# NIRS-EMG for Clinical Applications: A Systematic Review
## 4 NIRS-EMG: Review of Studies in Clinical Practice
### NIRS and EMG
From the NIRS signal, it was shown that the females with work-related neck-shoulder complaints had muscle metabolic insufficiencies at rest and during standardized repetitive and stress tasks, similar to those among chronic neck-shoulder pain patients. [PERSON] et al. published a work, in 2012, presenting the results during the same protocols and on the same subjects, after 10 weeks of training [72]. The subjects underwent general fitness training, performed by leg-bicycling (GFT) or specific strength training for the neck/shoulder muscles (SST). GFT improved trapezius oxygenation, decreasing pain development during repetitive work tasks. SST lowered the relative EMG amplitude (i.e., the overall level of pain) both during rest and work. These results show a differential adaptive mechanism of contrasting physical exercise interventions on chronic muscle pain at rest and during repetitive work tasks. A completely different NIRS-EMG application was presented by [PERSON] et al. [73] and [PERSON] et al. [74]. They evaluated the effects of passive leg movements on muscle oxygenation levels and electromyographic activity in the lower limbs of 15 chronic stroke patients. Passive leg movement was achieved by means of a gait apparatus, where patients trained on for 10 min. EMG and NIRS probes were placed distally and proximally on the medial side of gastrocnemius muscle; EMG probes were also placed on the soleus muscle. The EMG signal was evaluated only in terms of amplitude and was useful in the comparison of muscular activity between the two muscle types and between paretic and non-paretic muscles. In particular, in patients with good motor recovery, the MVC level of the paretic calf muscle was higher than in the poor recovery subgroup, but there was no difference in the EMG activity induced by passive movement. These results, therefore, suggest that passive movement could induce EMG activity in the paretic muscle, regardless of its voluntary contraction capacity. Concerning the NIRS findings, they affirmed that the muscle oxygenation levels of both paretic and non-paretic calf muscles could be enhanced by imposing passive leg motion. The effects of passive movements varied in accordance with the motor recovery level. This type of exercise may be a useful and efficient method for prevention of muscle metabolic deterioration and bring forth new perspectives in clinical rehabilitation settings. The most recent work which employed both NIRS and EMG on patients was from [PERSON] et al., published in 2018 [75]. They focused on 20 patients scheduled for an arthroscopic anterior cruciate ligament (ACL) reconstruction with ipsilateral hamstring autograph ACL reconstruction. They investigated the vastus medialis and lateralis muscle, respectively, with NIRS and EMG techniques during sustained isometric contraction at 30% of maximal voluntary isometric contraction (MVIC) performed to volitional failure. Patients were assigned into either a blood flow restricted (BFR) group, performing a low-load BFR knee-extension exercise, or a SHAM-BFR group, replicating equal training volume during a sham occlusion. Measurements were carried out prior to the intervention and again 4 and 12 weeks after surgery. From the analysis of the RMS, amplitude, and median frequency of the EMG and blood flow consideration coming from the NIRS signal, they could affirm that patientstreated with the low-load BFR exercise protocol did not display deterioration in quadricep muscle endurance in the first 4 weeks after surgery; whereas patients who had performed the same exercise protocol with sham occlusion demonstrated an approximate 50% reduction in muscle endurance. This difference in endurance between groups was no longer evident at 12 weeks post-surgery and, thus, the main hypothesis was only partially confirmed. Finally, we found also a recent work about the evaluation of the skeletal muscle function during rehabilitation after acute heart failure, which was only a design study; namely, no data from patients has yet been acquired [76].