Non-linear function model of voice pitch dependency on physical and mental load.

The present work describes that under increasing physical load the voice fundamental frequency (voice pitch) remains on a given level as long as the physical load is well tolerated by the subject, whereas heart rate and blood pressure continuously increase during increasing physical load. This voice pitch level was compared to voice pitch levels under mental load. Using a word recognition system, 11 well trained, young male subjects had to solve 2 moderate mental load tasks. Before, during and after each task, there were structured relaxation phases. The physical load protocol was a standard bicycle stress test. In each protocol phase the subjects had to count from 1 to 10 in order to provide a standardized speech sample. Heart rate and blood pressure were recorded in all phases. Voice frequency was at average 106 +/- 5.2 Hz in the relaxation phases ('rest level') and was increased under mental load (115.9 +/- 5.7 Hz, Pillais-P = 0.037). During physical stress testing, voice pitch remained unchanged ('tolerated load level') between 100 and 200 W (117.4 +/- 4.8 Hz) and increased shortly before physical exhaustion ('exhaustion level', 275-350 W, 142.9 +/- 5.6 Hz, Pillais-P = 0.007). In contrast, heart rate and blood pressure increased continuously with the physical load. Three voice pitch levels could be verified also individually for each subject. For the practical monitoring of emotional stress the individual anchor frequencies for these levels must be assessed. These data indicate that the relationship between both types of load and voice pitch is non-linear with multiple plateaus and transition functions between them.