Global electromyographic signal characteristics depend on maximal isometric contraction method in the knee extensors

Objective: To determine if maximal isometric contraction (MVIC) method (i.e., ramp (MVIC_RAMP) versus traditional MVIC) influences (1) maximal voluntary isometric torque (MVIT) production of the knee extensors, (2) electromyographic signal amplitude (EMG_AMP), and (3) EMG mean power frequency (EMG_MPF) of the rectus femoris and vastus lateralis in moderately-to highly-activated subjects. We hypothesized that EMG_AMP would be greater during the MVIC_RAMP 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 MVIC_RAMPs 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 EMG_MPF (p = 0.052) during MVIC_RAMP versus MVIC. However, EMG_AMP was 18.1% higher during the MVIC_RAMP than MVIC (p = 0.004).

Significance: Maximal isometric muscle contraction method significantly influenced EMG_AMP, and had a moderate effect on EMG_MPF (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.