Longitudinal course of fatigue questionnaire scores for the fatigued and non-fatigued group. Longitudinal course of CIS-20R total scores for the severely fatigued group (black circles, n = 65) and non-fatigued group (white squares, n = 428). Fatigue severity was assessed before deployment (T0) and 1 month (T1) and 6 months (T2) after return from deployment. The longitudinal course of CIS-20R scores differed between the two groups (time: F(1.98, 970.51): 138.17, P < 0.001; group: F(1,491): 283.73, P < 0.001; interaction effect time x group: F(1.98, 970.51): 118.40, P < 0.001). However, participants with severe fatigue at T2 had higher fatigue questionnaire scores than the non-fatigued group at all assessment points (T0: P < 0.001, T1: P < 0.001, T2: P < 0.001). Data are presented as mean ± SEM. ***P < 0.001.