  This paper presents a principal components analysis of rotation curves from a
sample of low surface brightness galaxies. The physical meaning of the
principal components is investigated, and related to the intrinsic properties
of the galaxies. The rotation curves are re-scaled using the optical disk
scale, the resulting principal component decomposition demonstrates that the
whole sample is properly approximated using two components. The ratio of the
second to the first component is related to the halo steepness in the central
region, is correlated to the gas fraction in the galaxy, and is un-correlated
to other parameters. As a consequence the gas fraction appear as a fundamental
variable with respect to the galaxies rotation curves, and its correlation with
the halo steepness is especially important. Since the gas fraction is related
to the degree of galaxy evolution, it is very likely that the steepness of the
halo at the center is a consequence of galaxy evolution. More evolved galaxies
have shallower central profile and statistically less gas, most likely as a
consequence of more star formation and supernovae. The differences in
evolution, gas fractions and halo central steepness of the galaxies could be
due to the influence of different environments.
