Psychometric Properties of a Clinical Strength Assessment Protocol in People with Multiple Sclerosis

Abstract

Background: Strength training in people with multiple sclerosis (MS) is an important component of rehabilitation, but it can be challenging for clinicians to quantify strength accurately and reliably. This study investigated the psychometric properties of a clinical strength assessment protocol using handheld dynamometry and other objective, quantifiable tests for the lower extremities and trunk in people with MS. Methods: This study determined discriminant validity between 25 participants with MS and 25 controls and between participants with MS who had higher versus lower disability; test-retest reliability across 7 to 10 days; and response stability. The protocol included handheld dynamometry measurements of ankle dorsiflexion, knee flexion and extension; hip flexion, extension, abduction, and adduction; and trunk lateral flexion. Muscular endurance tests were used to measure trunk extension, trunk flexion, and ankle plantarflexion. Results: The protocol discriminated between participants with MS and controls for all muscles tested (P < .001–.003). The protocol also discriminated between low- and moderate-disability groups (P = .001–.046) for 80% of the muscles tested. Test-retest reliability intraclass correlation coefficients were high (0.81–0.97). Minimal detectable change as a percentage of the mean was 13% to 36% for 85% of muscles tested. Conclusions: This study provides evidence for the discriminant validity, test-retest reliability, and response stability of a strength assessment protocol in people with MS. This protocol may be useful for tracking outcomes in people with MS for clinical investigations and practice.