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2007, Piran, Slovenia

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Cognitive and Psycophysiological Function<br />

targets was faster (by almost 0.2 s), identification of both target types was higher (by<br />

about 4%), and the engagement times of foe targets were longer (by about 0.2 s) in<br />

latter two sessions compared to the first.<br />

EXERCISE FATIGUE (n = 12): Four trials were conducted, PP, PC, CP, and CC<br />

where P and C refer to placebo and caffeine ingestion, taken in the order indicated<br />

before and following exercise (respective caffeine doses were 5 and 2.5 mg⋅kg -1 body<br />

mass). Exercise began with a 2.5 h loaded (25 kg backpack) march at 6 km⋅h -1 and<br />

ended with a 1 h period of sandbag wall construction (20 x 15 kg bags moved and<br />

assembled back and forth across a 4.5 m room). Subjects were presented with two 10<br />

min shooting tasks involving 48 randomly appearing foe targets at 30 – 60 m range<br />

moving across a street (crossing times from 1.5 and 2.8 s), and a sentry duty task<br />

involving 30 lane pop-up foe targets at 200 m range appearing randomly for 4 s over<br />

two consecutive 1 h periods held between the two shooting tasks. Caffeine had no<br />

effect on marksmanship for both the street and sentry duty scenarios, except that the<br />

number of shots fired during the latter was slightly, but significantly, higher compared<br />

to PP. Caffeine also lowered the engagement time slightly, but significantly for CC<br />

(2.8 ± 0.3 s) compared to PP (3.0 ± 0.3 s) during sentry duty (engagement times for<br />

PC and CP were not affected).<br />

SLEEP DEPRIVATION (n = 20): Two trials were conducted, each involving 22 h of<br />

active wakefulness before target engagement testing began. Subjects were given 400,<br />

100, and 100 mg of caffeine (via chewing gum) or placebo at 7.5, 3, and 0 h prior to<br />

testing during the respective trials. They were presented with 15 hostile and 5 nonhostile<br />

lane pop-up targets at 200 m range that appeared for 4 s over two consecutive<br />

30 min sessions. Target engagement time was adversely affected by sleep deprivation,<br />

increasing from a baseline value of 3.03 ± 0.26 s to 3.29 ± 0.17 s during the placebo<br />

trial; however, it was restored (3.04 ± 0.25 s) during the caffeine trial, as seen in Fig.<br />

2. Similarly, caffeine also restored the number of shots fired, but not the number of<br />

hits. The overall ratios of hits to shots fired were fairly consistent across all conditions<br />

(56.8, 55.4, and 53.1% for BASELINE, PLACEBO, and CAFFEINE, respectively)<br />

thus indicating no affect of sleep deprivation or caffeine intervention on relative<br />

marksmanship.<br />

Figure. 2. Mean ± SE of target engagement times during both 30 min sessions, which was<br />

higher during PLACEBO than the other two conditions, and mean ± SE of the number of<br />

shots fired and number of hits during both 30 min sessions; * indicates a significant<br />

difference.<br />

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