Quantitative Muscle Analysis Measurements in Low Disability Multiple Sclerosis

Background:

People with multiple sclerosis (MS) having minimal physical disability often report motor fatigue following physical activity that is not captured by standard neurological testing.  Quantitative Muscle Analysis (QMA) objectively measures strength and motor fatigue (reduction in the maximal capacity to generate force over time) using strain gauges with computer-assisted technology. In people with MS having moderate disability, previous studies have shown significantly greater motor fatigue as compared to healthy volunteers (HV) using QMA.

Objectives: To determine if there are measurable differences in static fatigue in subjects with MS having low disability as compared to HV using QMA.

Methods:

10 male subjects with MS and low disability (EDSS 1-2.5) and 10 age/gender-matched HV participated in this study. The subjects with MS were highly functioning and physically active but reported experiencing motor fatigue when performing intense physical activity. QMA was used to test participants’ handgrip and knee extensor muscle strength on the dominant side. MVIC (maximal voluntary isometric contraction) and static fatigue test (SFT) were calculated for each muscle group.

Results: Mean SFT effort of all subjects included in the analysis exceeded 94% for both muscle groups (hand grip and knee extensor).  Subjects with MS had significantly weaker maximum grip in both MVIC and fatigue testing.  Subjects with MS also had significantly greater fatigue based on the 5-30s fatigue index with both muscle groups, however no significant differences were seen after the 30s time point.  Subjects with MS fatigued 25% significantly faster in both muscle groups.  The 50% exhaustion time detected significant differences in grip but not knee extensors. The rate of fatigue in both muscle groups was greater in HV during middle and late time periods and for the entire 100s trial.  Slopes were significantly different between groups at all of these time points except for 30-60s interval for the knee extensor muscles.

Conclusions:

Subjects with MS fatigued to a greater extent and reached exhaustion earlier than HV.  The patient cohort in this pilot study had low levels of disability suggesting that QMA testing may offer sensitive measurements even in early stages of disease.  Such instrumented measures of function may prove useful for targeted rehabilitation interventions as well as outcomes measures in clinical trials.