Fatigue, both physical and cognitive, is one of the most prevalent and disabling symptoms experienced by persons with multiple sclerosis (MS). Cognitive fatigability (CF) is characterized as the inability to maintain optimal performance throughout the duration of a cognitive task. Typically, cognitive impairment worsens with disability progression in MS; however, research examining CF has been limited to persons with MS who have lower disability. Furthermore, there is evidence that cardiorespiratory fitness (CRF), an indicator of exercise training, is positively correlated with cognitive performance in persons with MS; however, the relationship between CRF and CF in MS remains unknown.
The primary objective of this study was to characterize CF in persons with MS with advanced disability and to explore the relationship between CF and CRF.
A cross-sectional examination of 20 persons with MS with advanced disability was conducted ((mean age=60.1±10.5) years; 80% female; median EDSS=7.0 (IQR=1.0)). Participants completed a cardiopulmonary exercise test on a recumbent stepper with continuous monitoring of oxygen consumption (VO2). The 3-second version of the Paced Auditory Serial Addition Test (PASAT) was used to measure the CF magnitude (CFM) within the sample, expressed as the difference in performance between the first third and last third of the test.
The mean±SD PASAT score for the sample was 42.9±10.6. The mean score for the first, second, and third third of the PASAT was 14.9±4.4, 14.6±4.9, and 13.5±5.5, respectively. The mean CFM was -1.5±2.4. Peak CRF (VO2peak) of the sample was 11.5±4.1 ml/kg/min, peak power output was 54.7±26.7 Watts (W), and participants reached VO2peak within 663.1±266.3 seconds. There was a significant correlation between total PASAT scores and VO2peak (rs=0.57; p=0.009), and between CFM and VO2peak (rs=0.46; p=0.04). No other statistically significant correlations were observed
The frequency of CF observed in the sample was greater than prior research, although the mean CFM obtained was comparable to other studies. A strong relationship was observed between CF and oxygen consumption (VO2peak); however, this relationship was not consistent across other physiological fitness indicators. These results support the possibility of examining exercise training, specifically aerobic exercise, in the management of CF in persons with advanced MS.
This study was supported, in part, by the Multiple Sclerosis Society of Canada [EGID 3255], the National Multiple Sclerosis Society [PP-1904-33937]; the Canadian Foundation for Innovation and the Ontario Research Fund