Expiratory Muscle Strength Training (EMST)
Respiratory muscle strength training (RMST) is a strength-based approach for increasing the force generating capabilities of the respiratory muscles. RMST involves two types of exercise: expiratory muscle strength training (EMST) and/or inspiratory muscle strength training (IMST).
EMST is perhaps the more widely researched form of RMST within the field of dysphagia - though IMST is becoming increasingly popular with growing evidence to support its use. EMST has been found to consistently elicit improvements in cough function in people with dystussia, with less consistent (albeit still promising) findings related to its effect on swallowing rehabilitation.
My thoughts: I hypothesize that a strength-based approach to cough rehabilitation (e.g., EMST) is likely the most ideal approach to cough rehabilitation if the primary cause of dystussia is due to peripheral muscle weakness. However, if the primary cause of dystussia is due to changes in motor control and coordination, then a skill-based approach to cough rehabilitation (e.g., voluntary cough skill training) may likely be a more effective approach to cough rehabilitation.
This tutorial describes how to go about prescribing EMST, once (and if) you determined EMST is appropriate for your patient.
First, obtain a pressure-threshold EMST device. Pressure-threshold devices (e.g., EMST-150, EMST75 Lite, Respironics Threshold PEP) include calibrated, one-way, pressure valves that require patients to generate a predetermined amount of pressure to open the valve. This allows for the patient and clinician to determine when a repetition was successfully completed. Most research has been conduced with the EMST-150 device, but any pressure-threshold device will work.
Note: Continuous-stream (non-pressure-threshold) devices (e.g., The Breather) are typically less expensive, but should be avoided for clinical use. These devices use different size openings through which the patient blows in order to facilitate different resistance levels. Blowing through a narrower opening is harder to blow through than blowing through a wider opening. However, this is only true if the speed of exhalation is remaining constant. For example, it is easier to blow slowly through a narrow straw than if you tried to blow as quickly as possible. Because it is impossible to control for expiration rate, it is impossible to determine the amount of force being generated by the patient, and therefore, impossible to guide therapy in any systematic way and determine if a patient successfully completed a repetition.
Second, determine the intensity level at which the patient should be trained (e.g., very light, light, moderate, hard). Moderate-to-hard intensity is what is generally recommended for novice and intermediate exercises to improve strength, which is likely the most suitable option for rehabilitation (rather than training athletes). Moderate-to-hard intensity is what I typically recommend for patients, unless I am working with people whereby moderate-to-high level intensity is contraindicated.
Third, determine the patient's one repetition maximum (1RM). Do this by having the patient blow through the pressure-threshold device. Find the highest level on the device through which they can blow (blow open the valve). If using the EMST device, look to see where the bottom of the blue knob lines up with the sticker. In the video below, I work my way up resistance levels from 30, to 60, to 90, to 120. I eventually max out at ~150 cmH20. So my 1-RM is 150.
Fourth, set the device to a percentage of the patient's 1RM. The percentage is based off of the recommended intensity level. Moderate intensity involves practicing each repetition at ~70% RM. For example, if a patient's 1RM was 100 cmH20, the they should be training at 70 cmH20 if targeting an intensity of 70% RM. In the below video, I set the device to ~100 cmH20, which is ~70% of my 1RM (150 cmH20). This is done by looking where the bottom of the blue knob is aligning on the colored label. I then complete an EMST set at that 100 cmH20 (70% RM) intensity level.
Fifth, prescribe the practice dose. Using the American College of Sports Medicine guidelines, moderate intensity for middle aged and older adults is 8-12 repetitions per set (at ~70% RM), 2-4 sets per session, 2-3 minutes rest between each set, 1 session per day, 3-4 days per week, for 8-12 weeks. A table from the American College of Sports Medicine characterizing suggestions for light, moderate, and hard intensity is provided below, with the reference at the end of this tutorial.
Note 1: Most EMST research prescribes to a '5x5x5' rule, which involves 5 reps per set, 5 sets per session, 5 days per week. This could be another approach, though admittedly, I use the large body of strength training research to guide the dosing I typically use.
Note 2: For any strength-based exercise, including EMST, consider integrating 0-10 point ratings of perceived exertion to ensure the patient is exerting enough effort (even if set to the appropriate %RM).
Lastly, re-assess the patient's 1RM every week, and adjust the intensity level on the device accordingly in order to maintain the desired intensity level (i.e., ~70% RM). For example, if a patients 1RM at the first treatment session is 80 cmH20, and they were training at 70% RM, then they should be training at ~56 cmH20. If their strength increased the next week such that their new 1RM was 100 cmH20, then to continue training at 70% RM, they should increase the device from ~56 cmH20 to ~70 cmH20. Etc.
Note: The first couple of treatment sessions may involve training the skill to successfully complete EMST. This may include how to hold the cheeks, create a complete labial seal, prevent nasal air escape, set the device, etc.
Garber, C. E., Blissmer, B., Deschenes, M. R., Franklin, B. A., Lamonte, M. J., Lee, I. M., ... & Swain, D. P. (2011). American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Medicine and science in sports and exercise, 43(7), 1334-1359.