Inclusion Criteria:

• - an MS diagnosis according to McDonald criteria; - an overall MS-disability score from 2.0 to 5.5 according to the Expanded Disability Status Scale; - ability to walk 100 m without aid; - a maximum score of 24 in the Mini-BESTest (i.e., < 25 points) - 18 to 65 years of age.

Exclusion Criteria:

- cognitive impairment as indicated by a score <21 in the Montreal Cognitive Assessment; - presence of other conditions that would substantially influence balance; - an MS relapse or change of disease-modifying treatment within the past 8 weeks

Everyday living means being in complex environments and performing complex activities which usually consist of and require a combination of motor and cognitive skills. Having a neurological disease such as multiple sclerosis (MS) compromises the motor-cognitive performance. This leads to difficulties in balance and gait with or without concurrent performance of cognitive tasks, hindering activity performance and influencing the possibilities for an independent lifestyle. The investigators have, in a co-design process with stakeholders, adapted a HiBalance program, originally developed by the Franzén research group for people with Parkinson's disease and combining motor-cognitive exercises in a progressively more difficult manner (HiBalance-PD), to a program specifically developed to MS (HiBalance-MS). The developed HiBalance-MS program was recently tested and found feasible in a pilot study (results published 2023). The investigators will now perform a randomized controlled trial in people with MS, in order to determine the effects of a highly challenging balance training program (HiBalance-MS) on physical and cognitive functioning, and activity performance, in this group. The results will have immediate application and clinical relevance. With improved balance control people with MS will also gain other health benefits related to an active lifestyle and a better everyday life. The hypothesis that motor-cognitive performance is reduced and impact activity performance in people with MS. They also hypothesize that progressively challenging balance exercise programs that are specific to the balance control domains affected by MS will be effective to improve balance control, walking, motor-cognitive performance, activity performance and health related quality of life. Participants will be recruited through Karolinska University Hospital, through physiotherapists and physicians specialized in neurology in Stockholm and via advertisement in newspapers and the patient organization NEURO Sweden. According to earlier power calculations for detecting effects in balance and gait measures after this particular intervention, the investigators anticipate 40 to 50 participants in each group to detect significant changes. The HiBalance-MS program is based on scientifically well-established principles of exercise training and postural control. It will be conducted as a progressive individually adjusted group training to challenge the specific balance deficit of every participant. Four main sub-systems underlying balance control (stability limits, anticipatory postural adjustments, sensory integration and motor agility) are used to target specific balance impairments. To ensure highly challenging exercises, each task is individually adjusted. Daily variation in capacity will be rated before each training session and participants will at the end of each session rate the challenging level. The training will be performed in the clinic (Karolinska University hospital) for an hour, twice a week for 10 weeks, as a group intervention (6 to 8 participants) facilitated by two physiotherapists/trainers.

Arms

Experimental: Balance training intervention group

The program HiBalance-MS is based on scientifically well-established principles of exercise training and postural control. It will be conducted as a progressive individually adjusted group training to challenge the specific balance deficit of every participant. To ensure highly challenging exercises, each task is individually adjusted, e.g., by altering the base of support, increasing speed, restricting vision and varying grade of multitasking. Daily variation in capacity will be rated before each training session and participants will at the end of each session rate the challenging level. The training will be performed in the clinic, at Karolinska University Hospital, for an hour, twice a week for 10 weeks, as a group intervention including 6 to 8 participants and facilitated by two physiotherapists/trainers.

No Intervention: No intervention control group

Participants in the control group are encouraged to maintain their normal physical activities and are not restricted from participation in ongoing rehabilitation programs.

Interventions

Other: - HiBalance-MS

See arm description for intervention group.