This is the 15322nd most frequent German word.
unterzieht
"Unterzieht" means "subjects (oneself/someone) to [something]."
In this context, "unterzieht" is used reflexively to indicate that the subject (he) subjects himself to a medical examination.
Er unterzieht sich einer medizinischen Untersuchung.
He undergoes a medical examination.
Here, "unterzieht" is used transitively, with "das Experiment" as the subject actively testing the theory.
Das Experiment unterzieht die neu entwickelte Theorie einem Test.
The experiment subjects the newly developed theory to a test.
In this example, "unterzieht" is again used transitively, where "die Firma" is the subject ensuring their products meet quality standards.