A Tutorial on Skeletal Muscle Metabolism and the Role of Blood Lactate: Implications for Speech Production

PURPOSE

The purpose of this tutorial is threefold: (a) present relevant exercise science literature on skeletal muscle metabolism and synthesize the limited available research on metabolism of the adult human speech musculature in an effort to elucidate the role of metabolism in speech production; (b) introduce a well-studied metabolic serum biomarker in exercise science, lactate, and the potential usefulness of investigating this metabolite, through a well-established exercise science methodology, to better understand metabolism of the musculature involved in voice production; and (c) discuss exercise physiology considerations for future voice science research that seeks to investigate blood lactate and metabolism in voice physiology in an ecologically valid manner.

METHOD

This tutorial begins with relevant exercise science literature on the basic cellular processes of muscle contraction that require energy and the metabolic mechanisms that regenerate the energy required for task execution. The tutorial next synthesizes the available research investigating metabolism of the adult human speech musculature. This is followed by the authors proposing a hypothesis of speech metabolism based on the voice science literature and the application of well-studied exercise science principles of muscle physiology. The tutorial concludes with a discussion and the potential usefulness of lactate in investigations to better understand the metabolism of the musculature involved in vocal demand tasks.

CONCLUSION

The role of metabolism during speech (respiratory, laryngeal, and articulatory) is an understudied yet critical aspect of speech physiology that warrants further study to better understand the metabolic systems that are used to meet vocal demands.

An eclectic Voice Therapy Program for the Treatment of Hyperfunctional Voice Disorders (HFVD)

PURPOSE

An eclectic voice therapy program includes sequenced and structured set of exercises combining direct and indirect intervention methods. Tailor-made exercise prescription with specific cultural adaptations are needed to provide a holistic change to voice quality.1 This study detailed the construction of an exercise prescription for participants with hyperfunctional voice disorder [HFVD] in the Indian context.

METHOD

The exercise program was developed based on literature related to vocal therapy approaches and delivery methods. Adaptations were introduced to a selected set of exercises. Five voice experts verified the exercises and their prescription for content and feasibility of use in the Indian context. Modification suggested by the experts were included for framing the final version of the exercise program. This structured therapy program was planned for 6 weeks (30 minutes duration/session offered individually twice per week, with a gap of two days between sessions in a week) with the goals to improve voice quality, flexibility, and endurance while speaking. Five participants with HFVD partook in the study for pilot testing. Stroboscopy, perceptual voice analysis, Dysphonia Severity Index (DSI) and Vocal Fatigue Index in Tamil (VFI-T) were used to report the therapy outcomes. Participants' report on the learning process and generalization of the program were documented. Wilcoxon-signed rank test was used to test the pre-post outcome measures.

RESULTS

An eclectic voice therapy program, i.e., Comprehensive Voice Habilitation Program [CVHP] was constructed and it included vocal hygiene instructions, warm-up & cool-down, easy onset, resonant voice, and carry over exercises. Participants completed the program in 14-18 sessions (over 7 to 9 weeks of therapy). All participants showed significant changes in vocal fold movement patterns, reduction in ventricular hyperadduction, overall grade of voice quality, DSI and VFI-T. Participants reported that pictorial illustrations, feedback, and monitoring sheets were useful in learning the exercises.

CONCLUSION

CVHP showed significant change in the voice-related outcome measures and was a viable program for treating HFVD.

Potential Biophysiological Mechanisms Underlying Vocal Demands and Vocal Fatigue

Patients with complaint of vocal fatigue have perceptual, acoustic, and aerodynamic outcomes that are heterogeneous in nature. One reason may be due to different underlying biophysiological mechanisms that lead to these heterogeneous clinical presentations. Five potential mechanisms are proposed: neuromuscular, metabolic, vocal tissue, afferent, and central neural. Analytical frameworks and study designs to study these mechanisms are also addressed. A better understanding of biophysiological mechanisms of vocal fatigue can improve precision of therapeutic approaches. It can also help shift management from symptom-based to etiology-focused approaches for vocal fatigue.

The Measurement and Effects of Vocal Load in Singing Performance. How Much Singing Can a Singer Sing if a Singer Can Sing Songs?

Singing as both an art form and physical activity demands a level of health and skill fitness to meet performance demands. The determination of performance fitness relies on performers' self-evaluations of their vocal capacity for performance, based, amongst other factors, on the current vocal status and ability to manage the associated vocal load. Measurement of load and the impact on the vocal mechanism is complex and influenced by many intrinsic and extrinsic factors. Researchers have attempted to quantify vocal load effects by measuring physical impact stress on the vocal folds, self-reported perceived exertion, and/or clinical evaluation of physiologic, acoustic, or perceptual changes. Most studies have been conducted in laboratory rather than in performance contexts and studies on singers are substantially lacking. Heavy vocal load has been causally associated with the development of voice disorders, although the exact relationship and thresholds for acquiring laryngeal pathology require further elucidation, and little is also known about the development of voice disorders among singers. Further understanding of the short-term and cumulative effect on the vocal folds of performing as a singer and the nature and prevalence of voice problems among singers is crucial to the determination of appropriate prevention and therapeutic management.