Supplementary Table S2. Sample audit for the primary and sensitivity analysis datasets. Analysis Muscle Analytical-interval observations Participants Primary Latissimus dorsi 174 13 Primary Middle trapezius 171 13 Primary Posterior deltoid 181 14 Primary Biceps brachii 171 13 Primary Triceps brachii 178 14 Repetition positions 1 and 2 Latissimus dorsi 174 13 Repetition positions 1 and 2 Middle trapezius 169 13 Repetition positions 1 and 2 Posterior deltoid 179 14 Repetition positions 1 and 2 Biceps brachii 171 13 Repetition positions 1 and 2 Triceps brachii 178 14 Complete cases Latissimus dorsi 109 7 Complete cases Middle trapezius 110 7 Complete cases Posterior deltoid 123 8 Complete cases Biceps brachii 124 8 Complete cases Triceps brachii 94 6 Analytical-interval observations refer to the number of lifting or lowering sEMG observations entering each model. The complete-case analysis reflects a stricter subset requiring complete observations for all 4 attachment × 2 phase combinations within each muscle.