The mechanism of the Ca 2+ switch has been elucidated by the combined efforts of biochemists and structural biologist over the last 30 years, culminating in high resolution cryo-EM images of whole thin filaments at 4.8 Å resolution combined with the fitting of structures from X-ray diffraction at 2.6 Å resolution . However, these structural methods can only partially describe muscle regulation. Ca 2+ binding and switching on the thin filament is a multistep dynamic process, but current methods only show static structures at the extreme "no Ca 2+ " and "high Ca 2+ " states. Key parts of troponin, including the 'inhibitory' peptide (138-147) of cTnI and the Cterminal 18 amino acids of cTnT are not resolved experimentally, implying that they are disordered.