You reach a point of steady-state exercise where you're breathing hard and breaking a sweat, but you're able to continue performing the work because you're able to take in enough oxygen to keep up with the exertion.
Some electrophysiological tests are the auditory brainstem response (ABR) test, auditory steady-state response (ASSR) testing, electroencephalic audiometry (EEG) test, and otoacoustic emission testing (OAE).
Auditory steady-state response (ASSR) testing also involves monitoring recorded responses from the scalp of tones at varying frequencies.
Firszt, Jill B., et al. "Auditory Sensitivity in Children Using the Auditory Steady-State Response."
Stempak, D., et al. "Single-dose and steady-state pharmacokinetics of celecoxib in children."