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.
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