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1/n Surface EMG & tea-leaves...
sEMG is influenced by RFD... so we need to be careful in interpreting differences in sEMG between fast and slower contractions. High RFD's may make muscles appear more 'activated' than they are...
https://www.researchgate.net/publication/8086961_Effects_of_Rate_of_Force_Development_on_EMG_Amplitude_and_Frequency
sEMG is influenced by RFD... so we need to be careful in interpreting differences in sEMG between fast and slower contractions. High RFD's may make muscles appear more 'activated' than they are...
https://www.researchgate.net/publication/8086961_Effects_of_Rate_of_Force_Development_on_EMG_Amplitude_and_Frequency
2/n ...or at least make the comparison pointless. See also https://www.frontiersin.org/articles/10.3389/fphys.2017.00985/full for some further limitations of the sEMG signal
3/n Despite normalisation to a completely arbitrary MVC, we can't evaluate the degree of activation between exercises accurately because they typically involve different joint angles & muscle lengths & both change the amount of muscle directly underneath the recording electrodes
4/n We also see sEMG studies in which exercises of different intensities are compared. eg Deadlifts without external loads (toe touches) v Nordics and surprise surprise the supramaximal exercise gives higher hamstring sEMG!
5/n The idea of predicting adaptations from sEMG is fanciful (see paper in 2nd tweet in this thread) because all the important mechanical factors (muscle length, force) involved in exercise are ignored.
6/n Slight side-tracking here but in some circumstances T2 changes w/ fMRI results may predict adaptation... but there are significant limitations (relative not absolute levels of hypertrophy seem to match relative acute T2 changes in different exercises) https://pubmed.ncbi.nlm.nih.gov/29116573/
7/n But if you like sEMG it can, like tea-leaves, be interpreted the way that you like. There is a sEMG study for almost every conclusion you've already made...
