Final answer:
Myosin and actin molecules directly participate in cross bridge formation during muscle contraction, with energy from ATP facilitating the cycle of attachment, power stroke, and detachment.
Step-by-step explanation:
The two molecules that participate directly in cross bridge formation in muscle contraction are myosin and actin. Cross bridge formation is initiated when the myosin head with bound adenosine diphosphate (ADP) and inorganic phosphate (Pi) attaches to the actin filament. During the power stroke, the myosin head bends, releasing ADP and Pi, and pulls the actin filament toward the center of the sarcomere. The cycle is completed with the binding of another ATP molecule to the myosin head, causing the cross-bridge to detach and preparing the myosin for the next cycle.