Two groups, ours (Mainz) and Bochum, have recently been re-evaluating the spin polarizabilities and spin structure functions at low Q, using the baryon chiral perturbation theory (B χPT), the manifestly-covariant counterpart of the heavy-baryon chiral perturbation theory (HB χPT). Whilst the two groups agree that the B χPT framework works better than HB χPT in this sector, their quantitative results disagree in some of the quantities; most notably, the proton spin polarizabilities γ₀ and δLT . These discrepancies are especially intriguing in light of new experimental data coming from the Jefferson Lab “Spin Physics Program”. The preliminary data on the proton are reported by Karl Slifer in a plenary session of this workshop. Another theoretical discrepancy is emerging in the proton-polarizability contribution to the hyperfine splitting (hfs) in hydrogen and muonic hydrogen. Our B χPT calculation shows a significantly smaller effect than the state-of-the-art data-driven evaluations based on empirical spin structure functions. The smaller polarizability contribution leads to a smaller Zemach radius of the proton. This discrepancy could be relevant for the planned first-ever measurement of the ground-state hfs in muonic hydrogen.