Normal modes in internal coordinates (IC) furnish an excellent way to model functional collective motions. Here we present an enhanced version of our versatile NMA-IC framework, iMod (1). Even though the complexity reduction obtained from the IC and the employ of coarse-grained (CG) representations, the diagonalization step remained as a bottleneck for large macromolecular machines. Now, virus, long F-actin filaments or large microtubules can be studied with moderate CG representations by solving the large-scale eigenvalue problem on shared-memory multiprocessors using ad doc algebra procedures. Also, new parameterization of the elastic model has been done to improve the overall conformational flexibility description. By extending its applicability to larger systems and by improving elastic network potentials, we expedite the study of the collective conformational changes of such biological relevant complexes and their functional implications. 1. López-Blanco JR, Garzón JI, Chacón P. (2011) iMod: multipurpose normal mode analysis in internal coordinates. Bioinformatics. 27 (20): 2843-2850.