Relationship Between Fatigability and Perceived Fatigue Measured Using the Neurological Fatigue Index in People with Multiple Sclerosis

Background: Understanding the relationship between perceived fatigue and performance fatigability could lead to more effective interventions to manage multiple sclerosis (MS)–related fatigue. However, the relationship between self-perceived fatigue measured using the Neurological Fatigue Index (NFI-MS) and performance fatigability in people with MS is unknown. We sought to explore the relationship between the NFI-MS and performance fatigability in people with MS. Methods: Fifty-two participants (mean ± SD age, 46.8 ± 10.1 years) completed the study. Three measures of performance fatigability were used: percent change in meters walked from first to last minute of the 6-Minute Walk Test, percent change in force exerted from first to last trial on a repetitive maximal hand grip test, and response speed variability on the Continuous Performance Test. Perceived physical and cognitive fatigue were measured using the NFI-MS. The state level of fatigue was examined immediately before and after performing the fatigability measures using a one-item visual analogue fatigue scale. Results: Of the three performance fatigability measures, only the attentional task (response speed variability) was significantly associated with NFI-MS physical (r = 0.326, P = .020) and cognitive (r = 0.276, P = .050) domain scores. Participants demonstrated significantly higher state levels of fatigue after performing all performance fatigability measures (P ≤ .001). Conclusions: The NFI-MS and the performance fatigability measures used in this study are easy to administer. We encourage wider use of these measures in clinical and research settings for comprehensive assessment of MS-related fatigue.