# Investigation of Vocal Fatigue Using a Dose-Based Vocal Loading Task
Standard self-administered questionnaires, such as the SAVRa and the Vocal Fatigue Index (VFI), have been used to identify individuals with vocal fatigue, and to characterize their symptoms [23; 24; 25]. [PERSON] and [PERSON] used the SAVRa to quantify vocal fatigue recovery based on 86 participants' tracking reports. The results showed a self-reported 50% recovery within 4-6 h, and 90% recovery within 12-18 h [24]. [PERSON] et al. used one of the three dimensions in SAVRa, i.e., the inability to produce soft voice (IPSV), to track vocal changes in school teachers. The SAVRa scores were then compared with two clinicians' ratings of the participants' \(f0\), and loudness [26]. The overall correlation between self-ratings and clinician ratings was not significant. The average absolute difference score was 1.7. This showed that the clinicians and the teachers had different rating standards. Prolonged or inappropriate voice use is commonly regarded as one of the causes of vocal fatigue. Vocal loading tasks (VLTs) are often used to investigate the relationship between voice use and vocal fatigue in laboratorial settings [1]. Previous VLT studies have typically instructed participants to complete standardized reading tasks of prescribed durations at specific loudness levels [1; 4; 24]. Perceptual, acoustic, and aerodynamic measurements have been used to evaluate changes in voice quality and performance before and after VLTs [4]. Unfortunately, the findings from these studies were often reported as inconsistent. Comparisons across different studies have been at times contradictory. This may have been caused by multiple factors: (1) the prescribed VLT might not have induced a detectable level of vocal fatigue across individuals, (2) the amount of vocal loading across participants may not have been consistent due to the lack of a universal method to quantify vocal loading, and (3) there may have been variability in experimental settings. A more robust vocal loading protocol for VLT is therefore needed to improve consistency, and to allow comparisons across different studies. Amongst methods of quantifying voice use for vocal fatigue assessment, the vocal distance dose, \(D_{d}\), first proposed by [PERSON] et al., was adopted in the present study [27]. The vocal distance dose attempts to approximately quantify the distance traveled by vocal folds during vocal oscillation [27; 28]. It is usually calculated in terms of the fundamental frequency, the sound pressure level, the voicing duration, and the vocal duty ratio. Whether \(D_{d}\) correspondences to the true cumulative vocal fold displacement has not yet been verified. But, as a four-parameter estimates, vocal distance dose is more comprehensive than other metrics that are based on one single parameter. [PERSON] et al. described the procedures to calculate the distance dose using synchronized microphone and EGG data [29]. The EGGsignal was used to locate the peak position for each vocal cycle in the time domain. The microphone signal was used to quantify loudness. [PERSON] et al. used cumulative vocal dose data correlations with subjective measurements in vocal fatigue experiments. An abrupt increase in vocal loading was closely related to a harsher subjective self-reported rating [30]. [PERSON] et al. found that a 10-min intensive VLT with a >80 dB loudness level was comparable to a 45-min teaching task in terms of vocal dose [31]. [PERSON] et al. showed that kindergarden teachers had significantly greater distance doses than elementary school teachers based on an investigation of 12 kinderdarten and 20 elementary school female teachers [5]. [PERSON] and [PERSON] calculated the vocal distance dose and the sound pressure level (SPL) for school teachers during their daily teaching assignments. They found that female teachers had on average a higher (>3.4 dB) loudness level than male teachers, but vocal distance doses did not differ very much between female and males teachers [32].