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Collecting Sleep, Circadian, Fatigue, and Performance Data in Complex Operational Environments

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The Sleep Regularity Index: A New Way to Evaluate Shiftwork Schedules.

Jacob R Guzzetti¹, Panagiotis Matsangas², Siobhan Banks¹

¹Behaviour-Brain-Body Research Centre, University of South Australia, Adelaide, South Australia, Australia.

Journal of Sleep Research

|July 1, 2025

Summary

Sailors

Keywords:

maritime defence sleep restriction sleep timing sleep variability watchkeeping

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Area of Science:

Maritime Health
Sleep Science
Occupational Physiology

Background:

Sailors face challenging shiftwork schedules ('watchbills') impacting sleep and wellbeing.
Previous research on watchbills primarily focused on sleep duration, yielding mixed results.
Sleep regularity, a crucial sleep dimension, is understudied in naval populations.

Purpose of the Study:

To evaluate the utility of sleep regularity assessment in comparing sailors' watchbills.
To utilize the Sleep Regularity Index (SRI) as a novel metric for watchbill evaluation.
To investigate how different watchbills affect sleep regularity among naval personnel.

Main Methods:

Assessed 218 sailors across various watchbills over a one-week underway period.
Measured sleep patterns using objective methods to calculate the Sleep Regularity Index (SRI).
Compared SRI scores across different watchbill schedules, controlling for sleep duration.

Main Results:

The 5-h on/15-h off watchbill exhibited a significantly lower median SRI compared to other schedules.
No significant differences in daily sleep duration were found between the 5-h on/15-h off watchbill and others.
Median SRI scores were comparable among fixed watchbills, indicating consistent regularity.

Conclusions:

Sleep regularity assessment, using the SRI, offers valuable insights into watchbill effectiveness.
SRI effectively differentiates watchbills, especially when sleep duration is similar.
This metric can inform the development of healthier and more sustainable watch schedules for sailors.