A methodological reinterpretation of quadriceps EMG amplitude to torque ratios across knee angles using archived data

Abstract Ratios of surface electromyographic (sEMG) amplitude to torque cannot establish neural efficiency. This secondary analysis provides a methodological reinterpretation of previously published ratio findings from 17 participants (11 men, 6 women). Two 3-s maximal isometric knee-extension contractions were performed at each of 45° and 75° knee flexion. Biodex average peak torque and archived Noraxon mean-amplitude outputs were examined separately. The paired torque difference (45° minus 75°) was − 94.8 N·m (bias-corrected and accelerated [BCa] 95% confidence interval − 126.9 to − 69.8). Corresponding differences were − 21.9 µV (− 94.4 to 91.2) for vastus lateralis and − 48.1 µV (− 139.7 to 4.5) for vastus medialis. These uncertain EMG estimates do not establish equivalence between angles. Rectus femoris was restricted to exploratory supplementary reporting because hip angle was undocumented. The lower archived torque output illustrates why a higher ratio need not imply greater electrical amplitude, but does not quantify the contributions to the ratio change. Findings are specific to this archived dataset and experimental protocol. Incomplete EMG-processing metadata introduce uncertainty in the magnitude of between-angle EMG differences beyond the reported intervals. Together with absent gravity correction and inability to evaluate fatigue, these limitations preclude attribution to a specific physiological mechanism.