Respiratory Muscle Training

Original Editor - Rachael Lowe

Top Contributors - Jess Bell, Kim Jackson, Rachael Lowe, Scott Buxton and Vidya Acharya  

Topic Expert - Alison McConnell

Introduction

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Respiratory Muscle Training (RMT) can be defined as a technique that aims to improve the function of the respiratory muscles through specific exercises. Inspiratory Muscle Training (IMT) in particular has been shown to improve respiratory muscle function and might help to reduce dyspnoea on exertion.[1]

RMT is normally aimed at people who have respiratory conditions such as asthma, bronchitis, emphysema and COPD. However, many people adopt RMT as part of their sports training.[2] It has also been found to be beneficial for individuals with other conditions, such as stroke/CVA[3] and Fontan physiology.[4]

RMT may consist of Inspiratory Muscle Training (IMT) or Expiratory Muscle Training (EMT) or a combination of the two.

Responses to RMT

Things that change:

  • effort related responses:
    • breathing effort
    • whole body effort
  • metabolic related responses:
    • respiratory muscle fatigue
    • breathing pattern
    • lactate turnover
    • heart rate
    • oxygen uptake kinetics

These do not change:

  • maximal oxygen uptake
  • maximum lactate threshold

Respiratory muscles respond to training stimuli in the same manner as skeletal muscles i.e. by undergoing adaptations to their structure and function that are specific to the training stimulus.

  • structural adaptations - changes in muscle fibre type, fibre cross-sectional area (hypertrophy) and muscle thickness have been demonstrated[2]
  • functional adaptations - improvements in strength, speed, power, endurance performance, peak inspiratory flow, maximal inspiratory and expiratory pressures have been demonstrated[2].

There is evidence that RMT has many beneficial effects in healthy people[5] and has been shown to improve athletic performance[2].  Results of studies clearly indicate that IMT produces statistically significant improvements in performance but EMT does not.[2] A more recent review has explored the use of RMT in hypoxic conditions.[6] Hypoxic training has become more popular among athletes, but hypoxia related hyperventilation can have negative effects, including respiratory muscle fatigue during prolonged exercise.[6] RMT was found to improve breathing patterns, make respiration more efficient, lower the perception of dyspnoea and improve performance in hypoxic conditions.[6]

The range of pathological conditions in which RMT has been implemented ranges from the obvious (e.g. COPD) to the unexpected (e.g. Diabetes).  The evidence for the use of RMT in these conditions varies widely from conditions where RMT is supported by systematic reviews and meta-analyses (e.g. COPD) to those where there is only theoretical rationale[2].

How does it work - underlying mechanisms

  1. Optimisation of blood flow distribution - when work of breathing increased, blood flow to the legs also decreased. If the work of breathing is decreased, cardiac output reduces, thus blood flood to the legs can increase. It is believed that these changes can be explained by the metaboreflex. Every muscle, including respiratory muscles, have simple nerve endings. When metabolites accumulate, this stimulates these nerve fibres, which sends information to the cardiovascular control centres. This in turn triggers a reflex increase in sympathetic outflow, which causes limb and respiratory vasoconstriction. This reduces blood flow and increases blood pressure, thus explaining the changes in blood flow to the limbs. IMT is thought to affect this because training increases the intensity of inspiratory work required before the reflex is triggered. If the activation of this reflex is abolished or delayed, it is possible to maintain blood flow to the legs for longer, thus enhancing performance.[7]
  2. Attenuation of central fatigue[7]
  3. Reduced sense of respiratory and peripheral effort - by manipulating the work of breathing (ie increasing resistance during training), exercise tolerance is affected. If the work of breathing is increased during training, exercise tolerance is also increased.[7]

Methods of RMT

Training principles

There are three training principles that have been established for all skeletal muscles: overload, specificity and reversibility.  These also apply to respiratory muscles.

  • Overload - to obtain a training response, muscles must be overloaded.  Overload can be applied by altering duration, intensity or frequency. The accepted levels of duration, intensity and frequency used for IMT are:
    • intensity = 50-70 percent (typically yields failure within 30 breaths, or 2-3 mins)
    • duration = 30 breaths
    • frequency = twice daily
  • Specificity - the nature of the training response depends on the type of stimulus delivered.  Muscles, including respiratory muscles, respond to strength training stimuli (high intensity, short duration) by improving strength and endurance training stimuli (low intensity, long duration) by improving endurance.
    • strength - respiratory muscles respond to high-load, low-frequency load with increased strength
    • endurance - endurance training can be achieved with low-load, high-frequency load.  However, it is possible to improve endurance through strength training. Stronger muscles perform any given task at a lower percentage of their maximum capacity than weak muscles do. Strong muscles are therefore able to sustain a given activity for longer periods.
    • lung volume - respiratory muscle length is determined by lung volume, therefore IMT should be conducted over the greatest range of lung volume possible. Start as close as possible to residual volume (maximal exhalation) and end as close as possible to total lung capacity (maximal inhalation).
  • Reversibility
    • detraining - respiratory muscles respond in a similar way to other muscles when the training stimulus is removed. Most of the losses occur within 2-3 months of cessation of training. Endurance is lost before strength. Short periods of detraining (1-2 months) can be accommodated without too much regression of functional gains.
    • maintenance - improvements in inspiratory muscle function can be sustained with training frequency reduced by as much as two thirds - ie 2 days per week in healthy adults and 3 days per week in patients with COPD[8]

Forms of RMT

Training methods can be divided into two types: resistance training and endurance training.

  • Resistance training - inspiratory pressure threshold loading (IPTL) is by far the most commonly used, researched and validated method of RMT[9].  Users breathe via a device (such as the Powerbreathe) that contains a pressure loaded inspiratory valve and an unloaded expiratory flap valve.
  • Endurance training - uses a technique called voluntary isocapnic hyperventilation (VIH) which requires people to maintain high levels of respiration for up to 40 mins.  It utilises a hyperventilation method that employs a partial re-breathing circuit to prevent hypocapnia.

Resistance training is described as the most versatile due to the fact that it is the least time consuming and it results in a dual conditioning response (strength and endurance improvements)[8].

Implementing RMT

Indications

  1. RMT is indicated for anyone who is looking to improve exercise tolerance. This includes individuals with or without pathological processes, those who have dyspnoea and/or reduced exercise tolerance, as well as athletes/sports people.
  2. Research supports the use of IMT in certain classes of disease or conditions. These include: respiratory, cardiac and neuromuscular conditions, as well as around surgery and general ageing.
  3. Specific conditions where IMT has shown clinically significant benefits or there is a rationale for IMT based upon the presence of inspiratory muscle dysfunction and/or abnormal respiratory mechanics include: amyotrophic lateral sclerosis ankylosing spondylosis, anorexia nervosa, arthritis, artificially ventilated patients, asthma, bronchiectasis, cancer, cerebral palsy, chronic heart failure, COPD, corticosteroid use, cystic fibrosis, diabetes, diaphragm paralysis, hypothyroidism, kyphoscoliosis, multiple sclerosis, muscular dystrophies, myasthenia gravis, obesity, obstructive sleep apnoea, Parkinson's, post-polio, pregnancy, pulmonary arterial hypertension, renal failure, sarcoidosis and interstitial lung disease, senescence, spinal cord injury, surgical patients (abdominal and thoracic) ventilator-induced myopathy and failure to wean, ventilatory failure (vulnerability to) vocal cord dysfunction and stridor.
  4. Some specific physiological indicators of inadequate respiratory muscle function:
    • reduced respiratory muscle strength
    • dyspnoea
    • orthopnoea
    • expiratory muscle flow limitation
    • hyperventilation
    • reduced respiratory system compliance
    • elevated ratio of dead space to tidal volume
    • tachypnoea
    • hypoxaemia
    • hypercapnia
    • poor cough function
    • inability to breathe without aid of mechanical ventilation

Contraindications

There have been no reports of adverse event following RMT, however there is a risk of barotrauma-related events[9]. Accordingly, caution should be exercised in the following events:

  • history of spontaneous pneumothorax
  • traumatic pneumothorax that has not fully healed
  • burst eardrum or other conditions of the eardrum
  • unstable asthma with an abnormally low perception of dyspnoea

Precautions

  • Minimise hypercapnia in patients with coronary artery disease
  • May cause ear discomfort in people who have had a recent cold or sinusitis
  • Clinical judgement should be used in individuals who have experienced an acute exacerbation or chest infection
  • Individuals should be cautioned against sharing training equipment

Practical issues

  • Posture - has a role to play in obtaining optimal results. The ideal positions for foundation training are sitting or standing. Recumbent and semi-recumbent postures are known to impair respiratory muscle function and inspiratory muscle function is optimised in the upright position. Once foundation training is complete, training in functional positions can commence. 
  • Optimising breathing technique - choose the right training device, optimise the training stimulus it generates, use a good breathing technique (i.e. diaphragmatic breathing), use a good breathing pattern.
  • Diaphragm breathing - disease related changes to the mechanics of breathing can lead to a reduction in diaphragm mobility.  This, as well as exercise tolerance and breathing pattern, can be improved with a diaphragm breathing training program.  Relearning normal efficient breathing strategies underpins Foundation IMT.
  • Breathing pattern - breathing movements should take place over the largest range possible and maximise recruitment of the inspiratory musculature.
  • Secretions - repeated deep inhalations against an inspiratory load have been found to have been twice as effective as standardised physiotherapy consisting of postural drainage and active cycle of breathing technique.[9]  Individuals, particularly patients with conditions such as bronchiectasis and bronchitis, may experience loosening of secretions following IMT.  Accordingly, people need to be warned of this and advised on appropriate secretion clearance techniques.

Monitoring progress

Progress should be assessed by changes in:

  1. Inspiratory muscle function - ensure that the training regime is stimulating adaptation in inspiratory musculature and that improvements in function are accommodated by increasing training intensity.
  2. Clinical outcomes that result from the former.

 Assessment of respiratory muscle function may utilize: 

  • Maximal respiratory pressures (MIP) - provides a surrogate measure of strength and is the most widely used measure of IMT-induced changes in inspiratory muscle function. It is measured using a clinical apparatus against an occluded airway at a prescribed lung volume.
  • Sniff inspiratory pressure - an alternative to MIP which measures the pressure in the nostril during a maximal sniff.
  • Peak inspiratory flow rate - has been shown to improve in response to moderate IMT training.  Requires a mechanical peak inspiratory flow meter.
  • Inspiratory muscle endurance - there is no standard test for this, but the tests fall into two categories: hyperpnoea tests and inspiratory loaded breathing tests.

The evaluation of clinical benefits will vary enormously between patient populations. The outcome measures selected need to be specific for the clinical population being addressed whilst also being sensitive to the effects of IMT.

Getting Started

IMT starts with Foundation training. Foundation training is underpinned by diaphragmatic breathing and a good breathing pattern.  It takes place for 6 weeks prior to moving on to functional training. 

Foundation training concepts:

  • use a training load of 50-60%of MIP or set intensity to a 30 repetition maximum(30RM), i.e. repetition failure occurs at 30 breaths, using a process of trial and error (repetition failure of the inspiratory muscles is an inability to achieve a satisfying breath).
  • use stretching and warm up to prepare for IMT.
  • inhale against load with maximum effort (as fast as possible).
  • breathe in and out as far as possible during each breath.
  • train twice per day - morning and evening not less than 6 hours apart.
  • increase the training load at least once per week.
  • progress the training by maintaining it at 50-60% of the new MIP or keeping the load at the new 30RM to account for improvement.
  • train to failure in a window between 25-35 breaths per session.
  • keep in mind that at certain times of day, other activities and health status may affect IMT because of residual fatigue.
  • if you suspect that there is residual fatigue of the inspiratory muscles, take a day off.
  • keep an IMT diary.

Ongoing program

  • Progression - functional training can be initiated after 6 weeks of Foundation IMT. It should be undertaken at least 3 days per week and always in tandem with Foundation training which should be undertaken at least 3 days per week.
  • Maintenance - maintenance training can be initiated after 12 weeks of IMT. Reduce frequency to once every other day.
  • Pre-habilitation - implementing IMT prior to whole-body training has been shown to improve the outcome of the whole-body training and can therefore be considered effective rehabilitation.
  • Incorporating into rehabilitation - can be done prior to, during or after a rehabilitation session.
  • Warm up - 2 sets of 30 breaths at 40% MIP with 1 minute of rest between. It should be completed no more than 10 minutes before IMT training.
  • Cool down - aids the clearing of metabolites to help with recovery and adaptation.
  • Stretching - thoracic stretching will reduce any musculoskeletal resistance to inhalation and can result in improvements in chest wall expansion and functional residual capacity therefore increasing the effectiveness of RMT.

Functional training

The role of the respiratory muscles extends beyond their role in driving respiration. They are also a vital component of our postural control and core stabilisation.  This non-respiratory function is pivotal to performance and injury prevention. 

The non-respiratory roles of the respiratory muscles are often brought into conflict with their role in breathing. The external manifestation of this conflict is dyspnoea that is disproportionate to the ventilatory demand of activity. It can also compromise the effectiveness with which the respiratory muscles contribute to their non-respiratory core-stabilising functions.

The objective, therefore, of functional training is to also enhance the core stabilisation role of the respiratory muscles.  In this way, the respiratory function of the respiratory muscles can be optimised to improve core stability.  This is achieved by performing IMT in positions that challenge core stability.

Two approaches can be taken in the selection of exercises for an individual:

  1. use a generic set of around 10 exercises that provides holistic benefits
  2. create a bespoke set of exercises specifically for the individual e.g. tasks that are particularly challenging for a patient, sporting positions or actions used by an athlete.

Underlying principles

  1. Should be preceded by a 6 week period of Foundation IMT and development of good diaphragmatic breathing technique.
  2. Ensure the individual has good technique and exercise form before adding any resistance.
  3. Start by performing each exercise with nothing more than a focus on maintaining, slow, deep diaphragmatic breathing throughout. Then add external resistance to inhalation using an inspiratory muscle training device (IMTD) set on its minimum load.
  4. Gradually increase the load on the IMTD over a period of a few weeks.
  5. Workouts should be preceded by stretching and mobilising exercises.
  6. An individual workout should consist of around 10 exercises.
  7. Exercises should be performed at least 3 times per week.  On other days Foundation IMT should take place.

Sample exercise videos can be viewed at Physiobreathe

Additional Resources

References

  1. Pereira MC, Dacha S, Testelmans D, Gosselink R, Langer D. Assessing the effects of inspiratory muscle training in a patient with unilateral diaphragm dysfunction. Breathe. 2019 Jun 1;15(2):e90-6.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 McConnell, A. Functional benefits of respiratory muscle training. Chapter 4 in: Respiratory Muscle Training: Theory and Practice. Elsevier, 2013.
  3. Menzes KKP, Nascimento, LR, Ada L, Polese, JC, Avelino PR, Teixeira-Salmera, LF. Respiratory muscle training increases respiratory muscle strength and reduces respiratory complications after stroke: a systematic review. Journal of Physiotherapy. 2016; 62(3): 138-44.
  4. Wu FM, Opotowsky AR, Denhoff ER, Gongwer R, Gurvitz MZ, Landzberg MJ et al. A Pilot Study of Inspiratory Muscle Training to Improve Exercise Capacity in Patients with Fontan Physiology. Semin Thorac Cardiovasc Surg. 2018; 30(4):462-469.
  5. Illi SK, Held U, Frank I, Spengler CM. Effect of respiratory muscle training on exercise performance in healthy individuals: a systematic review and meta-analysis. Sports Med. 2012 Aug 1;42(8):707-24.
  6. 6.0 6.1 6.2 Alvarez-Herms J, Julia-Sanchez S, Corbi F, Odriozola-Martinez A, Burtscher M. Putative role of respiratory muscle training to improve endurance in hypoxia: A review. Front Physiol. 2018; 9
  7. 7.0 7.1 7.2 McConnell, A. Inspiratory muscle training: history and putative mechanisms. Frontiers in Sport and Exercise Science and Medicine Seminar on inspiratory muscle training, Centre for Sports Medicine and Human Performance, Brunel University, April 2013
  8. 8.0 8.1 McConnell, A. Methods of respiratory muscle training. Chapter 5 in: Respiratory Muscle Training: Theory and Practice. Elsevier, 2013.
  9. 9.0 9.1 9.2 McConnell, A. Implementing respiratory muscle training. Chapter 6 in: Respiratory Muscle Training: Theory and Practice. Elsevier, 2013.
  10. McConnell, A., Romer, L., Ross, E. and Jolley, C. Frontiers in Sport and Exercise Science and Medicine Seminar on inspiratory muscle training, Centre for Sports Medicine and Human Performance, Brunel University, April 2013