Fatigability is one of the most prevalent disorder in MS followed by walking, balance and cognitive disorders. However, there are few experimental studies on the effects of fatigability on balance and gait hampering the knowledge of causal fatigue-related changes of walking, balance and cognition. Nowadays, instrumented systems such as wearable devices and optoelectronic systems are available and can be used to provide quantitative and objective indexes useful to monitor the changes of gait parameters during a fatiguing performance. (Moreover), instrumented assessment of patients' performances in dual task paradigms can reveal the possible impact of fatigability on cognitive functions. So far, high intensity functional training has been already used in MS to reduce fatigability. However, the true impact of reduced fatigability on walking, balance and cognition has not been assessed after a fatiguing task making impossible to understand the real impact of treatments focusing on fatigability on these functions. Thus, the aims of the present proposal are to assess the: 1) the acute effect of experimentally induced motor fatigability on walking, balance and cognitive functions using an objective instrumented assessment before, during, and after an overground fatiguing walking test. 2) to investigate the effect of high intensity multimodal functional training to improve motor and cognitive disorders.