A Wireless Multi-Layered EMG/MMG/NIRS Sensor for Muscular Activity Evaluation

Abstract

A wireless multi-layered sensor that allows electromyography (EMG), mechanomyography (MMG) and near-infrared spectroscopy (NIRS) measurements to be carried out simultaneously is presented. The multi-layered sensor comprises a thin silver electrode, transparent piezo-film and photosensor. EMG and MMG measurements are performed using the electrode and piezo-film, respectively. NIRS measurements are performed using the photosensor. Muscular activity is then analyzed in detail using the three types of data obtained. In experiments, the EMG, MMG and NIRS signals were measured for isometric ramp contraction at the forearm and cycling exercise of the lateral vastus muscle with stepped increments of the load using the layered sensor. The results showed that it was possible to perform simultaneous EMG, MMG and NIRS measurements at a local position using the proposed sensor. It is suggested that the proposed sensor has the potential to evaluate muscular activity during exercise, although the detection of the anaerobic threshold has not been clearly addressed.

Keywords: electromyography; layered sensor; mechanomyography; near-infrared spectroscopy; wireless.

Figure 1

Multi-layered sensor: (a) schematic diagrams of the sensor and (b) photographs of sensors.

Figure 2

Schematic diagram of the measurement system for EMG, MMG and NIRS and changes in concentrations of oxyhemoglobin (HbO₂) and deoxyhemoglobin (Hb) are obtained through NIRS using LED and PD, respectively. EMG, MMG and NIRS are thus measured simultaneously by a pair of sensors.

Figure 3

Wireless multi-layered sensor: (a) photograph of the device and (b) schematic diagram of the signal processing system.

Figure 4

Schematic diagram of the experimental method: (a) isometric ramp contraction at the forearm and (b) cycling exercise of the lateral vastus muscle with step increments of the load.

Figure 5

Experimental results for isometric ramp contraction: (a) EMG, (b) MMG (LED), (c) MMG (PD) and (d) NIRS.

Figure 6

Experimental results for isometric ramp contraction: (a) EMG, (b) MMG (LED), (c) MMG (PD) and (d) NIRS.

Figure 7

ΔHb/EMG in isometric ramp contraction.

Figure 8

Experimental results for isometric ramp contraction: (a) EMG, (b) MMG (LED), (c) MMG (PD) and (d) NIRS.

Figure 9

Comparison of the timings of the AT obtained from ΔHb/EMG and relationship between VO2 and VCO2 in cycling exercise: (a) ΔHb/V_EMG and (b) relationship between VO2 and VCO2.