L_x (left) and L_x∕L_bol (right) vs. rotation period. The black squares correspond to the stellar sample from Pizzolato et al. (2003) in the mass range 0.22 <M∕M_⊙ < 0.60. The large blue dots correspond to the M dwarfs with periods measured from time series and used in the analysis. The open blue circles show the derived period from an activity–rotation relation (excluded from the analysis). The black dot-dashed line represents the broken power law obtained by the fitting procedure from Pizzolato et al. (2003) with P_rot values estimated from vsini in saturated regime.