Vocal Effects in Military Students Submitted to an Intense Recruit Training: A Pilot Study

Abstract

Objectives: This study aims at evaluating the vocal parameters of military officers before and after an Intense Recruit Training (IRT), consisting of a 48-hour exercise protocol involving high vocal demand combined with physical effort, lower body hydration levels, and fewer hours of sleep.

Study design: Eighty-three young male military officers (aged between 18 and 22 years) were recorded on three occasions: before, immediately after, and 2 weeks after the IRT.

Methods: Maximum phonation times (MPTs) using vocalization of the vowel /a/, the fricative consonants /s/ and /z/, and connected speech samples were collected. A number of acoustic parameters were analyzed: mean fundamental frequency, mean intensity, jitter, shimmer, harmonics-to-noise ratio, spectral emphasis (acoustic correlate of vocal effort), H1-H2 (difference between the amplitude of the first and the second harmonic), and the frequency and intensity ranges. For the immediate effects, statistical analyses were conducted using a paired sample t test (P = 0.05) to compare two moments: before and after the IRT. For the long-lasting effect, statistical analyses were conducted using a one-way analysis of variance (ANOVA) test (P = 0.05) to compare between all three moments (before, immediately after, and 2 weeks after the IRT).

Results: The MPTs of /a/, /s/, and /z/, the acoustic parameters as spectral emphasis, and the mean of intensity showed statistically significant changes between the data from before and immediately after training took place. The MPT of /a/ and the intensity range showed statistically significant changes between the measurements taken immediately after training and the ones taken 2 weeks after training; there were significant differences in the comparisons between the three groups of data acquired.

Conclusions: Some of the acoustic parameters were able to identify changes in the vocal conditions of the military students as consequence of high intensity voice and physical military training. The changes in the vocal intensity and MPT parameters seem to be related to general fatigue and lower hydration. The absence of impact in some parameters, specially 2 weeks after the IRT, may reveal that the students' voice is getting used to the military activities.

Keywords: Acoustic analysis; Military; Occupational health; Voice disorders.