Fatigue is a major symptom across a broad range of diseases and is an important cause of disability and reduced quality of life. Fatigue is a subjective symptom and should be distinguished from performance fatigability which is a decline in an objective measure of performance. Understanding the mechanisms giving rise to performance fatigability, and its contribution to fatigue, is critical for developing effective therapies against fatigue which are currently lacking.
During muscle contractions, performance fatigability arises from changes in muscle activation by the central nervous system (CNS) and changes within the muscle itself. In this thesis of Roeland Prak, we studied the effect of chronic disease and injury on performance fatigability using a 2-minute maximal contraction of a hand muscle. Paired with electrical nerve stimulation and functional neuroimaging of the brain, this setup allowed us to distinguish and monitor processes in the central nervous system and the muscle giving rise to performance fatigability.
Studying persons with spinal cord injury, mild traumatic brain injury, and Sjögren’s syndrome allowed for comparisons across conditions where fatigue is a frequent complaint. Spinal cord injury and Sjögren’s syndrome groups had difficulty sustaining muscle activation during a 2-minute contraction indicating failure within the central nervous system. In contrast, we did not find differences in performance fatigability between persons with mild traumatic brain injury and healthy controls. Furthermore, we found that fatigue severity is not always associated with performance fatigability.
In conclusion, the central nervous system contribution to performance fatigability should always be considered. Moreover, performance fatigability can complement but not substitute subjective measures of fatigue.
