How Does Fatiguing Activity Alter Central and Peripheral Neuromotor Physiology in Persons with Multiple Sclerosis? a Systematic Review of the Literature

Background:  The fatigue commonly reported by persons with MS is complex and multifactorial. One theorized contributor to this fatigue is a reduction in muscle strength and functional capacity. These changes may be a result, in part, of altered neuromotor physiology, and may be exacerbated during and after fatiguing motor activity. It has been theorized that both peripheral and central mechanisms contribute to activity-induced changes in neuromotor physiology found in persons with MS. Changes in peripheral neuromotor physiology include altered muscle contractile properties and prolonged action potentials. Changes in central neuromotor physiology include increased conduction time, altered cortical activation, and reduced voluntary activation.  The implications and extent of how activity-induced fatigue affects neuromotor physiology in persons with MS is not fully understood.

Objectives: The purpose of this systematic review was to synthesize current knowledge about the effect of fatiguing activity on neuromotor physiology in persons with MS compared to persons without.

Methods: A search of the Ovid MEDLINE (1996-current) database was performed in August of 2014 to identify appropriate literature using the following keywords:  multiple sclerosis AND [muscle fatigue OR motor fatigue]. Articles were screened with the following inclusion criteria: experimental or quasi-experimental studies of a sample of persons with MS that measured changes in neuromotor physiology with fatiguing motor activity. Each article was then evaluated to determine the level of evidence using Sackett’s criteria.

Results: Fifty-five articles were found through the search. Of these, seven articles met all criteria and were included in this systematic review. All seven articles received a Sackett level of evidence rating of 2b.

Conclusions: In persons with MS, central neural processes appear to be more affected by fatiguing activity than peripheral processes. Evidence for activity-induced differences in peripheral neuromotor physiology (e.g. maximum volitional contraction, twitch-evoked force production) between healthy persons and those with MS is equivocal. However, activity-induced differences in central neuromotor physiology exist between these groups. Persons with MS have lower cortical activation levels and greater deficits in voluntary activation than persons without MS. This suggests that interventions that can improve central neuromotor drive may be more effective than those that target peripheral mechanisms to improve neuromotor function in people with MS.