ORIGINAL ARTICLE Acute effects of photobiomodulation therapy applied to respiratory muscles of chronic obstructive pulmonary disease patients: a double-blind, randomized, placebo-controlled crossover trial Guilherme Henrique Martins de Souza 1 & Cleber Ferraresi 2 & Marlene Aparecida Moreno 3 & Bruna Varanda Pessoa 1 & Ana Paula Moraes Damiani 1 & Vinicius Gasparotto Filho 1 & Giovanny Viegas dos Santos 1 & Antonio Roberto Zamunér 4 Received: 1 August 2019 /Accepted: 12 September 2019 # Springer-Verlag London Ltd., part of Springer Nature 2019 Abstract To investigate the effects of photobiomodulation applied to respiratory muscles on lung function, thoracoabdominal mobility, respiratory muscle strength, and functional capacity in COPD patients. This is a randomized double-blind crossover clinical trial. Twelve male COPD patients participated in the study. Participants were randomly allocated to receive two photobiomodulation sessions, 1 week apart: (1) an effective photobiomodulation session applied at the main respiratory muscles by means of a cluster with 69 light-emitting diodes (LEDs), containing 35 red (630 ± 10 nm; 10 mW; 0.2 cm 2 ) and 34 near-infrared (830 ± 20 nm; 10 mW; 0.2 cm 2 ) LEDs and (2) a sham photobiomodulation session, following the same procedures without emitting light. The primary outcomes were pulmonary function (spirometric indexes); thoracoabdominal mobility (cirtometry); respiratory muscle strength (maximal respiratory pressures), assessed at three moments: (1) baseline, (2) 1 h after intervention, and (3) 24 h after intervention; and the functional capacity, assessed by the 6-min walk test (6MWT) at baseline and 24 h after intervention. No significant interactions were found for spirometric variables, maximal respiratory pressures, and cirtometry. However, there was a Time × Condition interaction (F = 18.63; p = 0.001; η 2 p = 0.62) in the walked distance on the 6MWT, with a significant increase after photobiomodulation intervention (p < 0.01) compared with the baseline. Photobiomodulation applied to respiratory muscles was effective in improving acute functional capacity in COPD patients. To the best of our knowledge, this is the first study assessing the effects of photobiomodulation applied to respiratory muscles in patients with COPD. Keywords Physical therapy . Low-level light therapy . Phototherapy . Respiratory function tests . 6-min walk test Abbreviations 6MWT 6-Minute walk test COPD Chronic obstructive pulmonary disease FEV1 Forced expiratory volume at 1 s LEDs Light-emitting diodes MEP Maximal expiratory pressure MIP Maximal inspiratory pressure PBMT Photobiomodulation therapy Introduction Chronic obstructive pulmonary disease (COPD) is character- ized by persistent and progressive airflow limitation resulting from an abnormal inflammatory response of the airways and lungs, usually due to the inhalation of harmful particles [1]. Several extrapulmonary manifestations and systemic alter- ations associated with COPD directly influence the course and prognosis of the pathology [2]. Musculoskeletal dysfunction is one of these, limiting the functional capacity, health, and quality of life of these patients [3]. It has also been demon- strated that musculoskeletal impairment is indicative of poor * Antonio Roberto Zamunér beto.zam@gmail.com 1 Pró-Reitoria de Pesquisa e Pós-Graduação, Universidade do Sagrado Coração, São Paulo, SP, Brazil 2 Post-graduation Program in Biomedical Engineering, Universidade Brasil, São Paulo, Brazil 3 Post-graduation Program in Human Movement Sciences, Methodist University of Piracicaba (UNIMEP), Piracicaba, SP, Brazil 4 Departamento de Kinesiología, Laboratorio de Investigación Clínica en Kinesiología, Universidad Católica del Maule, Avenida San Miguel 3605, Talca, Maule, Chile Lasers in Medical Science https://doi.org/10.1007/s10103-019-02885-3