The effect of uniaxial pressure on phase composition, aminoacid side-chain and backbone dynamics, as well as rigid domain sizes of hard alpha-keratin from human fingernail clippings was investigated by H-1 solid-state and C-13 cross-polarization MAS NMR spectroscopy. Proton spin-diffusion NMR experiments revealed that the rigid-domain sizes increased upon compression. The C-13 carbonyl resonance components were shown to be very sensitive to the transition of alpha-helices to beta-sheets induced by uniaxial compression. Carbon-13 longitudinal relaxation in the rotating frame showed dynamic heterogeneity of aminoacid residues especially during the alpha-helix to beta-sheet transition. (C) 2011 Published by Elsevier B.V.