  The octet-baryon axial-vector charges and the g1/f1 ratios measured in the
semileptonic hyperon decays are studied up to O(p^3) using the covariant baryon
chiral perturbation theory with explicit decuplet contributions. We clarify the
role of different low-energy constants and find a good convergence for the
chiral expansion of the axial-vector charges of the baryon octet, g1(0), with
O(p^3) corrections typically around 20% of the leading ones. This is a
consequence of strong cancellations between different next-to-leading order
terms. We show that considering only non-analytic terms is not enough and that
analytic terms appearing at the same chiral order play an important role in
this description. The same effects still hold for the chiral extrapolation of
the axial-vector charges and result in a rather mild quark-mass dependence. As
a result, we report a determination of the leading order chiral couplings,
D=0.623(61)(17) and F=0.441(47)(2), as obtained from a completely consistent
chiral analysis up to O(p^3). Furthermore, we note that the appearance of an
unknown low-energy constant precludes the extraction of the proton octet-charge
from semileptonic decay data alone, which is relevant for an analysis of the
composition of the proton spin.
