The local changes in troponin described above lead to macroscopic changes that can be compared with experiment. We have based our analysis on the consensus model of Ca 2+ switching as summarised by Stevens et al. Ca 2+ activation of troponin is a two-step process: first Ca 2+ binds to site II of troponin C, then the hydrophobic patch of cTnC opens (energetically unfavoured transition state) and the switch peptide binds to the open patch forming the active state . Since our studies are all in the presence of Ca 2+ bound we only see the active state.