CrossTalk proposal: Training the respiratory muscles does not improve exercise tolerance

• DOI: 10.1113/jphysiol.2012.235408
• Publication Date: 2012-08-01T14:49:53Z
• Authors: Mehul S. Patel; Nicholas Hart; Michael I. Polkey
• Keywords: WALK TEST; Heart Failure; Lung Diseases; Exercise Tolerance; PERFORMANCE; OBSTRUCTIVE PULMONARY-DISEASE; Breathing Exercises; CHRONIC HEART-FAILURE; Respiratory Muscles; INSPIRATORY MUSCLE; Exercise Therapy; 3. Good health; 03 medical and health sciences; 0302 clinical medicine; DIAPHRAGM STRENGTH; ADAPTATIONS; ENDURANCE EXERCISE; Humans; TRIAL

If effective, respiratory muscle training (RMT) is surely the most unfortunate therapy in medicine. Over 35 years have elapsed since seminal work of Leith and Bradley (Leith & Bradley, 1976), yet despite being relatively cheap free side effects, RMT finds limited favour beyond specialist sporting activities remains tool enthusiast. Several caveats require consideration when assessing whether improves exercise tolerance. The first can improve performance healthy humans and, as claimed, a range diseases. In this context, although 0.7% reduction swimming time was not deemed worthwhile, 1.5% (Kilding et al. 2010). contrast, an improvement over 10% may be required to considered worthwhile clinically (Redelmeier 1997). Secondly, tends aspects which are inherent training; i.e. inspiratory pressure generation enhances ability generate pressure, while flow-generating tasks enhance flow (Romer McConnell, 2003). Similarly, two admittedly small studies, improved static mouth but effort-independent measure diaphragm strength (Hart 2001; Verges 2009). These observations do preclude possibility that brain trained; indeed cortical excitability known increased disease (Hopkinson 2004) pulmonary after injury (Sutbeyaz Nevertheless, several arguments support case against general application RMT. First, many trials, there no clear consensus performance. quality studies partly explain this. We reviewed 130 papers for article; only three trials included more than 50 participants, surprising given simplicity safety Of these, (Larson 1999; Correa 2011) showed effect on performance, interpretation findings third were cut (Gething 2004). Some reported outstanding clinical significance with remarkably low participant numbers; example, Dall'Ago colleagues found six minute walk distance (6MWD) by 19% randomising 32 patients heart failure (Dall'Ago 2006); contrast 12 46 ACE inhibition 3 15 β blockers (proven treatments) 6MWD active mainly because improvements following placebo (Fig. 1; Olsson 2005). Mean difference interventional chronic There smaller reporting positive therapy. Reproduced from (2005), permission Oxford University Press. This leads nicely methodological difficulties evaluating RMT: devising adequate placebo. options available investigators (including assessor blinding). Generally, it seems likely genuine intervention will higher benefit either 'doing nothing' or sham requiring resistance minimal repetitions. Thus, appropriate placebo, perceived active, resulted additional conferred (Sonetti 2001). Third, indications recommended enthusiasts, insufficient data showing muscles weak, pertinent examples obstructive (COPD). failure, assessed non-volitionally shows modest degree weakness (Hughes 1999), biopsies reveal evidence type I fibres oxidative enzymes (Tikunov COPD, exhibits similar changes (Levine 1997; Stubbings 2008); importantly exercise-induced dynamic hyperinflation entirely 'weakness' (Polkey 1996). Another objection function correlate poorly. Importantly, Orozco-Levi architectural adaptation intercostal muscles, (Orozco-Levi 1999). another study, endurance COPD patients, without improving any functional (McKeon 1986). investigating expiratory substantially even though classical airway physiology dictates that, increasing force cannot increase flow. Finally, RMT, at least clinically, must compete other proven therapies such rehabilitation (PR), has universally recognised COPD. suggest PR confers peripheral rather lung (which would successful RMT). (the largest perhaps Larson co-workers 1999) meta-analyses, recently Gosselink (2011), show adds PR, thus merely distracting effectiveness PR. As already noted, gains relevant athletes. Discrepancies sports literature probably explained subjective nature tests, diverse regimes, baseline levels presence attributes control groups; context we highlighted study Sonetti displays problems literature. When 5000 m untrained males receiving cardiovascular sham-RMT, correlation between change maximal generated (PImax) (Edwards 2008), suggesting regard performing PImax test behavioural mechanism. It difficult delineate psychological physiological factors studies. Professional swimmers 6 weeks 100 200 1.7% 1.5%, respectively, 400 8.9% relevance unclear those sham-RMT performed better group each percentage did relate Furthermore, elite rigorous swim alone addition resistive revealed differences groups (Mickleborough 2008). burdens controlled breathing hydrostatic pump mean represent unique scenario; however, gives credence benefits specific Lastly, interesting contextual variation concerns participants. expected, involves mostly who calls their training. identified young adults sportsmen (Sperlich 2009; Lomax, neither identified; speculate military professionals scepticism treatment efficacy. Interpreting number sample size, control, double-blinding, balanced characteristics, capacity hazardous. current littered data. A large multicentre, double-blinded randomised trial matched undergoing participants validate before advocating its use group. minimum requirement, expected pharmacological intervention, apply lack reflects view majority physiologists clinicians should advocate therapeutically, enhancement. Readers invited give views accompanying CrossTalk articles issue submitting brief comment. Comments exceed 250 words, maximum references peer publications only. To submit comment, online form centre panel HighWire site. responses been submitted, 'view comments' link visible. All comments moderated add significantly discussion published online-only footnotes articles. posted up publication article, point close authors 'final word'. Questions about call directed Jerry Dempsey [e-mail]. go to: http://jp.physoc.org/letters/submit/jphysiol;590/15/3393 M.I.P. M.S.P.'s contribution article supported NIHR Respiratory Disease Biomedical Research Unit Royal Brompton Harefield NHS Foundation Trust Imperial College London. M.I.P.'s salary part funded N.H. acknowledges financial Department Health via National Institute (NIHR) comprehensive Centre award Guy's St Thomas' partnership King's London Hospital Trust. Please note: publisher responsible content functionality supporting information supplied authors. Any queries (other missing content) corresponding author article.