It is known that respiratory muscles undergo adaptation in response to overload stimuli during exercise training in stable COPD patients, thus resulting in significant increase of respiratory muscle function as well as the individual’s improvements. The present article reviews the most updated evidence with regard to the use of respiratory muscle training (RMT) methods in COPD patients. Basically, three types of RMT (resistive training, pressure threshold loading, and normocapnic hyperpnea) have been reported. Frequency, duration, and intensity of exercise must be carefully considered for a training effect. In contrast with the plentitude of existing data inherent to inspiratory muscle training (IMT), literature is still lacking in showing clinical and physiological studies related to expiratory muscle training (EMT). In particular, while it seems that IMT is slightly superior to EMT in providing additional benefits other than respiratory muscle function such as a reduction in dyspnea, both the effects and the safety of EMT is still to be definitively elucidated in patients with COPD.
PMCID: PMC2692111 PMID: 18044062

PURPOSE: To determine the effect of inspiratory muscle training (IMT) (alone or combined with exercise and/or pulmonary rehabilitation) and compare with other rehabilitation interventions among adults with chronic obstructive pulmonary disease (COPD).
METHODS: We conducted a systematic review, using Cochrane Collaboration protocol. We included randomized controlled trials, published in English, comparing IMT or combined IMT and exercise/pulmonary rehabilitation with other rehabilitation interventions among adults with COPD. Abstracts were reviewed independently by 2 investigators to determine study eligibility up to December 2005. Data were abstracted and methodological quality of included studies was assessed.
RESULTS: A total of 156 additional articles were retrieved. Two new studies met the inclusion criteria and were included with 16 studies in the original review. Results highlight updated subgroup analyses comparing (1) IMT versus exercise and (2) combined IMT and exercise versus exercise alone. Fourteen meta-analyses were performed for outcomes of inspiratory muscle strength, exercise tolerance, and quality of life. Results showed significant improvements in maximum inspiratory pressure and maximum exercise tidal volume favoring combined IMT and exercise compared with exercise alone.
CONCLUSIONS: Performing a combination of IMT plus exercise may lead to significant improvements in inspiratory muscle strength and one outcome of exercise tolerance for individuals with COPD.
PMID: 18360190 DOI: 10.1097/01.HCR.0000314208.40170.00

The purpose was to update an original systematic review to determine the effect of inspiratory muscle training (IMT) on inspiratory muscle strength and endurance, exercise capacity, dyspnea and quality of life for adults with chronic obstructive pulmonary disease (COPD). The original MEDLINE and CINAHL search to August 2003 was updated to January 2007 and EMBASE was searched from inception to January 2007. Randomized controlled trials, published in English, with adults with stable COPD, comparing IMT to sham IMT or no intervention, low versus high intensity IMT, and different modes of IMT were included. Nineteen of 274 articles in the original search met the inclusion criteria. The updated search revealed 17 additional articles; 6 met the inclusion criteria, all of which compared targeted, threshold or normocapneic hyperventilation IMT to sham IMT. An update of the sub-group analysis comparing IMT versus sham IMT was performed with 10 studies from original review and 6 from the update. Sixteen meta-analyses are reported. Results demonstrated significant improvements in inspiratory muscle strength (PI(max), PI(max) % predicted, peak inspiratory flow rate), inspiratory muscle endurance (RMET, inspiratory threshold loading, MVV), exercise capacity (Ve(max), Borg Score for Respiratory Effort, 6MWT), Transitional Dyspnea Index (focal score, functional impairment, magnitude of task, magnitude of effort), and the Chronic Respiratory Disease Questionnaire (quality of life). Results suggest that targeted, threshold or normocapneic hyperventilation IMT significantly increases inspiratory muscle strength and endurance, improves outcomes of exercise capacity and one measure of quality of life, and decreases dyspnea for adults with stable COPD.
PMID: 18708282 DOI: 10.1016/j.rmed.2008.07.005

Respiratory rehabilitation is known to improve outcomes in patients with chronic obstructive pulmonary disease (COPD). The question addressed in the present review is whether these beneficial effects are related to improvements in inspiratory muscle function. Respiratory muscle fatigue often did not occur during exercise in patients with COPD, since exercise limitation usually occurred when significant force reserve in the inspiratory muscles was still present. Notwithstanding, a number of observations may provide indirect evidence that respiratory muscle fatigue may occur during exercise. Some evidence is present that, in normal humans, whole body exercise training improved inspiratory muscle endurance, but no studies are available in patients with COPD. Animal studies invariably demonstrated that exercise training increased the number of oxidative fibers and oxidative enzyme activity in inspiratory muscles. These effects, however, were considerably smaller than the effects found on peripheral muscles with similar fiber composition. Clear evidence indicated that inspiratory muscle training (IMT) improved inspiratory muscle function. Two large meta-analyses indicated that, if the training load was properly controlled, IMT alone or combined with general exercise reconditioning improved inspiratory muscle strength and endurance and dyspnea. The combination did not result in greater improvements in functional exercise capacity. Animal studies and one patient study confirmed the occurrence of structural remodeling of the inspiratory muscles in response to IMT. The final question is whether improvements in inspiratory muscle function produced by IMT lead to improved outcomes in COPD. In all five studies in which training load was adequately controlled, a significant reduction of dyspnea during activities of daily living was found. Eight randomized studies examined the effects of the combination. Greater improvements in exercise capacity were only found in three studies, and none showed a greater reduction in dyspnea.
PMID: 19342436 DOI: 10.1152/japplphysiol.91459.2008

Inspiratory muscles have been specifi cally targeted for training patients with chronic obstructive pulmonary disease (COPD). So far, the rationale for training has been questioned.
Although inspiratory muscle strength is low in most of these patients, mainly because of the mechanical disadvantage due to hyperinfl ation, respiratory muscles are likely to adapt to the chronically imposed work of breathing [1] , and the diaphragmatic contractile fatigue is rarely observed even during strenuous exercise in stable disease [2] . On the one hand, respiratory muscles, unlike the peripheral muscles, apparently do not to suffer from deconditioning, and a training intervention does not appear justified on this basis. On the other hand, the work of the diaphragm is clearly increased during exercise [3] , thus leading to perception of ‘ diffi cult inspiration ’, ‘ shallow breathing ’ or ‘ unrewarded inspiration ’ [4] , especially in some COPD patients whose respiratory muscle adaptation may be insufficient.
Therefore, if inspiratory muscle training (IMT) is able to increase the maximal inspiratory muscle pressure(PImax ), and to change the structure of these muscles, it seems reasonable to expect that symptoms will be reduced while exercising, thus turning these effects into a functional benefi t. These positive effects have been confirmed in COPD patients with inspiratory muscle weakness by a recent systematic review [5] . IMT programs require regular supervision but are relatively inexpensive and can be conducted at home. One study investigating the long-term effect of IMT suggested that benefits wear off rapidly when training is discontinued [6] . Whether training conducted with appropriate load also translates into increased exercise tolerance and better quality of life is still unclear, thus making the evidence-based guidelines [7, 8]to conclude that IMT should not be a routine component in the rehabilitation programs.
In this issue of Respiration , Weiner et al. [9]pointed out a practical problem in the management of COPD patients showing weakness of their inspiratory muscles. This may cause, in turn, the inability to generate adequate fl ow to assure lung deposition when using dry powder inhalers (DPIs), which are commonly prescribed to deliver bronchodilators to these patients. Bio availability is predictive of the clinical effect of the inhaled drug [10]and peak inspiratory fl ow (PIF) measurements refl ect the patient’s ability to properly inhale the drug.
Authors have found that almost 20% of the most compromised patients (staged according to the forced expiratory volume in 1 s) are not able to generate enough flow to assure proper inhalation (and therefore deposition) from one of the most popular and commonly used devices (Turbohaler) and that, in addition, PIF values correlate with a patient’s PImax [9] . Since the maximal inspiratory fl ow, at a given volume, depends both on airway resistance and on strength as well as the speed of shortening of the inspiratory muscles [11] , it is reasonable that IMT should enable those COPD patients with respiratory muscle weakness to assure adequate drug deposition in their lungs and, therefore, bronchodilation. Indeed, Weiner et al. [9]have demonstrated that IMT at adequate load signifi cantly increased PImax and PIF in weak COPD patients. This problem, outside a clinical trial, may involve about one third of COPD patients [12] , i.e. these subjects are unlikely to benefi t from most part of the drug delivered by means of DPIs at home. Finally, the experience gained by Weiner et al. [9]shows that training inspiratory muscles allows patients to use any type of DPI and suggests that ‘ the systematic measurement of PIF and PI max’ in the most compromised COPD patients may warrant a proper way to improve breathing and consequently drug inhalation.
PMID: 16549941 DOI: 10.1159/000091529