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