BackgroundIt is unknown how impairments caused by multiple sclerosis (MS) affect upper limb capacity, performance, and community integration.ObjectiveThe aim of this study was to investigate the extent to which impairments explained the variance in activity level and participation level measures of the International Classification of Functioning, Disability and Health (ICF) and the extent to which upper limb capacity measures explained perceived performance on the activity level in people with MS and different dexterity levels.DesignThis was a cross-sectional study.MethodsA total of 105 people with MS (median Expanded Disability Status Scale=6.5) were assessed with measures on the ICF body functions and structures level (strength, active range of motion of the wrist, tactile sensitivity, tremor, spasticity, and pain), activity level (Nine-Hole Peg Test [NHPT], Action Research Arm Test, and Manual Ability Measure-36 [MAM-36]), and participation level (Community Integration Questionnaire). The sample was divided into low- and high-dexterity subgroups on the basis of the median score on the NHPT.ResultsIn the total group, muscle strength, tactile sensitivity of the thumb, and intention tremor explained 53% to 64% of the variance in activity level measures. In the low-dexterity subgroup, muscle strength and active range of motion explained 43% to 71% of the variance in activity level measures. In the high-dexterity subgroup, only 35% of the variance in the MAM-36 was explained by muscle strength. Capacity measures (NHPT and Action Research Arm Test) were moderately to highly associated with perceived performance (MAM-36) in the low-dexterity subgroup.LimitationsSome outcome measures showed ceiling effects in people with MS and a high dexterity level.ConclusionsUpper limb muscle strength is the most important impairment affecting capacity and perceived performance in daily life. Associations among outcome measures differ in people with MS and different dexterity levels.