Caffeine for the Sustainment of Mental Task Performance Formulations for Military Operations (2001) / Chapter Skim
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3 Efficacy of Caffeine
3 Efficacy of Caffeine
Pages 33-46
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From page 33... ...
Recent research indicates that caffeine may also act by altering pain perception since it has been reported to increase plasma p-endorph~ns during endurance exercise (Laurent et al., 2000~. Typically, the magnitude of the exercise response far exceeds and masks the resting effects of caffeine intake.
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From page 34... ...
The dose of caffeine required for significant improvements in physical performance ranges from 3 to 9 mg/kg (Graham and Spriet, 1995~. It should be
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From page 35... ...
to a carbohydrate-electrolyte solution and examined the effects on substrate metabolism and endurance performance time in 15 trained subjects during a 1-hour time trial. The addition of caffeine to the carbohydrate-electrolyte drink resulted in a significant improvement in the performance times as compared to placebo or carbohydrate-electrolyte drink alone, with a maximum effect at an intake of about 3 mg of caffeine per kilogram There was no apparent change in metabolic fuel used during the cycling exercise, thus ruling out fuel shifts as the mechanism by which caffeine augmented the carbohydrate effect.
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From page 36... ...
The small number of subjects in this experiment makes it difficult to project these findings to all other populations, including military personnel. Other Effects on Physical Performance It has been postulated that caffeine might impinge on physical performance via changes in body temperature and fluid balance.
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From page 37... ...
However, a review of the experimental literature reveals inconsistencies in the amount of caffeine that is required to produce positive effects on cognitive behavior. These discrepant findings can be explained by differences among experiments in a number of variables including whether or not subjects were tested following a period in which they had abstained from using caffeine, the tasks used to assess cognitive behavior, the age and gender of the subjects, the subjects' history of caffeine use, and whether the subjects were rested or sleep deprived.
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From page 38... ...
caffeine users that caffeine administered in 250-mg doses twice a day compared to placebo improved daytime alertness and reaction time on auditory vigilance tasks. Kenemans and Lorist (1995)
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From page 39... ...
Following caffeine ingestion, blood pressure increased significantly above baseline for older men whereas it remained statistically unchanged in younger men. Heart rates in both groups were unaffected by caffeine ingestion.
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From page 40... ...
Alertness has been assessed using objective measures such as ambulatory vigilance monitors, visual and auditory vigilance tasks, and subjective measures such as self-reports and questionnaires. Studies using these measures have found that sleep deprivation impairs performance on vigilance tasks and decreases self-reports of alertness (Bonnet and Arand, 1994a,b; Bonnet et al., 1995; Caldwell et al., 1995; Penetar et al., 1993~.
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From page 41... ...
Restoration of Sleep Deprivation-Induced Cognitive Deficits with Sleep All of the above-listed decrements in cognitive behavior can best be reversed by reconstituting sleep. There is a dose effect for the restorative effects of sleep duration on cognitive performance (Bonnet, 1999; Bonnet and Arand, 1994b; Bonnet et al., 1995~.
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From page 42... ...
Performance was measured by a visual reaction time test, and mood was assessed using the Stanford Sleepiness Scale (SSS)
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From page 43... ...
With respect to mood, caffeine administration in sleep-deprived subjects decreased reports of confusion and fatigue and increased reports of vigor, but had no effect on reports of tension, anger, and depression using the POMS (Kautz, 1999~. Using visual analog scales, caffeine intake led to reports of decreased sleepiness and increased alertness, ability to concentrate, confidence, talkativeness, energy levels, anxiety, jitteriness, and nervousness (Kautz, 1999~.
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From page 44... ...
The role of caffeine-carbohydrate combinations in enhancing physical performance still needs to be clarified. Evidence is presented that caffeine can enhance certain types of cognitive performance, most notably vigilance and reaction times, in rested individuals
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From page 45... ...
When naps are not an option, caffeine alone could be used to partially alleviate sleep deprivation-induced impairments in cognitive behavior. Combining naps with judicious caffeine use may be the best remedy for sleep deprivation-induced decrements in cognitive function in military situations where adequate sleep cannot be obtained.
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From page 46... ...
and also causes changes in cerebral blood flow leading to vasodilation in high caffeine users that is thought to be associated with a throbbing, vasculartype headache, one of the most commonly observed caffeine withdrawal symptoms (Couturier et al., 1997; Lader, 1999; Mathew and Wilson, 1985~. This withdrawal phenomenon could lead to decrements in performance during military operations and thus should be avoided.
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