## 1 Introduction  
Multiple sclerosis (MS) is a chronic and demyelinating disease of the central nervous system [1]. The reported prevalence in 2020 was 35.9/100,000 people. Furthermore, a comparison with 2013 data shows that the prevalence of this disease is increasing [2]. Moreover, this condition constitutes the most common cause of neurological disability in young adults after spinal cord injury [3]. MS is a chronic disease characterised by a wide variety of clinical manifestations that patients can suffer from. The most common symptoms in MS are a loss of stability and coordination, spasticity and muscle weakness, fatigue, somatosensory dysfunctions, and visual impairments [4, 5]. Cognitive disturbances [6] and some movement disorders such as myoclonus, ballism, or parkinsonism [7] are other symptoms that MS patients may experience.  
Stability deficit is one of the most debilitating problems for patients and is characterized by an increased sway in a standing position, delayed responses to postural perturbations, and a reduced capacity to move toward the limit of stability [8]. Static and dynamic stability impairment is associated with an increased risk of falls and leads to a reduction in the patient's function [9] and quality of life [10]. Several studies have shown the benefits of stability training in MS patients. Some stability training programmes (e.g., conventional physiotherapy, virtual reality, core training, dual tasks, integration of sensory stimuli) have been shown to be effective in improving static and dynamic stability, reducing the number of falls, increasing the walking speed, and improving the self-perceived stability and quality of life [11; 12; 13; 14; 15; 16].  
One of the elements that can contribute to improved stability is the activation capacity of the intrinsic foot muscles (IFMs). [PERSON] et al. [17] showed that the _abductor hallucis_ and _abductor digiti minimi_ muscles play an important role in modulating static stability by increasing their activation in response to disturbances in the visual or vestibular systems. In addition, many authors have found that IFM training leads to a significant increase in static and dynamic stability in healthy subjects of different age groups, as well as in subjects with musculoskeletal disorders such as chronic ankle instability [18; 19; 20; 21; 22; 23]. Finally, the training of IFMs leads to other physical benefits such as greater toe flexor strength [22; 24], improvements in physical performance [24; 25], proprioception and self-perceived stability [19], decreased medial longitudinal arch drop under load [18; 24], and a reduction in the incidence of injury [26]. However, no studies have been found that have assessed the efficacy of an IFM training programme on the overall stability in patients diagnosed with MS. Considering that stability deficit is one of the most prevalent and limiting signs in MS patients and that IFMs have been shown to lead to improvements in stability, it seems important to study this association. The hypothesis of this study is that strengthening IFMs can lead to improvements in static and dynamic stability in MS patients.  
Thus, the main objective of the study was to assess the efficacy of an 8-week IFM training programme on the stability in patients with MS.