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Can you directly compare EMG amp between subjects?

Can you directly compare EMG amp between subjects?. Reproducibility of surface EMG variables and peak torque during three sets of ten dynamic contractions. Barbro Larsson , Bjarne Månsson , Christian Karlberg , Peter Syvertsson , Jessica Elert and Björn Gerdle . Introduction.

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Can you directly compare EMG amp between subjects?

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  1. Can you directly compare EMG amp between subjects?

  2. Reproducibility of surface EMG variables and peak torque during three sets of ten dynamic contractions Barbro Larsson , Bjarne Månsson , Christian Karlberg , Peter Syvertsson , Jessica Elert and Björn Gerdle

  3. Introduction • Isokinetic dynamometers are commonly used for assessment of dynamic muscle strength, endurance and fatigue. • For measurement of reproducibility, intra-class correlation (ICC) is preferred.

  4. Fatigue and EMG • Peripheral muscle fatigue during sustained static contractions is generally characterized by increases in signal energy (RMS or iEMG) and shifts in the EMG spectrum towards lower frequencies (spectral shift). • Fatigue increases amplitude • Fatigue decreases frequency

  5. Problems with Dynamic Contractions and EMG • The interpretation of the EMG from dynamic contractions might be difficult—especially for frequency spectrum variables—because the movement per se introduces additional factors that might affect its characteristics • changes in force throughout the range of motion • changes in fiber and muscle length • movement of the neuromuscular junction with relation to the electrodes position • problems with non-stationary of the signal (recruitment and de-recruitment of MUs

  6. Methods -- Isokinetic • 3 sets of 10 isokinetic contractions at 90 d/s • One hour between sets • The electrodes were NOT REMOVED • ROM was constrained to 90 – 15 deg ext. • Subjects relaxed during knee flexion and the immediately performed extension.

  7. Methods -- EMG • Surface EMG from VL, VM & RF • 20 mm interelectrode distance on center of muscle in line with muscle fibers. • Sampled at 2KHz with 12 bit A/D • EMG band pass filtered at 16-500 Hz • Torque & Position low pass filtered at 40 Hz

  8. EMG Processing & Statistics • FFT with Hamming window (2 Hz resolution) • RMS used for amplitude • Signal-amplitude ratio (SAR) of relaxation (flexion phase) to contraction (extension phase). • ICC (3,1) Shrout & Fleiss • One-way ANOVA was used to test for differences between sets.

  9. Results • No significant differences between the three sets. • Peak torque had high reproducibility (0.99) • Rectus femoris generally had lower ICC than the two other muscles • RMS generally had somewhat higher ICC than the MNF

  10. Discussion • High ICC may be due to limited ROM which may control movement effects. • Previous studies have reported good reproducibility for during and between day static contractions. • Not REMOVING ELECTRODES may have contributed to high ICC

  11. Discussion -- Cont • We have reported that the MNF correspond to physiological properties during dynamic contractions • Positive significant correlations have been reported between the proportion of Type-II muscle fibers and MNF during single dynamic (non-fatiguing) contractions

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