Laying the Groundwork to Study the Heterogeneous Nature of Vocal Fatigue

Vocal fatigue has remained an elusive construct-despite its significant impact on communication, vocation, and quality of life. Current frameworks define vocal fatigue in the context of vocal demands and vocal demand-responses. However, the impact of factors like individuals' baseline vocal fitness and perception of the demand are not well understood. What is also not well understood are the effects of specific vocal demand ingredients on an individual's vocal demand responses. Furthermore, current outcome measures utilized to capture vocal fatigue lack sensitivity and underlying mechanisms are poorly understood. These gaps have led to inconclusive next steps in how to best define, assess, monitor, and manage vocal fatigue. A conceptual framework is needed to study and better understand vocal fatigue constructs. Such a framework should consider the individual's baseline physiology, psychology, key vocal demand ingredients, and biophysiological mechanisms underlying demand responses. The objective of this paper is to help the reader better understand the complex and heterogeneous nature of vocal fatigue and its impact on reliable assessment and monitoring. Future studies will require better elucidation of vocal demand ingredients, will need more sensitive vocal demand response measures, and will need to take in to account an individual's baseline physiology and psychological factors.