Discriminating Between Fatigue and Sleepiness in the Naval Operational Environment.

OBJECTIVE: To assess the similarities and differences between reported levels of fatigue and sleepiness as a consequence of working at sea.

PARTICIPANTS: 767 crewmembers of a U.S. Navy ship.

METHODS: Retrospective analysis of a survey to include questions about demographics, caffeine consumption, sleep adequacy, the Epworth Sleepiness Scale (ESS), and the Fatigue Severity Scale (FSS).

RESULTS: ESS scores (8.41 ± 4.66) indicated that 32% of the participants had excessive daytime sleepiness (ESS score > 10), while approximately 7% had an ESS score of 16 or more. FSS scores (average FSS = 3.01 ± 1.37) indicated that 28% of the participants had elevated fatigue (FSS score ≥ 4). Even though ESS and FSS scores were correlated (r = 0.39), their association explained only 15% of the variability observed. In terms of behavioral and lifestyle patterns, crewmembers with elevated fatigue (FSS ≥ 4) reported getting less exercise than those reporting less fatigue. Individuals with excessive sleepiness (ESS > 10) reported higher caffeine consumption. Crewmembers with elevated fatigue and comorbid sleepiness (FSS ≥ 4 and ESS > 10) reported receiving less sleep than other crew members.

CONCLUSIONS: These results suggest that subjective fatigue and subjective sleepiness, as measured by the FSS and ESS scales, are distinct constructs and both are consequences of working at sea. The scores on the two scales correlate differentially with behavioral and lifestyle patterns of the crewmembers.