburton 1995). However, the effects are both dose and task dependent. In some studies, higher doses produced greater improvement, while in others subjects receiving caffeine performed slightly worse than placebo (Loke 1988 ... 

Caffeine has non-specific stimulant effects on attention and alertness, in the sense that it affects multiple capacities. Furthermore, imlike many illegal drugs it has a self-limiting effect in the sense that users do not desire to increase the amount they drink the more they drink. In fact, at low doses increases in caffeine improve performance but at high doses caffeine actually impairs performance. At high doses users tend to feel anxiety and tension which cause them to abstain from further use (Bonnefond et al., 2004 Smith, 2002). This self-limiting nature also means that caffeine has a very low addictive potential (Lorist and Tops, 2003). 

McLellan, T. M., Bell, D. G., Kamimori, G. H. (2004). Caffeine improves physical performance during 24 h of active wakefulness. Aviat. Space Environ. Med. 75 (8), 666-72. 

Caffeine improves psychomotor performance. For example, improvements are seen in manual dexterity (Bernstein et al. 1994). Enhancement of psychomotor performance is most evident when subjects are fatigued (Snyder and Sklar 1984). 

Following 500 mg of caffeine and after tea ( 10 g of yellow China and black East Indian tea, allowed to infuse for 5 min), improved performance was observed in a number of areas an increase in the number of additions in the... 

A frequently used test to assess the effect of psychostimulants is the CPT. Methylphenidate at doses of around 0.3mg/kg usually improves performance, Le. reduces the number of errors, on the CPT whereas the effects of d-amphetamine (at doses between 5 and 20 mg) and pemoline (10 60mg) appear to be less reliable (Riccio et al., 2001). The stimulating effect of caffeine in various areas of performance is of shorter duration than that of... 

Although the effects of caffeine on some aspects of performance may be difficult to establish, the impact of this compound on tasks requiring vigilance or sustained attention is clearer. Lieberman et al. (110) evaluated the impact of 32-, 64-, 128-, and 256-mg doses of caffeine on a four-choice visual reaction time test (10 min), a continuous-performance task (variable duration), and the Wilkinson auditory vigilance test (1 hr). Results indicated that every dose of caffeine improved four-... 

Although statistical comparisons were not performed on data other than the catecholamine levels, it was found that adrenaline levels were consistently higher 60-240 min after the 600-mg dose relative to placebo, and higher 60-150 min after the 600-mg dose relative to the 150-mg dose. Sleep latencies, sleepiness scores, and reaction times correlated with serum caffeine levels in the predicted direction, showing that caffeine improved alertness in a dose-dependent fashion. 

A discussion of the detailed results of Hindmarch et a/. s (1991) study is beyond the scope of this book, but three general conclusions that can be drawn from their findings are worth noting here. First, some drugs can have a positive effect on performance - at least in tiie short run. Exan les are nicotine and caffeine that typically improve performance relative to placebo. This is particularly importmt because in most experimental drug and alcohol studies subjects are instructed not to smoke or drink coffee for several hours before the experiment. In contrast, in real-life people often smoke and drink coffee which can - at least to some extent -counteract the effects of a depressant. The consistently positive effects of caffeine on fatigue... 

Despite the controversy among scientists concerning the ergogenic potential of caffeine on sport performance, it is accepted that caffeine will not improve performance during short-term, high-intensity work, whereas an increase in both work... 

Ideally, to establish a causal relationship between caffeine and improved athletic performance, evidence would be obtained from epidemiological population studies, followed by careful, double-blind, placebo controlled experimental protocols isolating the purported etiological agent (caffeine), and eventually culminating with strong laboratory findings... 

Cole and co-workers67 examined perceived exertion and work output using a cycle ergometer with 10 healthy males, 8 of whom were classified as caffeine naive. In the experimental trials, subjects consumed 6 mg/kg caffeine 1 h before testing. Caffeine significantly improved work performance, even though the perception of effort was held constant for each trial. Subjects did more work on caffeine even while they were instructed to work at a predetermined RPE during both experimental and placebo trials. 

Perhaps the most intriguing perspective is that caffeine s major effects have little to do with muscles and fat metabolism but result from its psychostimulant effects, enhancing mood, improving attitude towards exercise, and thus motivating athletes to work harder and longer. This would account for its purported inability to alter strength, which may be a less psychologically malleable variable, while endurance performance is sometimes believed to be more amenable to force of will. 

Graham et al.79 noted that more than a quarter of Canadian youth surveyed reported use of caffeine during the last year to improve their athletic performance. The current allowable levels of caffeine permitted by the IOC are well above the minimum dose needed to elicit an ergogenic effect. If the IOC and other regulatory bodies are serious about controlling the use of performance enhancing drugs, then it may be necessary to ban caffeine entirely from competition. 

Results showed that both novelty and white noise improved recall performance under placebo and decreased it under caffeine.6 It appears that the additional arousal generated by novelty and white noise served to push caffeine subjects over the top of the inverted-U curve and hence decrease their recall performance. Thus, it may be that caffeine does improve memory performance under conditions that otherwise produce low arousal. However, any condition causing overarousal, whether or not it is a part of the memory task itself, can yield performance decrements. 

The results of these two studies and others provide further support for the theoretical inverted U-shaped arousal function. In the first case,93 high doses of caffeine pushed subjects over the top of the curve and hence impaired vigilance performance. As time passed and the subject became more accustomed to the experimental situation, arousal returned to more optimal levels and performance improved. In the second study,94 caffeine combined with moderately high intensity situational stimulation (white noise) to drive arousal up beyond the point of transmarginal inhibition and, again, decrease performance. 

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