Fatigue-Induced Postural Instability During Dual-Tasks in Women with MS: Influence of Muscle Strength.

There is a lack of research on the effects of fatigue and dual-task motor performance in people with Multiple sclerosis (MS), especially in women. Using a group of 20 women with MS and 20 healthy controls, we examined the effects of fatigue and attentional demands on center of pressure (COP) displacements during upright stance. Anterior-posterior (AP), Media-lateral (ML), and total COP displacements, and also ankle plantar flexors' strength were measured. Results indicated that fatigue and dual-task resulted in higher ML COP displacements in both groups, but unlike controls, MS patients had higher ML displacements during the dual-task compared to single-task trials. Additionally, while fatigue resulted in an increased single-task AP and total COP displacements in both groups, it yielded higher dual-task AP and total COP displacements only in MS patients. Moreover, MS patients had weaker ankle plantar flexors compared to healthy controls, but the plantar flexors-mainly soleus-maximum voluntary contraction (MVC) was only associated with fatigued single-task balance performance in MS patients. Our study confirmed the adverse effects of fatigue and dual-task on balance performance, especially in MS patients. Further research is required on whether the modulation of balance performance of ankle plantar flexors' MVC depends on fatigue and attentional task demands.