  In this paper we discuss effective strong coupling constants. Those are well
behaved in the low-Q^2 domain, contrarily to alpha_s from pQCD. We present an
extraction of an effective strong coupling constant from Jefferson Lab
polarized data at intermediate and low Q^2. We also show how these data,
together with spin sum rules, allow us to obtain the effective coupling
constant over the entire Q^2 range. We then discuss the relation between the
experimentally extracted coupling constant and theoretical calculations at low
Q^2. We conclude on the importance of such study for the application of the
AdS/CFT correspondence to QCD.
