Prolonged cortical silent period is related to poor fitness and fatigue, but not tumor necrosis factor, in Multiple Sclerosis.
OBJECTIVE
Poor fitness among people with Multiple Sclerosis (MS) aggravates disease symptoms. Whether low fitness levels accompany brain functioning changes is unknown.


METHODS
MS patients (n = 82) completed a graded maximal exercise test, blood was drawn, and transcranial magnetic stimulation determined resting and active motor thresholds, motor evoked potential latency, and cortical silent period (CSP).


RESULTS
Sixty-two percent of participants had fitness levels ranked below 10th percentile. Fitness was not associated with disability measured using the Expanded Disability Status Scale (EDSS). Regression analyses revealed that, cardiorespiratory fitness, when controlling for disease demographics, contributed 23.7% (p < 0.001) to the model explaining variance in CSP. Regression analysis using cardiorespiratory fitness and CSP as predictors showed that CSP alone explained 19.9% of variance in subjective fatigue (p = 0.002). Tumor necrosis factor was not associated with any variable.


CONCLUSION
Low fitness was associated with longer CSP in MS. Longer CSP was, in turn, related to greater MS fatigue.


SIGNIFICANCE
MS patients had extremely low levels of cardiorespiratory fitness. Poor fitness predicted longer CSP, a marker of greater intracortical inhibition, which was linked to MS fatigue. Future research should examine whether aerobic training could shorten CSP and potentially lessen inhibition of cortical networks.
['Chaves|Arthur R|AR|', 'Kelly|Liam P|LP|', 'Moore|Craig S|CS|', 'Stefanelli|Mark|M|', 'Ploughman|Michelle|M|']
D000328:Adult D000072599:Cardiorespiratory Fitness D002540:Cerebral Cortex D019054:Evoked Potentials, Motor D005260:Female D006801:Humans D008297:Male D008875:Middle Aged D009103:Multiple Sclerosis D018763:Muscle Fatigue D011712:Pyramidal Tracts D011930:Reaction Time D014409:Tumor Necrosis Factor-alpha
Cortical silent period Fatigue Tumor necrosis factor Multiple Sclerosis Transcranial magnetic stimulation Cardiorespiratory fitness Corticospinal excitability