Background: Periodizing exercise interventions in Multiple Sclerosis (MS) shows good high intensity exercise training adherence. Whether this approach induces comparable training adaptations with respect to exercise capacity, body composition and muscle strength compared to conventional, linear progressive training programs however is not known. Methods: Thirty-one persons with MS (all phenotypes, mean EDSS 2.3?1.3) were randomized into a twelve-week periodized (MSPER, n=17) or a classic endurance (MSCLA, n=14) training program. At baseline (PRE), exercise capacity (maximal exercise test, VO2max), body composition (DEXA) and muscle strength (Biodex?) were assessed. Classic, moderate intensity endurance training (60-80% HRmax, 5 training sessions/2w, 60min/session) was performed on a stationary bicycle. Periodized exercise included 4 recurrent 3-week cycles of alternated endurance training (week 1: endurance training as described above), high intense exercise (week 2: 3 sessions/w, 3 ? 20s all-out sprints, 10min/session) and recovery weeks (week 3: one sprint session as described above). POST measurements were performed similar to baseline. Total exercise volume of both programs was expressed as total peak-effort training minutes. Results: For MSCLA, total exercise volume included 1728 total peak-effort training minutes, whereas MSPER included only 736. Despite this substantially reduced training volume, twelve weeks of periodized training significantly (p
