THE USE OF CAFFEINE VERSUS PROPHYLACTIC NAPS IN SUSTAINED PERFORMANCE

Previous studies have shown that performance during sleep loss is impr oved by prophylactic naps as a function of varying nap length. Based o n single-dose caffeine studies, a similar dose-response effect has bee n hypothesized on performance, alertness and mood during sleep loss. T he present study compared the effects of repeated versus single-dose a dministration of caffeine and varying amounts of sleep taken prior to sleep loss on performance, mood and physiological measures during 2 ni ghts and days of sleep loss. A total of 140 normal, young adult males participated at one of two study sites. Ninety-eight subjects at one s ite were randomly assigned to one of four nap conditions (0, 2, 4 or 8 hours) and 42 subjects at the second site were assigned to one of fou r caffeine conditions. After a normal baseline night of sleep and morn ing baseline tests of performance, mood and nap latency, subjects in t he nap groups returned to bed at noon, 1600 hours, 1800 hours or not a t all. Bedtimes were varied so that all naps ended at 2000 hours. Subj ects in the caffeine groups received either a single 400-mg dose of ca ffeine at 0130 hours each night or repeated doses of 150 or 300 mg eve ry 6 hours starting at 0130 hours on the Ist night of sleep loss. A pl acebo control group (no nap and placebo administered every 6 hours on the repeated caffeine schedule) was run at both sites. Subjects remain ed awake and followed the same schedule of computer-administered perfo rmance tests, mood scales, multiple sleep latency test observations an d meals/breaks for 52 hours before being allowed a recovery night of s leep at their normal sleep time. Results are consistent with previous findings and suggest that performance, mood and alertness are directly proportional to prophylactic nap length. Furthermore, an 8-hour nap i s superior in maintaining performance, mood and alertness to either si ngle or repeated caffeine administrations. Naps, in general, provided longer and less graded changes in performance, mood and alertness than did caffeine, which displayed peak effectiveness and loss of effect w ithin about 6 hours. Shorter prophylactic naps and small repetitive do ses of caffeine, however, did maintain performance, mood and alertness during sleep loss significantly better than no naps or large single d oses of caffeine. Neither nap nor caffeine conditions could preserve p erformance, mood and alertness near baseline levels beyond 24 hours, a fter which levels approached those of placebo.