Expiratory Muscle Training Increases Pressure Support in High School Band Students

Abstract

An experiment to increase expiratory muscle strength for instrumentalists, using a high-intensity, low-repetition expiratory training method, was conducted with 40 healthy high school band players. Subjects trained five days per week for 2 weeks using four sets of six training breaths for a total of 24 training breaths with a spring-loaded pressure relief valve that provided an adjustable threshold. The training valve pressure was set at 75% of the subject's measured maximum expiratory pressure (up to 80 cm H₂O). Results demonstrated that high-intensity, low-repetition expiratory exercises significantly increased expiratory pressure generating capacity in these subjects and the degree of the training effect was similar regardless of the instrument the band member played. The training effect occurred within 2 weeks of initiating expiratory muscle training. Thus, this simple method of expiratory-specific strength training is effective and efficient for increasing expiratory pressure support in high school band students and has possibilities of a respiratory support device for many high pressure generating purposes. The potential mechanisms of the training effect are discussed.

Introduction

The ability to produce sound from a musical instrument that requires the musician to blow air into the instrument is, in part, a function of the pressure the musician can generate. Contraction of the expiratory muscles, the elastic recoil of the respiratory structures, and the contraction of the oral-pharyngeal muscles are the sources used to produce this pressure. The first two pressure sources are responsible for the generation of subglottal pressure, which is referred to as pressure support. Pressure support is the foundation of all other pressure changes. This subglottal pressure provides the driving force for air to move out of the lung, into the upper airways, out of the mouth, and into the instrument. The action of the larynx, pharynx, oral cavity, mouth, and lips shape the subglottal pressure. The frequency of sound (range) is also a function of the driving pressure, that is, the greater the pressure, the higher the note that can be produced. The driving pressure is also essential for the control and duration of a sustained note.

The importance of pressure support has long been recognized and many techniques have been developed to increase support and to control the support pressure. The magnitude of the support is a direct function of the musician's ability to generate pressure with active contraction of the expiratory muscles. The diaphragm is the primary inspiratory muscle and must relax for the expiratory muscles (particularly the abdominal muscles) to produce lung compression and thereby generate the positive subglottal pressure. Therefore, controlled relaxation of the diaphragm appears to be very important in support control. However, the contraction of the diaphragm counteracts the actions of the expiratory muscles in the generation of the magnitude of support. Thus, inspiratory training techniques that are designed to increase diaphragmatic strength do not increase the subglottal pressure needed for expiratory tasks, although we commonly come across individuals who believe they are contracting their diaphragm to produce positive expiratory pressures.

Training methods for increasing expiratory muscle strength to assist in developing higher-pressure support have been used with mixed success. Abdominal exercises, such as sit-ups, increase abdominal muscle strength for moving the body trunk, and help maintain a tight abdomen, but do not increase one's ability to generate greater maximum expiratory pressures (MEP) primarily because the muscle training techniques are task specific. This means that in order for a person to increase expiratory pressure generating strength, an exercise that requires them to actively contract the expiratory muscles to blow harder is mandatory.

Several devices have been developed to increase the resistance to expiratory airflow, making it harder to blow air out the mouth. This type of exercise meets the activity specific requirement for muscle training, but provides only modest increases in MEP. The magnitude of the resistance used for training varies but is, generally, a high-repetition, low-intensity exercise that requires the person to generate pressures less than 50% of MEP. The magnitude of the pressure is a function of the airflow rate, which decreases as the expiration progresses. This reduces the expiratory muscle effort with decreasing airflow rate and reduces the expiratory muscle training effect. Forcing the person to maintain a constant airflow rate for the entire expiratory effort in part compensates for this declining expiratory effort effect. With most resistive respiratory muscle training methods, MEP increases ranged from 20% to 30% with training.¹

Our laboratories developed a high-intensity, low-repetition inspiratory training method that replaces the resistance devices with a pressure relief valve. The pressure relief valve has an adjustable spring that holds a cover over the breathing tube. It keeps it closed until sufficient pressure is produced to overcome the spring strength. The cover is then pushed open and air flows. The method requires the person who is using the device to generate a minimum pressure throughout the entire breath for lung volume to change. This specifically exercises the respiratory muscles in a breathing specific manner. The ability of the respiratory muscles to generate force changes with changing muscle length (related to lung volume change). The pressure relief valve used for inspiratory muscle training increases the respiratory muscle demand as lung volume increases, the diaphragm gets shorter, and the ability of the diaphragm to generate force decreases. This provides a greater muscle training effect over the entire inspiratory effort when compared to resistive methods. The mechanism that is most likely responsible for this change is neural, particularly when the training period is short in duration. The strength of a muscle relies not only on the structural integrity of the muscle but also on the ability of the nervous system to properly activate the muscle. Previous literature on strength training of the limbs suggests that training results in adaptive changes to the nervous system, allowing more specific muscle movements and better coordination of control, resulting in greater force generation.2, 3

Our previous results, with other subject groups, appear to support the limb literature. We have reported an average 50% increase in maximum inspiratory pressure (MIP) in normal young adult subjects.⁴ The inspiratory muscles were trained with the valve pressure set at 75% of maximum inspiratory pressure. This increase in maximum inspiratory pressure is greater than previous reports using resistive methods. A similar increase in MIP was obtained in a patient with laryngeal papilloma and documented as having a high laryngeal resistance.⁵ We hypothesized that inverting the pressure relief valve to have subjects expire through it would provide an expiratory muscle exercise specific to breathing out and increase muscle strength as measured by the MEP. This hypothesis was tested in high school band students.