Effect of inspiratory muscle training on exercise tolerance in asthmatic individuals

Turner LA, Mickleborough TD, McConnell AK, Stager JM, Tecklenburg-Lund S, Lindley MR. Med Sci Sports Exerc. 2011 Nov;43(11):2031-8.
Patients with asthma place a greater demand on their inspiratory muscles, particularly during exercise. The greater workload may increase the risk of fatigue of the inspiratory muscles and therefore exacerbate dyspnea (shortness of breath) and reduce exercise tolerance. It has been hypothesized that strength training the inspiratory muscles in patients with asthma may help decrease the intensity of dyspnea and improve exercise tolerance. Therefore, Turner et al. performed a matched double-blind placebo-controlled trial (investigator and participants did not know who received the treatment) to investigate the effect of 6 weeks of inspiratory muscle training on exercise tolerance and exertional dyspnea in 15 patients with mild to moderate physician-diagnosed asthma. Prior to the intervention the participants attended three sessions: 1) to determine peak power output via maximal incremental cycling test, 2) to familiarize the patient to a constant-power cycle ergometer test, and 3) to conduct the constant-power cycle ergometer test to the limit or tolerance (dyspnea was also assessed during this test using a Borg Rating of Perceived Exertion Scale). After baseline, participants were divided into either an inspiratory muscle training group (n = 7) or a sham group (they performed a fake intervention; n = 8). Participants were matched based on maximal inspiratory pressure (it is unclear how the authors handled having an uneven number of people in each group). Both groups used a pressure threshold training device (provides resistance on inspiration but not expiration) for 6 weeks of training: Training group:  30 dynamic inspiratory efforts twice daily at a pressure threshold load of 50% of maximal inspiratory pressure; Sham group: once daily at a pressure threshold load equivalent to 15% of maximal inspiratory pressure. Compliance was monitored with a sensor in the pressure threshold training device. Overall, the sham group showed no improvement after 6 weeks but the inspiratory training group had a 28% increase in maximum inspiratory pressure and 16% increase in time to the limit of exercise tolerance, compared to baseline. After inspiratory muscle training, perceived dyspnea was decreased by 16%.
Overall, the study demonstrated that inspiratory muscle training “attenuates inspiratory muscle fatigue, reduces the perception of dyspnea, and increases exercise tolerance.”  The authors recommended caution with interventions that decrease the perception of dyspnea because it may cause patients to underestimate the severity of asthmatic exacerbations. This concern may warrant further follow-up in future studies. It will be interesting to see this study replicated in a larger population; particularly with higher-level athletes. This seems to be a logical intervention since we identified a weakness or lack of endurance and we can prescribe a strengthening protocol to address this functional limitation. Inspiratory muscle training may be an interesting adjunct to our care of patients with asthma. Has anyone tried inspiratory muscle training with their patients with asthma?
Written by: Jeffrey Driban

Turner LA, Mickleborough TD, McConnell AK, Stager JM, Tecklenburg-Lund S, & Lindley MR (2011). Effect of inspiratory muscle training on exercise tolerance in asthmatic individuals. Medicine and Science in Sports and Exercise, 43 (11), 2031-8 PMID: 21502887