The Relations between Psychological Flexibility Fatigue and Sleep Disturbance
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Objective: Fatigue is a common, disabling problem which usually co-occurs with sleep disturbance. Psychological flexibility (PF) could have a positive role in sleep disturbance and fatigue. This cross-sectional study examined this role and whether there are indications for a mediating effect of sleep disturbance in the relation between psychological flexibility and fatigue. Methods: Participants (N=339) completed an online survey, measuring psychological flexibility with The Flexibiliteits Index Test (FIT-60), fatigue using the energy scale of The Rand Short Form 36 (SF-36) and sleep disturbance using Insomnia Severity Index (ISI). These associations were examined with regression analysis. Results: People who have low PF and more severe sleep problems reported more fatigue. For high levels of sleep disturbance, the association between PF and fatigue was low. For people with low PF, there was not a strong relationship between sleep disturbance and fatigue but for people with high PF, this association was stronger. The components acceptance, being present, values and committed action had the strongest associations with fatigue. There was a negative correlation between PF and sleep disturbance, and a positive correlation between sleep disturbance and fatigue consistent with other studies. PF and fatigue were negatively correlated and sleep disturbance mediated this relationship. Discussion: The findings tentatively suggest that improving psychological flexibility might have an impact on fatigue but this requires further research on causality. It is also worth trying to treat sleep disturbances in addition to improving PF, because it may be more beneficial to reduce fatigue.