Inclusion Criteria:

For people with MS:

• - Clinically definite multiple sclerosis according to the revised McDonald criteria.

• - People with EDSS ≤ 5.0.

• - People with MS who experience foot drop.

• - Able to walk at least 200 meters unassisted, i.

e without walking aids. For healthy participants:

• - Not been diagnosed with any neurological disease or have any other condition or injury which will affect walking ability.

Exclusion Criteria:

For people with MS:

• - Clinically diagnosed relapse within the last month.

• - Any musculoskeletal impairment that can affect walking ability.

• - Cognitive impairments; with a score in the Multiple Sclerosis Neuropsychological Screening Questionnaire (MSNQ) ≤ 75.

• - Depression and anxiety; with a score in Hospital Anxiety & Depression Scale (HADS) > 10.

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.#46;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.

Arms

Other: MS group

This group will perform walking trials in various conditions, i.e. normal walking, walking whilst performing an attention demanding task and walking while being physically tired.

Interventions

Other: - Incremental shuttle walk test

In the incremental shuttle walk test, participants will have to walk between two cones (10m distance) several times. The time they will have to cover the distance between the two cones (signified by 'bleeps') will become increasingly shorter, until they cannot get to the next cone before the next 'bleep'. This test will last a maximum of 20 minutes. In the Stroop test, the words of four colours, but written with a different colour, will be projected on the wall in front of participants and they will need to identify the colour of the text and ignore the word itself.