High-resolution relaxometry was also used to determine motions of protein sidechains. HR relaxometry was used to measure site-specific carbon-13 relaxation rates in protein methyl groups in the model protein ubiquitin. Specific isotopic labeling of methyl groups in isoleucine side chains was employed to obtain isolated C 1 H 2 H2 groups, for which carbon-13 relaxation is slow enough to minimize polarization losses during the transfer between high and low fields. Relaxation rates were measured over two orders of magnitude in magnetic field strength, down to 0.33 T. Heteronuclear nuclear Overhauser effects (NOEs) allowed to capture high-frequency motions, while parameters of slower motions were constrained by low-field longitudinal relaxation rates. It was possible to decompose motions of methyl group dynamics into three independent components: fast methyl group rotation, orientational motion of the CC bond, and global rotational diffusion of the protein. Fast methyl-group rotation was modeled using an order parameter set by the geometry of the methyl group and a single correlation time τ 𝑚𝑒𝑡 , while the orientational motion of the CC bond was described with an extended modelfree approach with two order parameters (𝑆 𝑓 2 and 𝑆 𝑠 2 ) and their associated correlation times (τ 𝑓 and τ 𝑠 ) for fast and slow motions, respectively.