EMST (Expiratory Muscle Strength Training) and Speech Therapy - What and why?
Updated: Jun 17, 2021
Not sure what EMST is? We offer it in our service and it is one of my favourite therapies - for many reasons. Let's look first, at the history of EMST so we have a good idea of how it developed... More questions and answers about the protocol itself can be found on our brochure available on Enable's resources pages.
A Brief History of EMST
EMST was developed about 20 years ago at the the University of Florida. It initially began as a collaborative effort between exercise physiologists, neurologists and engineering, but later involved key Professors/Researchers in Speech Pathology, Dr Christine Sapienza, Dr John Rosenbek, and Dr Michelle Troche, (who was originally a PHD student of Dr Sapienza).
The University of Florida has extensively supported and continues to support, research involving EMST as does PN Medical. Additionally, there are ongoing studies as recent as 2019, being completed in other countries such as Australia and a recent review of previous research in 2019, has found ongoing benefits for Speech Therapy clients. The evidence base for EMST grows yearly and the best clinicians keep up with it.
What does EMST target?
EMST was originally developed to improve expiratory respiratory strength, but it was subsequently found to also strengthen some muscles of the upper respiratory tract.
The upper respiratory tract involves all the structures involved in swallowing, and in the pictures above, you can also see the respiratory muscles involved in EMST (picture 3).
EMST allows us to be specific about the muscles we target with exercise. The following muscles are all strengthened by EMST:
The abdominal and internal intercostal muscles in the chest wall (they were the original primary targets of EMST)
Submental (under the chin) muscles important in moving the larynx (they found over time these muscles were helped by EMST)
Muscles that move the vocal folds, and
Muscles of the pharynx, larynx, and soft palate.
Phew!!! That's a lot of work for one exercise.
The x-ray picture below also shows some of the areas that were affected by EMST training, all of which are found in the upper respiratory tract. Observations during EMST include velopharyngeal seal (top arrow), hyoid excursion, arytenoid-to-epiglottic approximation (scaled to distance between C2 and C4 vertebrae), and pharyngeal shortening (bottom arrow). EMST = expiratory muscle strength training (Reference: Hutcheson, K. A., Hammer, M. J., Rosen, S. P., Jones, C. A., & McCulloch, T. M. (2017). Expiratory muscle strength training evaluated with simultaneous high-resolution manometry and electromyography. The Laryngoscope, 127(4), 797–804. https://doi.org/10.1002/lary.26397)
How does EMST work on the muscles?
EMST targets skeletal muscles. All skeletal muscles, over time, are going to degenerate and lose function, whether because of your age or a disease process. However, skeletal muscles have the ability to adapt. This ability to adapt is called neuroplasticity. In order to adapt though, they need to be able to generate force. An example of respiratory force is how strong you cough or are able to cough.
EMST uses a pressure threshold device. It works like weight lifting for your arms. It is not a resistance trainer. For example, blowing through a straw is a resistance exercise. You can change the resistance by blowing slower - but it won't actually build up strength in your respiratory muscles.
EMST relies on the release of pressure via a valve, inside the device. You can increase the pressure, like you would increase the weights you lift in a gym. So you can increase the pressure on your respiratory system muscles, and build up strength. Much like you would build up strength in your arms in a gym.
Skeletal muscles have both fast and slow twitch fibres. Fast twitch fibres generate force but are prone to fatigue (as in coughing). Slow twitch fibres are slow to contract but resistant to fatigue (as in posture). Respiratory Muscle Strength Training, in general, stimulates fast twitch fibres resulting in muscular enlargement or "hypertrophy".
With any exercise, there can also be a detraining effect (i.e. when your muscles go back to their original size after you stop exercising). Skeletal muscles generally return to pre-training levels within 1 month of exercise, however, respiratory muscle gains remain significantly higher than pre-training levels up to 8 weeks after training cessation. Sapienza found that maximal expiratory pressure's (MEP) generally remain above baseline levels following a period of detraining, although studies have shown that they did reduce after 4 and 8 weeks compared to what they were at the end of the initial training period. With Inspiratory Muscle Strength Training (IMST), maximal inspiratory pressures (MIP) were shown to remain above their baseline levels for 6 months or more, on minimal amounts of maintenance (2 days per week).
The benefit for Speech Therapy and our clients
Currently, there are four main benefits to our clients who engage with EMST.
Overall, the research coming out of EMST studies is showing very good changes in muscle forces generating Maximum Expiratory Pressures (MEP). Increased expiratory pressure results in a better ability to produce a higher expiratory flow. A high expiratory flow is critical for coughing.
Coughing is important for preventing food and drink going into the lungs (aspiration), which could lead to a pneumonia (aspiration pneumonia). So if our cough is strong and operating efficiently, we can reduce our risk of aspiration and aspiration pneumonia.
Shortness of Breath
Subjects of various studies have also reported a decrease in the sensation of shortness of breath (dyspnea), which resulted in less anxiety around their shortness of breath and improved quality of life.
Improved swallow safety
EMST has been shown in several studies, to help improve the muscle force generation of the swallow muscles:
Increased submental muscle force generation results in increased hyloaryngeal complex movement, resulting in increased airway protection and upper esophageal sphincter (UES) opening.
The overall result is a "safer swallow".
Speech and EMST
There are fewer studies that have looked at how EMST may improve the speech aspect of our clients i.e. low volume in Parkinson's Disease. However, there are studies beginning to look at this. One hypothesis of how it may help, is that it could work by increasing subglottic pressure (pressure that is generated underneath the vocal folds) and also by increasing the synergy between the diaphragm and the posterior cricoarytenoid (the posterior cricoarytenoid open the vocal folds). This is what happens when we "Think Loud, Think Shout" - it creates a synergic effect between our brain and all the muscles involved in producing voice. It has been shown that "Loud" voicing can stimulate improved articulation and other muscles controlling speech in some neurogenic populations. EMST could potentially help us to generate subglottal (beneath the vocal folds) pressures sufficient enough to produce loud voicing. Work is still ongoing in this area.
A more recent study from 2017 showed improved "speech breathing" patterns for those with Parkinson's Disease, which could naturally help improve the way an individual produces speech.
Who is EMST suitable for?
EMST is suitable for some populations, whilst it's twin, IMST (Inspiratory Muscle Strength Training) is suitable for others. The below table gives a brief overview of which exercise may suit which population.
There are a wide variety of populations who would benefit from either, or or both IMST and EMST, and research is emerging all the time about the diagnostic groups who may benefit.
For example, looking at the above, you can see that Amyotrophic Lateral Scerosis (ALS) or Motor Neurone Disease (MND), as it's commonly known in the UK and Australia, is more suitable for IMST, however, studies are now showing that EMST benefits those clients as well. Additionally, where we traditionally worried about fatigue with those clients, we have now found out that they can exercise their muscles without doing any harm, and that those exercises could potentially protect the muscle functioning, slowing down any muscle deterioration/change. This has lots of benefits in terms of eating/drinking and improving quality of life.
Clients who may not be suitable for EMST include those with occurrence of acute stroke, untreated hypertension, untreated gastroeosophageal reflux, reactive airway disease (like asthma) and women who are pregnant.
WHAT ARE THE STUDIES GENERALLY SHOWING?
In summary, the studies from EMST are generally showing:
Improved maximum expiratory pressures
Improved coughing ability
Increased swallow muscle activity
Improved swallow safety (in some diagnostic groups)
Less deterioration in swallow muscle function, compared to control groups who did not do the exercise or who did a 'sham' exercise
Increased neuroprotective benefits for swallowing and respiratory function
and the major one:
Improved quality of life for those who followed the EMST training protocol
Why should I consider EMST?
If you have recently been diagnosed with a progressive disease such as Multiple Sclerosis, MND/ALS, or Parkinson's Disease, there are a myriad of reasons why you should consider EMST as a treatment. Here are a few of my favourite reasons;
There is a strong evidence base that it works
The programme of training is simple and involves 1/2 hour a day, 5 days a week
You can do it sitting down, so it is good for those with limited mobility
It is cost effective - you buy the device and get set up in the programme, and then continue your 4 or 5 weeks of training with minimal input from the Speech Therapist (so it is cost effective).
Maintenance does not have to be lost and can be continued by only devoting a couple of days a week to the exercise
You are potentially being offered the chance to maintain swallow, speech and respiratory function, over a much longer period of time, than if you didn't complete the exercise at all
Before embarking on any new exercise programme, please be sure to discuss it with your GP/physician first and make sure to disclose your full medical history to any therapist who may be helping you with your EMST programme.
Disclaimer: the above information was produced in good faith and has been summarised from a variety of sources. It is not a substitute for sound medical advice and should not be treated as such. You are encouraged to make your own judgements about whether or not a specific therapy programme will be of benefit to you.