People with Multiple Sclerosis (pwMS) often experience foot drop, which means that the foot is not adequately lifted from the ground when walking. Functional Electrical Stimulation (FES) is applied to the shin muscles to aid lifting the foot of the ground and reduces the risk of trips and falls. PwMS that are users of functional electrical stimulation (FES) report that one of the benefits is that it reduces the mental effort of walking and that as a result less concentration is needed when they walk. Motor fatigability, which is the reduced ability of the muscles to produce force or power, also negatively affects the walking performance of pwMS. There have been several studies showing the benefits of FES to the walking of pwMS, but not while performing two tasks at the same time and experiencing fatigability resembling more daily life conditions. The proposed study aims to investigate the direct orthotic effect of FES (FES on vs off) in three different conditions, which include just walking, walking while performing an attention-demanding task and walking with an attention-demanding task after having completed a fatiguing task. The study design of this research allows the quantification of benefits of the use of FES which have until now only be reported subjectively.