Below 5 kHz, it is difficult (but possible with advanced techniques) to apply field-cycling relaxometry, which provides the evolution of the longitudinal relaxation rate (R₁) as a function of the Larmor frequency. Moreover, residual dipolar or quadrupolar couplings, if not negligible, would make the interpretation of such measurements dubious. Rotating frame relaxation measurements constitute a possible remedy since, by varying the amplitude of the spin-lock radiofrequency field, it is possible to explore the frequency dependence of the relevant relaxation rate (R_1ρ) down to very low frequencies. However, there is a problem in connecting the R₁ and R_1ρ dispersion curves because of the differences, in terms of spectral densities, of the theoretical expressions of these two relaxation rates. A method based on the random fields relaxation mechanism, has been developed and shown, through several examples, to be fairly efficient. Along with R₁ measurements performed at high frequency with conventional NMR spectrometers, it proved possible to unravel, through a complete dispersion curve, all molecular motions occurring in complex systems.