  We report our results on how to obtain the Regge trajectory of a resonance
from its pole in a scattering process by imposing analytic constraints in the
complex angular momentum plane. The method, suited for resonances that dominate
an elastic scattering amplitude, has been applied to the {\rho}(770) and the
f_0(500) resonances. Whereas for the former we obtain a linear Regge
trajectory, characteristic of ordinary quark-antiquark states, for the latter
we find a non-linear trajectory with a much smaller slope at the resonance
mass. Moreover, we show that if a linear trajectory with a slope of typical
size is imposed for the f_0(500), the corresponding amplitude is at odds with
the data. This provides a strong indication of the non-ordinary nature of the
sigma meson.
