Influence of Electrode Configuration on Muscle-Fiber-Conduction-Velocity Estimation Using Surface Electromyography

Objective:
Muscle fiber conduction velocity (MFCV) is an important myoelectric parameter and can be estimated by analysing surface electromyography (EMG). Among many factors, electrode configuration plays a key role on MFCV estimation. Most studies adopt bipolar configuration (BC) for CV estimation. However, a thorough understanding of the underlying mechanism is lacking, confusing the design of the most appropriate EMG measurement setup for CV estimation. The aim of this study is therefore to systematically investigate the influence of electrode configuration on MFCV estimation.
Methods:
Four possible configurations are considered, including BC, monopolar configuration (MC), common average reference (CAR), and a special monopolar configuration (SMC) using a fixed channel on the active muscle as reference. For each configuration, mathematical models computing the time delay between adjacent channels are derived and evaluated by dedicated simulation as well as real EMG measurements. MFCV was calculated using the maximum likelihood algorithm with and without channel normalization.
Results:
The simulation results are in line with the mathematical models. The CVs estimated from the real EMG with and without normalization are 4.3
$\pm$
0.7 and 7.2
$\pm$
3.7 m/s, 5.7
$\pm$
1.3 and 20.4
$\pm$
4.7 m/s, 9.0
$\pm$
3.4 and 20.6
$\pm$
9.8 m/s, and 5.5
$\pm$
2.5 and 5.5
$\pm$
2.4 m/s for BC, MC, SMC, and CAR, respectively.
Conclusion:
Our results show normalized BC to produce the most accurate CV estimation, in line with the mathematical models and the simulation results.
Significance:
These findings enable a better understanding of the influence of electrode configuration on MFCV estimation, providing useful information for EMG measurement setup design aiming at MFCV studies.