Shoulder strength in adults with and without shoulder pain: preregistered analysis plan for an observational cross-sectional study

Preregistration of the analysis plan for an observational cross-sectional study comparing shoulder strength between adults with and without shoulder pain (SPADI > 20 versus ≤ 20; n = 87, 37 with pain and 50 without). Strength was measured with a functional electromechanical dynamometer (MyoQuality M1) in six movements, isometric and isokinetic (concentric and eccentric), in both arms. The primary outcomes are 18 peak-force variables analysed on the log scale with linear mixed models adjusted for age, sex and body mass, a graphical multiple-testing procedure and relevance thresholds (smallest worthwhile change) computed in the control group. All data were collected before registration; the plan was fixed before any comparison of strength outcomes between groups, and the document declares every inspection of the data made beforehand. Version 1.0, plan ratified on 29 September 2026.