Leg power asymmetry and postural control in women with multiple sclerosis

The extent of and the interactions between muscle strength, walking speed, postural control, and symptomatic fatigue in multiple sclerosis (MS) are not known, nor are the effects of bilateral strength asymmetries on these variables.

To quantify the magnitude of and the associations between bilateral strength and limb-loading asymmetries, postural control, and symptomatic fatigue in women with MS.

Peak knee extensor (KE) and dorsiflexor (DF) isometric torque and isotonic power were assessed bilaterally in 12 women with MS (Expanded Disability Status Scale = 4 +/- 1) and 12 age-matched female controls using a Biodex dynamometer (Biodex Medical, Shirley, NY). Center of pressure (CoP) variability during 20 s of quiet stance was measured in the anteroposterior (AP) and the mediolateral (ML) directions using adjacent force plates. Bilateral asymmetry scores were calculated for power and torque. Normal and brisk walk times (25 ft) and symptomatic fatigue (Visual Analog Fatigue Scale and Fatigue Severity Scale) were measured before strength and balance testing.

Fatigue was greater and walk times (normal and brisk) were longer in MS (P < or = 0.01). Dorsiflexor (DF) isometric torque and power and knee extensor (KE) isometric strength were similar between groups. KE power was lower (mean +/- SD = 21.5 +/- 16.2%; P < or = 0.05) and KE power asymmetry was greater in MS than in controls (9.2 +/- 6.9%; P = 0.02). Postural variability of the CoP was greater in the AP direction in MS than in controls (7.52 +/- 3.02 and 4.33 +/- 1.79 mm, respectively; P = 0.005). KE power asymmetry was associated with fatigue and walk times (P < or = 0.02), and AP CoP variability was correlated with fatigue, walk times, and power asymmetries (P < or = 0.05).

These data provide new evidence of a potential role for KE strength asymmetries in the symptomatic fatigue and physical dysfunction of persons with MS, possibly through an effect on postural stability.