 To set the estimated number of participants a two-sample two-sided power calculation has been conducted. The basis for this calculation is an report from Tallner et al. who have shown a difference in relapse rate during a two-year period equal to our 1 year intervention, and 1 year follow-up of 0.65 relapses between physically active and physically inactive MS patients active: 0.95 - 0.97 relapses in 2 years ; inactive: 1.60 - 1.64 relapses in 2 years. 83 patients with MS should be enrolled in each intervention group a 20 drop-out rate has been included. Newly published data on the brain atrophy in percentage of total brain volume after 24 weeks of resistance training have been the basis for a similar calculation of the number of participants in the sub-group, from whom MRI-scans and blood samples will be obtained. 41 participants from each intervention group should form this sub-group. 