Effects of pennation angle,electrodes orientation and knee angle on surface electromyography of vastus lateralis during isometric contractions

Purpose

The effects of pennation angle (PA), electrode orientation (EO) and knee angle (KA) on the amplitude of electromyography signal (EMG) of vastus lateralis muscle (VL) were investigated.

Methods

Seventeen participants (8 men and 9 women; 26.5 ± 5.1 years; 64.4 ± 12.3 kg; 1.66 ± 0.09 m) accomplished isometric tests at four contraction intensities (COI): 25, 50, 75 and 100% of maximum voluntary contraction (MVC), with KA at 90° and 120°. PA was measured at rest and during contractions. One pair of electrodes was aligned with PA of relaxed VL fibers (pair 1) and another (pair 2) was 20° internally rotated to pair 1. The EMG root mean square (RMS) was calculated and later corrected (RMS_C) using equations including PA and 20° angle.

Results

PA increased with COI (p < 0.001), but was not influenced by KA. Both RMS and RMS_C were higher with KA at 90° than 120° (p < 0.01). RMS, but not RMS_C were higher from pair 1 in COI at 50 and 75% MVC (p < 0.05). Correlations between outcomes obtained with pair 1 and pair 2 were stronger for RMS_C (r = 0.99; p < 0.001) than RMS (r = 0.93; p < 0.01). No effect of KA or COI was detected for RMS or RMS_C expressed as %MVC (p > 0.05).

Conclusion

The PA can be used to improve RMS estimation and further expressed as %MVC maybe promisor in EMG–force related issues. Association between EMG and PA appears to be dependent on their relation to COI.