  The light axial vector mesons can couple to $K^*\bar{K}+c.c.$ in an $S$ wave
at the tree level. Due to the near-threshold $S$-wave interactions the
couplings can be affected by the final state interactions. It is of peculiar
interest that the pion exchange between $K^*\bar{K}+c.c.$ can go through a
triangle diagram which is within the kinematics of the triangle singularity
(TS). This mechanism will introduce energy dependence and a $D$-wave amplitude
to the vertex couplings. Hence, it should be necessary to investigate the role
played by the $K^*\bar{K}+c.c.$ threshold in order to have a better
understanding of the light axial vector spectrum.
