Final answer:
When a frog's gastrocnemius muscle is stimulated with the highest frequency possible, the student will observe complete tetanus, characterized by continuous contraction without relaxation phases.
Step-by-step explanation:
If a student stimulates the gastrocnemius muscle of a frog with the highest frequency possible, they will observe complete tetanus. This occurs when the frequency of motor neuron signaling is so high that the relaxation phase between contractions disappears, resulting in continuous contraction. Each muscle twitch in the state of complete tetanus is added to the previous one without any relaxation, causing a sustained and maximum contraction. This differs from a single twitch, which is an isolated contraction, and from incomplete tetanus, where there is still a short relaxation phase between contractions.
In contrast, treppe, or the 'staircase effect', is seen when a dormant muscle begins contracting and shows a gradual increase in tension with subsequent contractions, similar to ascending a staircase. This phenomenon is not related to the highest frequency stimulation but rather to a series of stimulations given to a resting muscle.