Table 1.

Methodological steps COSMIN^a

Methodological steps	Questions to be answered	Sources
Step 1: Definition and elaboration of the construct	1) Definition of fatigability? 2) Target population? 3) Purpose of the outcome measure?	• Key papers on fatigability assessment
Step 2: Choice of measurement method	1) Existing measurement that responds closely to construct to be measured? 2) Level of measurement? 3) Single or multiple measures?	• Scoping review of scientific literature • Expert panel (round table discussion 1)
Step 3: Selecting and formulating items	1) Which activities cause most problems? 2) Which available measures reflect these activities?	• Patient report outcome (pilot sample 3) • Expert panel (round table discussion 2)
Step 4: Scoring issues	1) Application in research or clinical practice? 2) Measurement level?	• Expert panel (round table discussion 3)
Step 5: Pilot testing	1) Comprehensibility? 2) Feasibility? 3) Relevance?	• Pilot sample 1 (healthy subjects) • Pilot sample 2 (pediatric patients with chronic diseases) • Pilot sample 3 (patients with SMA)

^aCOSMIN = ‘COnsensus-based Standards for the selection of health Measurement Instruments