Final answer:
The cross-bridge cycle is integral to muscle contraction, and too much ADP indicates low ATP levels, which hinders the detachment of the myosin head from actin and prevents another cycle from starting, leading to impaired muscle contraction.
Step-by-step explanation:
Too much adenosine diphosphate (ADP) can prevent the cross-bridge movement in muscle contraction. When the myosin head is in the high-energy 'cocked' position, it is attached to actin with ADP and inorganic phosphate (Pi) bound to it. The release of Pi following the power stroke leads to a stronger attachment between myosin and actin, and the subsequent releasing of ADP is necessary for the cross-bridge to detach; this is essential to allow the movement of actin towards the M-line.
As long as ATP is present, it will bind to the myosin, leading to the detachment of the myosin head from actin and allowing for a new cross-bridge cycle to occur, resulting in muscle contraction. If there is an excess of ADP, it indicates a lack of sufficient ATP, which in turn prevents the necessary release and rebinding of the myosin head to actin during the cross-bridge cycle. Consequently, muscle contraction cannot continue efficiently because the cycles of attachment and detachment are halted.