Modeling the Effect of Days Underway and Environmental Motion on Crew Physical Activity on Naval Vessels

Results from earlier research on crew activity onboard naval vessels suggest that personnel activity is a function of two components, time underway, and ship motion severity. Physical activity reduction was attributed to some combination of sopite syndrome and motion-induced fatigue. Although both stressors are a well-recognized problem in the naval environment, few studies have addressed them. Building on earlier findings, this work proposes a mathematical model to account for the effect of motion and days underway on the observed personnel physical activity. Model predictions are evaluated against a retrospective analysis of existing actigraphic recordings from three earlier projects in the naval operational environment. Analysis showed that the model predicts activity with a good approximation. These results further validated the effect of the days underway and motion component in predicting personnel activity. The observed reduction in physical activity may be a valuable surrogate indicator of sopite syndrome and motion-induced fatigue. Future research efforts should incorporate the effect of sleep, mission requirements, and the occupational component of crew physical activity.