Respiratory Muscle Training

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Introduction

Respiratory Muscle Training (RMT) can be defined as "a course of therapy consisting of a series of breathing exercises that aim to strengthen the bodies’ respiratory muscles making it easier for people to breathe".

RMT is normally aimed at people who suffer from asthma, bronchitis, emphysema and COPD. However, many people adopt RMT as part of their sports training as this training is designed to strengthen the muscles used for breathing. Studies have shown that regular RMT can increase a person’s endurance during cardiovascular exercise or sports activities such as running and cycling.

When a person is breathing normally, they typically use between 10 to 15 per cent of his or her total lung capacity. With RMT a person can typically increase the amount of lung capacity used. Deeper breathing uses a bit more energy but also allows more oxygen to enter the bloodstream with each breath while strengthening the breathing muscles. Strengthening inspiratory muscles by performing daily breathing exercises for at least six weeks significantly reduces the amount of oxygen these same breathing muscles require during exercise, resulting in more oxygen being available for other muscles.

The evidence

The historical evidence for RMT are presented here:

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 muscle respond to training stimuli in the same manner as the 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 (hypertophy) and muscle thickness have been demonstrated. 
• functional adaptations - improvements in strength, speed, power, endurance performance, peak inspiratory flow, maximal inspiratory and expiratory pressures have been demonstrated.
  

There is evidence that RMT has many beneficial effects in healthy people and has been shown to improve althletic performance.  Results of studies clearly indicate that IMT produces statistically significant improvements in performance but EMT does not.

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 raionale.

How does it work - underlying mechanisms

1. optimisation of blood flow distribution
2. attenuation of central fatigue
3. reduced sense of respiratory and peripheral effort
   

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 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 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, or reduced to just twice a week.

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.  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 rebreathing circuit to prevent hypercapnia.

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).

Implementing RMT

Indications

1. primary indications are people looking to improve exercise tolerance such as athletes or any person, with or without pathological processes, with dyspnoea and/or exercise intolerance
2. main classes of disease, or conditions, where research supports beneficial influence of IMT: respiratory, cardiac, neuromuscular, surgery, healthy ageing.
3. specific conditions where either 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:
   • amyotrophic lateral sclerosis
   • ankylosing spondylosis
   • anorexia nervosa
   • arthritis
   • artificially ventilated patients
   • asthma
   • bronchiectasis
   • cancer
   • cerebral palsy
   • chronic heart failure
   • COPD
   • corticostroid use
   • cystic fibrosis
   • diabetes
   • diaphragm paralysis
   • hypothyroidism
   • kyphoscoliosis
   • multiple sclerosis
   • muscular dystrophies
   • myasthenia gravis
   • obesity
   • obstructive sleep apnoea
   • parkinson's disease
   • 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 too 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 comliance
   • elevated ratio of dead space to tidal volume
   • tachypnoea
   • hypoxaemia
   • hypercapnia
   • poor cough function
   • inability to breathe without aid of mechanical ventilation

Contrandications

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

• history of spontaneous pnuemothorax
• traumatic pneumothorax that has not fully healed
• burst eardrum or other conditions of the eardrum
• unstable ashma with 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
• optimising breathing technique
• diaphragm breathing
• breathing pattern
• secretions

Monitoring progress

assessment of respiratory muscle function

• maximal respiratory pressures
• sniff inspiratory pressure
• peak inspiratory flow rate
• inspiratory muscle endurance

evaluating clinical benefits

Getting Started

• protocol slection
• setting the training load
• repetition failure
• influence of daily activities and exacerbations
• training diaries

Ongoing program

• progression
• maintenance
• incorporating into rehabilitation
• warm up and cool down
• stretching

Resources

• Presentations from the RMT forum at the Centre for Sports Medicine and Human Performance at Brunel University

Recent Related Research (from Pubmed)

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References

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