Myofibril activation and relaxation kinetics were assessed. For E-H, band and normal for each sex are combined. Using myofibrils isolated from the LV, (A) Rate of activation, (B) rate constant of tension redevelopment, (C) rate of linear relaxation, and (D) rate of exponential relaxation were assessed. Statistical analysis to determine significance was performed using (A-D) welch’s t-test.