  Galaxy clusters are the endpoints of structure formation and are continuously
growing through the merging and accretion of smaller structures. Numerical
simulations predict that a fraction of their energy content is not yet
thermalized, mainly in the form of kinetic motions (turbulence, bulk motions).
Measuring the level of non-thermal pressure support is necessary to understand
the processes leading to the virialization of the gas within the potential well
of the main halo and to calibrate the biases in hydrostatic mass estimates. We
present high-quality measurements of hydrostatic masses and intracluster gas
fraction out to the virial radius for a sample of 12 nearby clusters with
available XMM-Newton and Planck data. We compare our hydrostatic gas fractions
with the expected universal gas fraction to constrain the level of non-thermal
pressure support. We find that hydrostatic masses require little correction and
infer a median non-thermal pressure fraction of $\sim6\%$ and $\sim10\%$ at
$R_{500}$ and $R_{200}$, respectively. Our values are lower than the
expectations of hydrodynamical simulations, possibly implying a faster
thermalization of the gas. If instead we use the mass calibration adopted by
the Planck team, we find that the gas fraction of massive local systems implies
a mass bias $1-b=0.85\pm0.05$ for SZ-derived masses, with some evidence for a
mass-dependent bias. Conversely, the high bias required to match Planck CMB and
cluster count cosmology is excluded by the data at high significance, unless
the most massive halos are missing a substantial fraction of their baryons.
