Final answer:
An increased threshold for initiating an action potential is linked to the relative refractory period, as it requires a stronger stimulus to start a new action potential due to ongoing potassium outflow.
Step-by-step explanation:
An increased threshold is associated with the relative refractory period. During the absolute refractory period, another action potential cannot start because the voltage-gated Na+ channel is inactivated. Once the channel is ready again, and if the membrane potential is still below the threshold (less than -55 mV), then a new action potential could be initiated by a stronger-than-normal stimulus. This higher threshold of stimulus needed is due to the flow of K+ out of the cell, which makes it harder for incoming Na+ to depolarize the cell, instead, it helps to prevent the cell from hyperpolarizing too much during the relative refractory period.