Noninvasive techniques, surface electromyography (sEMG) in particular, are being increasingly employed for assessing muscle activity. In these studies, local oxygen consumption and muscle metabolism are of great interest. Measurements can be performed noninvasively using optics-based methods such as near-infrared spectroscopy (NIRS). By combining energy consumption data provided by NIRS with muscle level activation data from sEMG, we may gain an insight into the metabolic and functional characteristics of muscle tissue. However, muscle motion may induce artifacts into EMG and NIRS. Thus, the inclusion of simultaneous motion measurements using accelerometers (ACMs) enhances possibilities to perceive the effects of motion on NIRS and EMG signals. This paper reviews the current state of noninvasive EMG and NIRS-based methods used to study muscle function. In addition, we built a combined sEMG/NIRS/ACM sensor to perform simultaneous measurements for static and dynamic exercises of a biceps brachii muscle. Further, we discuss the effect of muscle motion in response of NIRS and EMG when measured noninvasively. Based on our preliminary studies, both NIRS and EMG supply specific information on muscle activation, but their signal responses also showed similarities with acceleration signals which, in this case, were supposed to be solely sensitive to motions.
Kauppi, K., Korhonen, V., Ferdinando, H., Kallio, M., & Myllylä, T. (2017). Combined surface electromyography, near-infrared spectroscopy and acceleration recordings of muscle contraction: The effect of motion. Journal of Innovative Optical Health Sciences, 10(2). https://doi.org/10.1142/S1793545816500565