Theoretical near-infrared M-dwarf synthetic spectra and corresponding LSD profiles. Left panels: disk-centre Stokes I spectra computed for a model atmosphere with T_eff = 3500 K and log g = 5.0, both with (red) and without (black) molecular line opacity. A 100 G line-of-sight magnetic field was adopted for these calculations. Blue bars above the spectra mark the positions of atomic lines included in the LSD mask, with bar lengths proportional to their central depths. Grey rectangles highlight wavelength regions excluded from the analysis because they are heavily contaminated by telluric absorption in typical ground-based observations. Right panels: Corresponding LSD profiles: Stokes I (upper) and Stokes V (lower).