Final answer:
Changing the discharge frequency of a motor unit can change the tetanic force output from that unit. Increasing the frequency of motor neuron signaling can lead to a higher muscle tension, resulting in incomplete or complete tetanus.
Step-by-step explanation:
If the frequency of motor neuron signaling increases, summation and subsequent muscle tension in the motor unit continues to rise until it reaches a peak point. The tension at this point is about three to four times greater than the tension of a single twitch, a state referred to as incomplete tetanus.
During incomplete tetanus, the muscle goes through quick cycles of contraction with a short relaxation phase for each. If the stimulus frequency is so high that the relaxation phase disappears completely, contractions become continuous in a process called complete tetanus.