X-ray activity vs mass for the validated samples (see legend in Figs. 7 and 8) restricted to the saturated stars, i.e., stars with P_rot ≤ 8.5 d, best fit (violet) and median plus standard deviation of the data (red) in bins of 0.1 M_⊙. The fit to the young stars in the Orion Nebular cluster provided by (Preibisch et al. 2005) is also shown, together with the standard deviation of this fit (green) and the best fit we found for the full M dwarf sample presented in the top panels of Fig. 7 (cyan). Left: X-ray luminosity vs. mass. Right: X-ray over bolometric luminosity vs. mass.