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

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.

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.

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).

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.