In previous studies of troponin using molecular dynamics methods, conclusions were difficult to sustain due to questions about the box size used and the length of simulations . Our extended simulations using a 140 Å cubic water box has avoided these problems and now allow us to demonstrate that Ca 2+ -saturated troponin exhibits a considerable range of motion and that NcTnI, the "inhibitory peptide" and the CcTnT can fluctuate over a range of conformations. The N-terminal peptide of troponin I is located on the surface of the N terminal domain of troponin C.