Supplementary Table S1. Type III model tests and robustness summary. Muscle Analysis Attachment p Phase p Attachment × phase p Interpretation Latissimus dorsi Primary 0.063 0.373 0.046 Small interaction in primary model Latissimus dorsi Repetition positions 1 and 2 0.063 0.373 0.046 Similar to primary Latissimus dorsi Complete cases 0.277 0.369 0.075 Interaction attenuated; interpret cautiously Middle trapezius Primary 0.061 < 0.001 0.761 Phase effect retained in sensitivity analyses Middle trapezius Repetition positions 1 and 2 0.106 < 0.001 0.171 Robust Middle trapezius Complete cases 0.266 0.015 0.097 Robust Posterior deltoid Primary 0.003 0.118 0.275 Attachment effect retained in sensitivity analyses Posterior deltoid Repetition positions 1 and 2 0.003 0.086 0.184 Robust Posterior deltoid Complete cases 0.035 0.272 0.445 Robust Biceps brachii Primary < 0.001 < 0.001 < 0.001 Robust attachment, phase, and interaction effects Biceps brachii Repetition positions 1 and 2 < 0.001 < 0.001 < 0.001 Robust Biceps brachii Complete cases < 0.001 < 0.001 < 0.001 Robust Triceps brachii Primary 0.025 0.424 0.412 Attachment effect in primary model Triceps brachii Repetition positions 1 and 2 0.025 0.424 0.412 Similar to primary Triceps brachii Complete cases 0.459 0.279 0.018 Pattern changed; interpret cautiously Values are p values from Type III tests with Satterthwaite approximation. The table summarizes whether the inferential pattern observed in the primary models was preserved in the two sensitivity analyses. This table should be used to interpret robustness across the primary, repetition positions 1 and 2, and complete-case analyses.