The nature of the extreme kinematics in the extended gas of distant radio galaxies ( z > 0.7 ) is still an open question .
With the advent of the 8-10 m telescope generation and the development of NIR arrays we are in the position for the first time to develop a more detailed study by using lines other than Ly \alpha and [ OII ] \lambda 3727 depending on redshift .
In this paper we review the main sources of uncertainty in the interpretation of the emission line kinematics : the presence of several kinematic components , Ly \alpha absorption by neutral gas/dust and the contribution of scattered light to some of the lines .
As an example , several kinematic components can produce apparent , false rotation curves .
We propose methods to solve these uncertainties .

We propose to extend the methods applied to low redshift radio galaxies to investigate the nature of the kinematics in distant radio galaxies : by means of the spectral decomposition of the strong optical emission lines ( redshifted into the NIR ) we can isolate the different kinematic components and study the emission line ratios for the individual components .
If shocks are responsible for the extreme kinematics , we should be able to isolate a kinematic component ( the shocked gas ) with large FWHM ( \geq 900 km s ^ { -1 } ) , low ionization level [ OIII ] \lambda 5007/H \beta \sim 2-4 and weak HeII \lambda 4686/H \beta \leq 0.07 , together with a narrow component ( \leq few hundred km s ^ { -1 } ) with higher ionization level and strong HeII emission ( HeII/H \beta \sim 0.5 )