The study of protein internal motions from analysis of C-13 and N-15 NMR relaxation data and auto- and crosscorrelation spectral densities is being pursued in many labs. Model-free approaches and derived motional order parameters are normally used to interpret NMR relaxation data and internal mobility in proteins and peptides. Correlated motions can substantially modify the behavior of NMR auto- and cross-correlation spectral density functions and the values of derived motional order parameters. Here, a simple model is proposed to describe small amplitude (less than about 60 degrees or 1 rad), internally restricted correlated rotations (IRCR) in peptides and proteins in order to analyze order parameters. Bond rotations are represented by vectors whose motions are correlated by a correlation coefficient, c(ij), which is the cosine of the angle between these vectors. Order parameters for NH, CalphaH and CbetaH bond motions have been calculated from molecular dynamics simulations performed on short peptides with well-defined alpha-helix and beta-sheet structures in order to derive values for c(ij). General equations relating dipolar auto- and cross-correlation order parameters for CalphaH, CbetaH, and NH bonds to c(ij) have been derived. The sign of c(ij) depends on the specific motional correlation within a particular molecular conformation. For glycine phi, psi rotations, the sign of c(ij) can be derived from analysis of dipolar auto- and cross-correlation order parameters. Long-range motional correlations are observed with hydrogen bonds modulating internal mobility. In general, backbone NH order parameters, S-NH(2), are more sensitive to structure than are CalphaH order parameters, S-CH(2). S-CH(2) is increased and (SNH)-N-2 is decreased when correlation coefficients c(psi phi) and c(phi psi) are decreased and increased, respectively.