The Relationship Between Skinfold Thicknesses and Mechanomyography At Different Locations on the Vastus Lateralis During Incremental Cycle Ergometry

Abstract

Previous studies have indicated that skinfold thickness (SKF) acts as a low-pass filter to the mechanomyographic (MMG) signal. PURPOSE: The purpose of this study was to examine the effects of SKF at four different locations on the vastus lateralis (VL) muscle on MMG amplitude and mean power frequency (MPF) responses during incremental cycle ergometry. METHODS: Twenty adults (age ± SD = 23.8 ± 3.0 years) volunteered to participate in the investigation. An orientation session was performed to determine the location of the innervation zone (IZ) for the VL using a linear electrode array. The MMG signals from the VL muscle were detected during an incremental cycle ergometry test using four accelerometers placed on the right VL proximal (Prox1), over (Over IZ), and distal (Dist IZ) to the IZ. A fourth accelerometer was placed at the site recommended by the SENIAM Project (Prox2) for the placement of EMG electrodes. Prior to the test, three SKF were taken at each accelerometer placement site. The mean of the three SKF at each site were used for the analysis. The subjects were divided (at the median SKF value) into two groups of smaller (n = 10) and larger (n = 10) SKF values. Simple linear regression analyses were performed for SKF vs. MMG amplitude and MPF at each location for power outputs of 50, 75, 100, 125, 150, and 175W. Independent t-tests were also performed between the smaller and larger SKF groups for SKF measurements, MMG amplitude, and MMG MPF values at each accelerometer placement site. An alpha of p ≤ 0.05 was considered statistically significant for all analyses. RESULTS: For the 48 regression analyses, there were only 2 significant relationships (r = −0.461 and −0.519) between the SKF values and MMG MPF and 3 significant relationships between the SKF values and MMG amplitude (r = −0.535, −0.456, and −0.443). The independent t-tests showed that there were significant mean differences between the smaller and larger SKF groups for SKF measurements for all accelerometer placements sites. Of the 48 mean comparisons, only 1 was significantly different between the smaller and larger SKF groups for MMG MPF and 4 for MMG amplitude. CONCLUSIONS: The present study showed that, in general, SKF values were not correlated with the MMG signal. Only 10% of the regression analyses for SKF versus MMG MPF and MMG amplitude were statistically significant. In addition, only 10% of the mean comparisons between smaller and larger SKF groups for MMG MPF and MMG amplitude were significantly different. Thus, the results of the present study indicated that the larger SKF values did not attenuated the MMG signal. Other factors, including changes in force production and muscle length, as well as factors related to the accelerometer location, such as amount of muscle mass, muscle architecture, and/or motor unit territorial distribution may have had a greater effect on the MMG signal than SKF. PRACTICAL APPLICATIONS: These findings indicated that, in generall, smaller and larger SKF values did not correlate with the amplitude and frequency parameters of the MMG signal. Thus, there may be other anatomical, physiological, or methodological factors that have a greater effect on the MMG signal. These findings provide information about a methodological consideration necessary for the interpretation of the MMG signal.