## 2 Materials and Methods
### Outcome Measures  
Static and dynamic stability and self-reported confidence were measured at baseline and after completing the eight-week IFM training programme. These variables were evaluated by one of the members of the research team ([PERSON]) who was blinded to the group to which the participants had been assigned.  
Dynamic stability was measured using the Four Square Step Test (FSST) and the Six Spot Step Test (SSST).  
[PERSON] et al. [29] described that FSST presents excellent inter- and intra-rater reliability (ICC 0.922) and very high sensitivity (89%) and specificity (85%) levels. The test consists of drawing a cross on the ground, delimiting four grids. The subject stands in square number 1 facing square number 2. The aim is to step as fast as possible into each square in the following sequence: square number 1, 2, 3, 4, 1, 4, 3, 2, and 1. This sequence requires the subject to step forward, backward, and sideways to the right and left. The score is recorded as the time taken to complete the sequence. The stopwatch starts when the first foot contacts the floor in square 2 and finishes when the last foot comes back to touch the floor in square 1. Two trials were completed with the best time taken as the score. A trial was repeated if the subject failed to complete the sequence successfully or lost balance.  
The SSST assesses lower limb function, particularly dynamic balance and coordination [30]. [PERSON] et al. [31] described that the SSST is a reproducible and valid test for MS patients with excellent reliability (ICC 95%: 0.983). The SSST was superior to short- and long-distance walk tests (6 MWT and T25 FWT) in detecting walking capacity impairments in MS patients [32]. The test field measured one metre (width) by five metres (length). In the middle of the width line (0.50 m), a cone was placed in the proximal and distal areas of the line (start point and finish point). On each lateral line, two cones were placed at distances of one and three metres on the left. Another two cones were placed at two and four metres on the right. The subjects were instructed to walk on alternating sides and to kick the cones, alternating between the medial and lateral sides of the same foot. The subjects were instructed to complete the test as quickly as possible, without running. The test was timed from lifting the foot from the start point until kicking the last cone. Two trials with each lower extremity were completed, and the best results were registered.  
Static balance was measured using the Frailty and Injuries: Cooperative Studies of Intervention Techniques test (FICSIT-4 test). This test presents good test-retest reliability (r = 0.66) [33]. Participants have to maintain four progressively difficult foot positions for 10 s each (side-by-side stance, semi-tandem stance, tandem stance, unipedal stance). Each standing position is scored as follows [34; 35]: zero points (holding the position less than one second); one point (holding the position two to nine seconds); two points (holding the position more than ten seconds). The sum of the four components yields the maximum score, which can be nine points (unipedal stance scores out of three points). Two trials were completed with the best result taken as the score.  
Participants were instructed to wear comfortable shoes to complete these three balance tests. Before the patient performed the test, the evaluator explained and demonstrated it to the subjects. Moreover, one practice trial was completed before the assessment trial.  
Self-perceived confidence regarding stability was measured using the Activities-specific Balance Confidence scale (AsBC) questionnaire. This is a validated and reliable self-reported instrument (ICC = 0.92) [36] that evaluates the patient's perceived of balance confidence during 16 different daily activities. Each item is scored from 0 to 100% (0% means not at all and 100% means fully confident). The final score is the mean value of all items. This questionnaire has been used in other studies to assess functionality in MS patients [37].