Fatigue models for applied research in warfighting.
The U.S. Department of Defense (DOD) has long pursued applied research concerning fatigue in sustained and continuous military operations. In 1996, Hursh developed a simple homeostatic fatigue model and programmed the model into an actigraph to give a continuous indication of performance. Based on this initial work, the Army conducted a study of 1 wk of restricted sleep in 66 subjects with multiple measures of performance, termed the Sleep Dose-Response Study (SDR). This study provided numerical estimation of parameters for the Walter Reed Army Institute of Research Sleep Performance Model (SPM) and elucidated the relationships among several sleep-related performance measures. Concurrently, Hursh extended the original actigraph modeling structure and software expressions for use in other practical applications. The model became known as the Sleep, Activity, Fatigue, and Task Effectiveness (SAFTE) Model, and Hursh has applied it in the construction of a Fatigue Avoidance Scheduling Tool. This software is designed to help optimize the operational management of aviation ground and flight crews, but is not limited to that application. This paper describes the working fatigue model as it is being developed by the DOD laboratories, using the conceptual framework, vernacular, and notation of the SAFTE Model. At specific points where the SPM may differ from SAFTE, this is discussed. Extensions of the SAFTE Model to incorporate dynamic phase adjustment for both transmeridian relocation and shift work are described. The unexpected persistence of performance effects following chronic sleep restriction found in the SDR study necessitated some revisions of the SAFTE Model that are also described. The paper concludes with a discussion of several important modeling issues that remain to be addressed.
Hursh
Steven R
SR
Science Applications International Corporation, Biomedical Modeling and Analysis Program, Joppa, MD 21085, USA. hurshs@saic.com
Redmond
Daniel P
DP
Johnson
Michael L
ML
Thorne
David R
DR
Belenky
Gregory
G
Balkin
Thomas J
TJ
Storm
William F
WF
Miller
James C
JC
Eddy
Douglas R
DR
D001359:Aviation; D002940:Circadian Rhythm; D003071:Cognition; D005221:Fatigue / Q000209:etiology / Q000503:physiopathology*; D006801:Humans; D008887:Military Medicine; D008954:Models, Biological; D012106:Research; D012892:Sleep Deprivation / Q000150:complications / Q000503:physiopathology*; D012984:Software; D013647:Task Performance and Analysis; D014481:United States; D014857:Warfare