Dr. Johnson began Part 2 of his presentation regarding how the idea of exercise is to have some sort of repeated muscle use or stress designed to induce specific adaptations. The goals are to increase the strength or endurance of the muscles. Vocal exercises are built on both sides of the continuum. Endurance training involves a long duration of this activity under low load with high repetitions so we can have a power output over longer periods of time. With resistance training, we are thinking of short durations of activity with high load and typically not many repetitions. Resistance training with the voice is trickier to apply. He referred to his work at the University of Wisconsin prior to arriving at NYU. He discussed the advantages of using a rat model based on ultrasonic vocalizations. Rats produce these by using the same underlying laryngeal neuromuscular mechanisms that we use to produce our vocalizations as humans. He showed a video of how rats are trained and discussed some findings of research that was undertaken, showing how louder vocalizations were achieved. Another study included younger rats and changes in muscle fiber type composition.
In Part 1 of his presentation, Dr. Johnson reviewed typical changes in the voice that relate to aging. His research group does MRI work and imaging studies in both humans and rodents. An increase in the number of older adults has helped to shift research into how to improve the quality of life among this group. He likes the following definition of aging: "It is a time-independent series of cumulative, progressive, intrinsic, and deleterious functional and structural changes that usually begin to manifest themselves in reproductive maturity and eventually culminate in death." A hallmark of aging is individual variability. Changes due to aging are intrinsic and should be considered independently from external factors such as disease. The sound of our voice changes in pitch and vocal quality as we grow older. He compared the voice of actress Katherine Hepburn on two occasions separated by 50 years, involving factors, such as speech rate and articulation. He discussed the underlying physiology of voice production. With age, the primary effect on the vocal tract is muscle atrophy, which in relation to aging is called sarcopenia. He discussed the respiratory system. The primary change that influences voice is calcification of the costal cartilages and weakening of respiratory muscles, which leads to decreased respiratory capacity. A big cause of an increased effort to get the voice to work is what happens at the level of the larynx.