X-ray and mechanical experiments were performed using permeabilized porcine left ventricle wall muscle. The frozen muscle was thawed in skinning solution at room temperature before dissection into smaller strips and skinned at room temperature for 3 hours. Permeabilized fiber bundles were further dissected into preparations with a length of 4 mm with a diameter of 200 µm prior to attachment of aluminum T-clips to both ends for X-ray experiments. X-ray diffraction patterns were collected at BioCAT beamline on a MarCCD 165 detector (Rayonix Inc., Evanston IL) with a 1 s exposure time as a function of five increasing dATP compositions (0%, 2%, 10%, 25%, and 100%) with the total NTP concentration (dATP + ATP) remaining constant at 2.5 mM after 10 min incubation in each solution.