Validation of a novel vocal demand task for measuring vocal fatigue: the Fluid Interval Test for Voice (FIT-V)

Abstract

Vocal fatigue is a communication disorder that disproportionately affects occupational voice users such as teachers, call center workers, and religious officials (Cohen et al., 2012; Roy et al., 2004, 2005). Classically, fatigue is composed of two dimensions: perceived fatigability and performance fatigability (Enoka et al., 2021; Enoka & Duchateau, 2016; Hunter et al., 2020; Kluger et al., 2013). Researchers in exercise science use a variety of task protocols to elicit perceived and performance fatigability in working muscle. Only one task protocol, however—loud oral reading—is prevalent in voice research (Fujiki & Sivasankar, 2017). Loud oral reading tasks take 1-2 hours to administer (Fujiki & Sivasankar, 2017) and expose participants to large vocal fold vibratory doses (Cantarella et al., 2014; Smith et al., 2017; Titze & Hunter, 2015) that may place them at risk of phonotraumatic injury. ☐ In the ideal, vocal demand tasks would (1) take fewer than 30 minutes to administer to optimize participant recruitment and retention, (2) minimize vocal fold vibratory dose, and (3) maximize the contractile demands placed on the intrinsic laryngeal skeletal muscles most susceptible to fatigue. The goal of the current study is to validate a novel vocal demand task (the Fluid Interval Test for Voice, or FIT-V) that cleaves as closely as possible to these ideals, with the goal of sparking future vocal fatigue research and detecting, diagnosing, and treating vocal fatigue prior to the point of disability. Three specific aims support this goal: Aim 1 compares vocal fold vibratory dose differences between two variants of the FIT-V task protocol and a control task protocol, assessing whether the FIT-V is equivalent in vibratory dose to current “gold standard” loud oral reading tasks (Titze et al., 2003; Titze & Hunter, 2015). Aim 2 compares changes in perceived exertion across the three tasks. The exploratory Aim 3 screens several potential indices of performance fatigability in the intrinsic laryngeal musculature, including changes in diadochokinetic rate, airflow peak prominence, and breath group adaptations. Together, these aims assess whether a novel, diadochokinetic vocal exercise task founded on principles of physiological specificity and progressive overload may be able to supplement—or even supplant—loud oral reading tasks as the vocal demand task of choice in vocal fatigue research and clinical performance testing. ☐ Broadly, the results of the study suggest that the new FIT-V tasks imposed a substantially smaller vocal fold vibratory dose than loud oral reading tasks while eliciting similar levels of overall perceived exertion. However, the two task types differed considerably with regard to which specific anatomical regions were most affected, and declines in most measures of diadochokinetic performance were not observed. Participants approached the FIT-V tasks in highly individualized ways, hinting at a deeper interplay between motor learning, performance optimization, and fatigue that merits further study.