We aimed to quantify somatosensory processing in long COVID and interactions between somatosensory processing, fatigability, fatigue, autonomic function, mood and illness beliefs. Eighty-eight participants (44 long COVID and 44 controls) were invited to complete two testing sessions, where fatigue was induced by either a cognitive or a physical task in a cross-over design; all participants completed at least one session. Baseline questionnaires assessed trait fatigue, autonomic symptoms, mood and illness beliefs. Pre- and post-task measures included somatosensory processing, state fatigue, perceived effort and heart rate variability (HRV). Group differences and task-related changes were analysed using multivariate and linear mixed models. There was no multivariate group effect on baseline somatosensory measures (P = 0.172), nor did they 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 < 0.001), and increased more during exertion compared with controls. Despite this, cognitive and physical performance changed similarly across tasks, with no group differences in fatigability (P = 0.199-0.441). Long COVID participants had lower resting HRV, indicating autonomic dysfunction, but HRV was not associated with fatigue. Only group status (P < 0.001) and pre-task fatigue (P < 0.001) were associated with post-exertion fatigue. Within long COVID participants, greater depression (P < 0.001) and perceived illness threat (P = 0.033) were associated with greater trait fatigue. The absence of somatosensory abnormalities provides no support for the sensory attenuation model of fatigue in long COVID.
Long Covid