Near infrared spectroscopy of human muscles
Optical spectroscopy is a powerful tool in research and industrial applications. Its properties of being rapid, non-invasive
and not destructive make it a promising technique for qualitative as well as quantitative analysis in medicine. Recent
advances in materials and fabrication techniques provided portable, performant, sensing spectrometers readily operated
by user-friendly cabled or wireless systems. We used such a system to test whether infrared spectroscopy techniques,
currently utilized in many areas as primary/secondary raw materials sector, cultural heritage, agricultural/food industry,
environmental remote and proximal sensing, pharmaceutical industry, etc., could be applied in living humans to
categorize muscles. We acquired muscles infrared spectra in the Vis-SWIR regions (350-2500 nm), utilizing an ASD
FieldSpec 4™ Standard-Res Spectroradiometer with a spectral sampling capability of 1.4 nm at 350-1000 nm and 1.1
nm at 1001-2500 nm. After a preliminary spectra pre-processing (i.e. signal scattering reduction), Principal Component
Analysis (PCA) was applied to identify similar spectral features presence and to realize their further grouping. Partial
Least-Squares Discriminant Analysis (PLS-DA) was utilized to implement discrimination/prediction models. We studied
22 healthy subjects (age 25-89 years, 11 females), by acquiring Vis-SWIR spectra from the upper limb muscles (i.e.
biceps, a forearm flexor, and triceps, a forearm extensor). Spectroscopy was performed in fixed limb postures (elbow
angle approximately 90°). We found that optical spectroscopy can be applied to study human tissues in vivo. Vis-SWIR
spectra acquired from the arm detect muscles, distinguish flexors from extensors.