Changes in the electromyographic spectrum power distribution caused by a progressive increase in the force level

Abstract

The purpose of the present study was to determine the specific changes occurring in the power spectrum with an increasing force level during isometric contractions. Surface electromyographic signals of the triceps brachii (TB) and the anconeus (AN) of 29 normal subjects were recorded during isometric ramp contractions performed from 0 to 100% of the maximum voluntary contraction (MVC) in a 5-s period. Power spectra were obtained at 10, 20, 30, 40, 50, 60, 70, 80 and 90% MVC. Changes in the shape of these spectra were evaluated visually and with the calculation of several statistical parameters related to the distribution of power along the frequency axis, such as median frequency and mean power frequency, standard deviation, skewness, first and third quartiles and half-power range. For the AN, the behaviour of the spectrum was relatively similar across subjects, presenting a shift toward higher frequencies without any major change in the shape of the spectrum. For the TB, subjects with a thin skinfold thickness presented similar behaviours. In subjects with a thicker skinfold, however, a loss of power in the high frequency region paralleled the increase in the force level. Significant correlations were obtained between the extent of the change in the value of higher order statistical parameters across force and the thickness of the skin. This points out the importance of the skinfold layer when recording with surface electrodes. Furthermore, the use of a combination of several parameters appears to provide a better appreciation of the changes occurring in the spectrum than any single parameter taken alone.

A Study of the Influence of Muscle Type and Muscle Force Level on Individual Frequency Bands of the EMG Power Spectrum

“…A similar tendency could be seen for the C11 parameter which also defines the band of high frequencies (~270-500 Hz) in the EMG power spectrum. These relationships are consistent with Bilodeau, Cincera, Gervais, et al's [27] conclusions, who reported that for the triceps brachii muscle there was a decrease in the power spectrum at high frequencies together ED S16 S13-S16 -PL S15, S16 S4, S15, S16 -…”

Knee extensor torque, work, and EMG during subjectively graded dynamic contractions

“…In the absence of significant muscle fatigue developing during each contraction, the present analysis of EMG activity reflects the relative activation of the muscle; therefore, any genderspecific pattern in torque production would mani- fest a similar response in EMG activity. Although gender differences in EMG signal (frequency content) have been observed previously, 4,6,37,39 the dynamic nature of the contractions in the present study would have likely yielded nonstationary signals, 47 confounding traditional frequency spectrum analyses.…”

The effects of voluntary contraction effort on quadriceps femoris electromyogram median frequency in humans: a muscle and sex comparison

“…As mentioned, the scientific literature has revealed some inconsistent findings regarding the effects of the level of intensity of contraction on the f med of the EMG. Some investigations have shown a negligible effect of the level of muscle force on the EMG f med for the triceps brachii (Bilodeau et al 1995), biceps brachii (Hagberg and Ericson 1982), muscles of the forearm (Petrofsky and Lind 1980), and the VM and RF muscles (Pincivero et al 2001). It appears, however, that certain muscles generate spectrum parameters of the EMG (i.e.…”

“…The f med refers to the frequency in the sampled EMG bandwidth that divides the power spectrum into halves (Bilodeau et al 1995), and is considered to reflect the conduction velocity of the action potential of the muscle fiber (Kupa et al 1995). As mentioned, the scientific literature has revealed some inconsistent findings regarding the effects of the level of intensity of contraction on the f med of the EMG.…”