# NIRS-EMG for Clinical Applications: A Systematic Review
## 4 NIRS-EMG: Review of Studies in Clinical Practice
### NIRS and EMG  
In this section, we only present the works in which both NIRS and EMG signals were acquired at the same time and where an interpretation, from a physiological point of view, was given to both the signals. In Table 1, a list of the nine works found is reported. In this table, for each work, we have summarized: The number of patients and controls involved, the aim of the study, the target muscles, the experimental protocol, and the NIRS and EMG parameters extrapolated. Most of them focused on the understanding of the metabolic and fatigue mechanisms in patients with muscular pain. Furthermore, we added (in squared brackets) a classification label for these works, based on their field of application. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  
The first work on patients with chronic lower back pain (CLBP) was that of [PERSON] et al., dated 2005 [67]. Their aim was to compare the paraspinal muscle oxygenation and muscle function characteristics (activation level and fatigue) between CLBP patients (n = 17) and healthy controls (n = 12). Furthermore, they studied the effects of subcutaneous tissue thickness on NIRS and EMG measurements. The paraspinal muscle NIRS oxygenation and EMG fatigability results, during a dynamic back endurance test, did not differ between the groups. This indicates that the oxygen consumption and endurance capacity was similar in the CLBP and healthy control groups. It was shown that the subcutaneous tissue thickness over the lumbar paraspinal muscles strongly influenced the NIRS and EMG amplitude measurements; for this reason, it should be incorporated in the statistical analysis as confounding factor. More recently, in 2017, [PERSON] et al. investigated patients with LBP (n = 273), after a decompression surgery, for lower extremity symptoms in lumbar spinal stenosis (LSS) [68]. The patients were, then, divided into three groups: Walking-induced, LBP that was aggravated during walking (W group); motion-induced, LBP that was aggravated during sitting (M group); and no LBP (N group). In particular, they wanted to identify the features of motion-induced and walking-induced LBP in patients with LSS and to assess whether neuropathic LBP had developed. The electrodes and optodes were placed on the lumbar multifidus muscle during extension of the lumbar spine. In the hemodynamic evaluation, the oxygenated hemoglobin level was significantly lower in the W group than in the M and N groups. In an electrophysiological evaluation of lumbar multifidus, the mean power frequency from the EMG signal was significantly higher in the W group than in the N group. These results suggest that neurologic disturbance in patients with LSS may be attributed to \"neuropathatic LBP\". They concluded that neuropathic multifidus disorder could play a role in walking-induced LBP. When considering muscular pain, we cite two works from [PERSON] et al., one published in 2013 [69] and one in 2014 [70], where patients with neck-shoulder-arm pain (n = 18) were considered together with control subjects (n = 17). Extensor carpi radialis (ECR) and trapezius descendens (TD) were both