L_x (left) and L_x∕L_bol (right) vs. rotation period for stars with direct rotation period determination. The black squares correspond to the stellar sample from Pizzolato et al. (2003) in the mass range 0.22 < M∕M_⊙ < 0.60. The blue and red dots correspond to the M dwarfs from this work in the two different ranges of T_eff indicated inthe legend. The black dot-dashed line represents the broken power law obtained by the fitting procedure from Pizzolato et al. (2003). The blue and red solid line represents our best fit for the 3400–3700 and 3700–3900 K T_eff range, respectively.