Somatosensory processing in long COVID fatigue and its relations with physiological and psychological factors

This study aimed to quantify somatosensory processing in long COVID and examine interactions between somatosensory processing, fatigability, state fatigue, trait fatigue, autonomic function, mood and illness beliefs. Eighty-eight participants (44 long COVID and 44 controls) completed at least one testing session involving either a cognitive or physical task. Pre and post-task measures included somatosensory processing, state fatigue, perceived effort, and heart rate variability (HRV). Trait fatigue, autonomic symptoms, mood, and illness beliefs were assessed using validated questionnaires. Group differences and task-related changes were analysed using multivariate and linear mixed models. There was no multivariate effect of group on baseline somatosensory attenuation or gating (p = .172), nor did these measures change following exertion, or associate with post-exertion fatigue. Long COVID participants reported greater fatigue than controls, with 64% meeting criteria for severe fatigue. State fatigue was greater at baseline, throughout both exertion tasks (all p <.001), and increased more during both tasks compared with controls. Despite this, cognitive and physical performance improved similarly across the task, with no group differences in fatigability (p = .199–.441). Long COVID resting HRV was lower, indicating autonomic dysfunction, but was not associated with fatigue. Only group status (p < .001) and pre-task fatigue (p < .001) were associated with post-exertion fatigue. Within long COVID participants, greater depression (p < .001) and perceived illness threat (p = .033) were associated with higher trait fatigue. The absence of somatosensory attenuation or gating abnormalities provides no support for sensory attenuation models of fatigue in long COVID.