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) versus traditional MVIC) influences (1) maximal voluntary isometric torque (MVIT) production of the knee extensors, (2) electromyographic signal amplitude (EMG), and (3) EMG mean power frequency (EMG) of the rectus femoris and vastus lateralis in moderately-to highly-activated subjects. We hypothesized that EMG would be greater during the MVIC 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 MVICs 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 (p = 0.052) during MVIC versus MVIC. However, EMG was 18.1% higher during the MVIC than MVIC (p = 0.004).

SIGNIFICANCE

Maximal isometric muscle contraction method significantly influenced EMG, and had a moderate effect on EMG (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.