So this is our calcium, it binds onto our troponin, it changes its shape, which in turn changes the shape of our tropomycin and that exposes our myosin binding side. So this is step number two. Now, as soon as our binding side is exposed, right before the binding between the thick and the thin filament actually takes place, our myosin head has to basically hydrolyze an ATP molecule. So the myosin heads contain ATP molecules or an ATP molecule. So one ATP per hour myosin head. Now before they can actually bind to the mycin binding side that was just exposed as a result of the binding, the calcium, the ATP must be hydrolyzed into ADP and a phosphate group.