  In this work, we characterize the properties of HB stars in the GCs $\omega$
Cen and NGC 6752. We use dedicated model atmospheres and synthetic spectra
grids computed using a hybrid LTE/NLTE modeling approach to fit the MUSE
spectra of HB stars hotter than 8000 K in both clusters. The spectral fits
provide estimates of the effective temperature, surface gravity, and helium
abundance of the stars. The model grids are further used to fit the HST
magnitudes, meaning the spectral energy distributions (SED), of the stars. From
the SED fits, we derive the average reddening, radius, luminosity, and mass of
the stars in our sample. The atmospheric and stellar properties that we derive
for the stars in our sample are in good agreement with the theoretical
expectations. In particular, the stars cooler than $\sim$15 000 K follow neatly
the theoretical predictions on the radius, log $g$, and luminosity for
helium-normal models. In $\omega$ Cen, we show that the majority of these
cooler HB stars cannot originate from a helium-enriched population with
$Y>$0.35. The properties of the hotter stars (radii and luminosities) are still
in reasonable agreement with theoretical expectations, but the individual
measurements have a large scatter. We use three different diagnostics, namely
the position of the G-jump and changes in metallicity and helium abundances to
place the onset of diffusion in the stellar atmospheres at Teff between 11 and
11.5 kK. Our sample includes two stars known as photometric variables, we
confirm one to be a bona fide extreme HB object but the other is a blue
straggler star. Finally, unlike what has been reported in the literature, we do
not find significant differences between the properties of the stars in both
clusters. We showed that our analysis method combining MUSE spectra and HST
photometry of HB stars in GC is a powerful tool to characterize their stellar
properties.
