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  • Title: Global electromyographic signal characteristics depend on maximal isometric contraction method in the knee extensors.
    Author: Tomko PM, Colquhoun RJ, Magrini MA, Muddle TWD, Jenkins NDM.
    Journal: J Electromyogr Kinesiol; 2018 Oct; 42():111-116. PubMed ID: 30015134.
    Abstract:
    OBJECTIVE: To determine if maximal isometric contraction (MVIC) method (i.e., ramp (MVICRAMP) versus traditional MVIC) influences (1) maximal voluntary isometric torque (MVIT) production of the knee extensors, (2) electromyographic signal amplitude (EMGAMP), and (3) EMG mean power frequency (EMGMPF) of the rectus femoris and vastus lateralis in moderately-to highly-activated subjects. We hypothesized that EMGAMP would be greater during the MVICRAMP than MVIC muscle contractions, but that there would be no difference in MVIT. APPROACH: Twenty-five males (23.4 ± 3.4 y; % voluntary activation = 93.9 ± 5.1%) visited the laboratory and completed MVICRAMPs and MVICs. During all contractions, leg extensor torque and sEMG signals from the vastus lateralis (VL) and rectus femoris (RF) were recorded. MAIN RESULTS: There was no significant difference in the MVIT produced (p = 0.65) or in EMGMPF (p = 0.052) during MVICRAMP versus MVIC. However, EMGAMP was 18.1% higher during the MVICRAMP than MVIC (p = 0.004). SIGNIFICANCE: Maximal isometric muscle contraction method significantly influenced EMGAMP, and had a moderate effect on EMGMPF (d = 0.49). Investigators who utilize MVICs to determine maximal EMG signal amplitude and frequency to normalize their EMG signals should be aware of these differences.
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