Vol.:(0123456789)1 3 European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 https://doi.org/10.1007/s00405-020-06202-5 REVIEW ARTICLE Does the external nasal dilator strip help in sports activity? A systematic review and meta‑analysis Ricardo Reis Dinardi1  · Carlos Henrique Santos Ferreira1 · Giordani Santos Silveira2 · Vânia Eloisa de Araújo Silva2 · Cássio da Cunha Ibiapina1 · Cláudia Ribeiro de Andrade1 Received: 30 March 2020 / Accepted: 8 July 2020 / Published online: 18 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract Background Numerous studies have shown that the external nasal dilator (END) increases the cross sectional area of the nasal valve, thereby reducing nasal resistance, transnasal inspiratory pressure, stabilizing the lateral nasal vestibule, and preventing its collapse during final inhalation. Objectives Our objective was to carry out a systematic review of the literature and meta-analysis on the effects of the END during physical exercise. Methods After selecting articles in the PubMed, Cochrane Library and EMBASE databases, 624 studies were identified. However, after applying the inclusion and exclusion criteria, 19 articles were considered eligible for review. Results Those studies included in the meta-analysis, the maximal oxygen uptake (VO2max.) outcome was assessed in 168 participants in which no statistically significant difference was found, MD (95% CI) = 0.86 [− 0.43, 2.15], p = 0.19, and I2 = 0%. The heart rate (HR) outcome was assessed in 138 participants in which no statistically significant difference was found, MD (95% CI) = 0.02 [− 3.19, 3.22], p = 0.99, and I2 = 0%. The rating of perceived exertion (RPE) outcome was assessed in 92 participants in which no statistically significant difference was found, MD (95% CI) = − 0.12 [− 0.52, 0.28], p = 0.56, and I2 = 27%. Conclusions The external nasal dilator strip showed no improvement in VO2max., HR and RPE outcomes in healthy indi- viduals during exercise. Keywords External nasal dilator · Nasal valve · Nasal resistance · Physical exercise · Performance Introduction The anterior portion of the nasal cavities, from the nostril to the nasal valve (NV), is the region of greatest nasal resist- ance to airflow and of the utmost importance in nasal physi- ology [1]. Nasal dilators are devices that expand the cross-sectional area of the NV in an attempt to improve airflow. There are several dilators currently available on the market that can act internally or externally in the NV region [2, 3]. Nasal dilators may be recommended for the relief of nasal congestion, allergic reaction, snoring, deviated nasal septum, obstructions that occur in the presence of certain diseases and to improve performance during physical exer- cise. Given that the END has an impact on maximal oxygen uptake [4–6], reduces nasal airflow resistance [7, 8], delays the onset of breathing through the mouth during aerobic exercise [9], reduces dyspnea and ventilation during exercise [4, 5, 10], among other parameters, it is possible that the dilators affect performance, particularly in aerobic exercise. However, it should be highlighted that although they are used, these devices have limited scientific support and need to be further analyzed regarding their effectiveness [2, 11, 12]. In a recent systematic review aimed at classifying dila- tors based on their mechanism of action, Kiyohara et al. [2] found a variety of devices available. The external (END) * Ricardo Reis Dinardi dinardi06@hotmail.com 1 Department of Pediatrics, Faculty of Medicine, Federal University of Minas Gerais-Post Graduate Program in Health Sciences, Rua Sertões 100 – Ap 201 – Prado, Belo Horizonte, MG CEP: 30411-164, Brasil 2 Department of Dentistry, Pontifical Catholic University of Minas Gerais-Post Graduate Program in Orthodontics, Belo Horizonte, MG, Brasil http://orcid.org/0000-0002-7457-2939 http://crossmark.crossref.org/dialog/?doi=10.1007/s00405-020-06202-5&domain=pdf 1308 European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 and internal (IND) nasal dilators are those that have been studied the most. The study undertaken by Griffin et al. [4] was one of the first to evaluate the effectiveness of the external nasal dilator in healthy adult athletes. Using a randomized, double-blind, controlled sample with placebo group, a significant drop in the rating of perceived exertion, heart rate, ventilation and maximal oxygen uptake was noted when compared with the placebo group. In addition, acoustic rhinometry was used to measure the area of the NV and, with the END, a significant increase in the NV was observed at rest. On the other hand, studies carried out by Thomas et al. and Overend et al. did not find positive results in healthy adult male and female athletes who used the END [13, 14]. Considering the conflicting data from the research per- formed, the objective of this study was to undertake a review of the literature to date on the possible effects of the external nasal dilator on performance in physical exercise. Materials and method The protocol for this systematic review and meta-analysis followed recommendations from the Cochrane Collabo- ration Handbook and was based on the Preferred Report- ing Items for Systematic Reviews and Meta-Analysis Pro- tocols (PRISMA-P) [15, 16]. This systematic review and meta-analysis are registered in the International Regis- ter of Systematic Reviews (PROSPERO) under number CRD42019112793 (https ://www.crd.york.ac.uk/prosp ero/). According to the PICO approach, the inclusion criteria were selected by (a) population: adolescent and adult individuals of both sexes aged between 12 and 35 years; (b) interven- tion: external nasal dilator (Fig. 1); (c) comparison: absence of an external nasal dilator, internal nasal dilator, placebo and medication; (d) outcomes (performance measurements): maximal oxygen uptake (VO2max.), heart rate (HR) and rat- ing of perceived exertion (RPE). Eligibility criteria Only randomized controlled clinical trials (RCTs) and non-randomized controlled clinical trials (NRCTs) were included. The exclusion criteria were: (a) evaluation of the external dilator’s effect on sleep, (b) snoring, pregnancy, nasal congestion, any type of neoplasia and individuals with deviated septum, (c) review studies, and (d) summaries of congresses. Databases and search strategy The electronic databases MEDLINE (via PubMed), Cochrane Controlled Trials Databases (CENTRAL) and EMBASE were searched with no language or date restric- tions. Furthermore, a manual search was undertaken of the references from all the studies included. The following terms and keywords were used with the Boolean operators “AND” and “OR” respecting the specificity of each electronic data- base: “nasal obstruction”, “nasal blockage”, “nasal airway obstruction”, “external nasal dilator”, “external nasal dila- tor strip”, “exercise”, “physical exercise”, "aerobic exer- cise", "exercise training" and “sports”. Selection of studies After excluding duplicate studies, two researchers inde- pendently selected the studies according to the eligibility criteria, by first reading the titles and abstracts before then analyzing the texts in full. Disagreements on the inclusion and exclusion of certain studies were resolved by a third researcher. Data extraction and risk of bias assessment Data on authorship and year of publication, intervention and comparison, sample, evaluated parameters and results from the selected studies were extracted and organized in Table 1. Fig. 1 External nasal dilator https://www.crd.york.ac.uk/prospero/ 1309European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 Ta b le 1 C h ar ac te ri st ic s o f th e in cl u d ed s tu d ie s S tu d y In te rv en ti o n C o n tr o l N O u tc o m e d es cr ip ti o n In te rv en ti o n r es u lt s C o n tr o l re su lt s p v al u e V O 2 m ax T ro cc h io 1 9 9 5 E N D : B re at h -R ig h t® W it h o u t N D 1 6 M V O 2 m ax ( m l/ k g /m in ) E N D = 4 3 .8 ± 6 .5 C o n tr o l = 4 4 .0 ± 6 .7 B et w ee n 0 .2 6 – 0 .8 4 G ri ffi n 1 9 9 7 E N D /L I an d E N D /H I P la ce b o ( st ri p w it h o u t el as ti c st ri p s in t h e ce n te r) 3 0 ( 2 0 M a n d 1 0 F ) V O 2 ( L /m in ) E N D /L I= 1 .2 5 4 E N D /H I= 1 .8 6 1 P la ce b o /L I = 1 .3 9 5 P la ce b o /H I= 2 .0 4 p < 0 .0 5 C as e 1 9 9 8 E N D : B re at h -R ig h t® P la ce b o a n d w it h o u t N D 9 M V O 2 m ax ( m l/ k g /m in ) E N D = 4 8 .2 ± 6 .1 C o n tr o l = 4 8 .0 ± 4 .4 N R C h in ev er e 1 9 9 9 E N D : B re at h -R ig h t® N o se ( N ), M o u th ( M ), M o u th + N o se ( M N ), M o u th + N o se + E N D (M N E N D ) 1 0 ( 4 M a n d 6 F ) V O 2 m ax ( m l/ k g /m in ) E N D = 4 5 .8 ± 1 3 .5 N = 4 5 .5 ± 1 0 .5 , M = 4 8 .1 ± 1 3 .8 , M N = 4 8 .4 ± 1 1 .8 , M N E N D = 5 0 .9 ± 1 1 .1 p > 0 .0 5 B ak er 1 9 9 9 E N D ( b ra n d d id n o t m en ti o n ed ) P la ce b o ( fa k e n as al d il at o r) 1 0 ( 3 M a n d 7 F ) V O 2 (L /m in ) N o t m en ti o n ed N o t m en ti o n ed – O ’K ro y 2 0 0 0 E N D : B re at h e R ig h t® P la ce b o a n d m o u th b re at h in g ( M B ) 1 5 ( 5 M a n d 1 0 F ) V O 2 ( L /m in ) E N D = 3 .0 4 ± 0 .9 4 P la ce b o = 3 .1 2 ± 1 .0 6 M B = 3 .1 2 ± 1 .1 N R O ’K ro y 2 0 0 1 E N D : (b ra n d d id n o t m en ti o n ed ) P la ce b o ( fa k e N D ) 1 4 ( 3 M a n d 1 1 F ) P ea k V O 2 m ax (m L /k g / m in ) an d 7 0 % V O 2 m L /k g /m in E N D p ea k V O 2 = 3 3 .0 ± 6 .7 E N D 7 0 % V O 2 = 2 4 .3 ± 4 .2 P la ce b o p ea k V O 2 = 3 3 .4 ± 6 .9 P la ce b o 7 0 % V O 2 = 2 3 .9 ± 4 .6 p > 0 .0 5 T o n g 2 0 0 1 a E N D : (b ra n d d id n o t m en ti o n ed ) W it h o u t N D 8 M V O 2 m ax ( m l/ k g /m in ) E N D = 3 8 .9 ± 3 .1 C o n tr o l = 3 8 .5 ± 2 .6 p > 0 .0 5 F (2 ,1 6 ) = 0 .5 2 T o n g 2 0 0 1 b E N D : (b ra n d d id n o t m en ti o n ed ) O ro n as al b re at h in g an d P la ce b o ( fa k e n as al d il at o r) 9 M V O 2 ( m l/ k g /m in ) N o t m en ti o n ed N o t m en ti o n ed p > 0 .0 5 F (2 ,1 6 ) = 0 .5 2 T h o m as 2 0 0 1 E N D : B re at h -R ig h t® P la ce b o ( fa k e n as al d il at o r) a n d W it h o u t n as al d ev ic e 1 4 ( 8 M a n d 6 F ) V O 2 (m l/ k g /m in ) d u r- in g r ec o v er y f ro m an ae ro b ic e x er ci se E N D a ft er 5 m in u te s = 1 2 .7 ± 3 .8 E N D a ft er 1 0 m in u te s = 5 .8 ± 1 .9 P la ce b o a ft er 5 m in - u te s = 1 2 .3 ± 3 .4 P la ce b o a ft er 1 0 m in - u te s = 5 .7 ± 1 .7 W it h o u t E N D a ft er 5 m in u te s = 1 2 .9 ± 3 .7 W it h o u t E N D a ft er 1 0 m in u te s = 5 .7 ± 1 .6 – N es p er ei ra 2 0 0 4 E N D : B re at h -R ig h t® W it h o u t N D 7 M V O 2 ( m l/ k g /m in ) 3 in te n si ti es E N D i n te n si ty 2 , 4 an d 7 , re sp ec ti v el y : 1 .5 8 , 1 .5 7 a n d 2 .5 3 . (d ec re as e) N R p < 0 .0 5 M ac fa rl an e an d F o n g 2 0 0 4 E N D : B re at h -R ig h t® P la ce b o ( fa k e N D ) an d W it h o u t N D 3 0 M ( ad o le sc en ts ) V O 2 m ax ( m l/ k g /m in ) E N D i m p ro v ed 3 .2 % an d 2 .9 % c o m p ar ed to t h e co n tr o l co n d i- ti o n a n d p la ce b o , re sp ec ti v el y. N R p = 0 .0 3 7 ( co n tr o l) a n d p = 0 .0 1 8 ( p la ce b o ) 1310 European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 Ta b le 1 (c o n ti n u ed ) S tu d y In te rv en ti o n C o n tr o l N O u tc o m e d es cr ip ti o n In te rv en ti o n r es u lt s C o n tr o l re su lt s p v al u e N u n es 2 0 1 1 E N D : B re at h -R ig h t® P la ce b o ( fa k e N D ) an d W it h o u t N D 9 M 6 0 % V O 2 (m l/ k g /m in ) N R N R p > 0 .0 5 D in ar d i 2 0 1 3 E N D : C le ar P as sa g e® P la ce b o ( fa k e N D ) 4 8 ( 1 7 M a n d 3 1 F ) V O 2 m ax ( m l/ k g /m in ) E N D = 5 3 .0 ± 4 ,2 P la ce b o = 5 1 .2 ± 5 .5 p = 0 .0 0 1 A d am s 2 0 1 7 E N D : B re at h R ig h t® T u rb in e® i n te rn al N D an d W it h o u t N D 1 5 M W .V O 2 (w h er e W i s th e p re sc ri b ed w at t- ag e fo r th e st ag e) . S ta n d ar d iz ed w ar m - u p a t 3 0 , 5 0 a n d 7 0 % o f fa m il ia ri za ti o n m ea n t im e tr ia l p o w er o u tp u t E N D ( W .V O 2 ) 3 0 % = 5 3 .2 ± 7 .8 E N D ( W .V O 2 ) 5 0 % = 6 4 .2 ± 8 .5 E N D ( W .V O 2 ) 7 0 % = 6 8 .1 ± 7 .9 In t. ( W .V O 2 ) 3 0 % = 5 3 .9 ± 5 .8 ; n t. ( W .V O 2 ) 5 0 % = 6 5 .7 ± 5 .6 ; In t. ( W .V O 2 ) 7 0 % = 6 9 .9 ± 3 .5 W it h o u t N D ( W .V O 2 ) 3 0 % = 5 3 .9 ± 7 .2 W it h o u t N D ( W .V O 2 ) 5 0 % = 6 5 .3 ± 7 .6 W it h o u t N D ( W .V O 2 ) 7 0 % = 6 9 .1 ± 6 .5 (W .V O 2 ) 3 0 % = 0 .8 6 (W .V O 2 ) 5 0 % = 0 .6 7 (W .V O 2 ) 7 0 % = 0 .7 4 O tt av ia n o 2 0 1 7 E N D : B re at h R ig h t® N D M as te r- ai d R o ll - fl ex ® a n d W it h o u t N D 1 3 ( 8 M a n d 5 F ) V O 2 m ax (m l/ k g /m in ) an d N as al V O 2 ( m l/ k g /m in ) E N D = 5 5 .2 ± 6 .6 a n d 5 1 .0 ± 5 .9 4 ( re sp ec - ti v el y ) M as te r- ai d R o ll -fl ex ® = 5 5 .3 ± 7 .4 a n d 5 1 .8 ± 6 .8 ( re sp ec - ti v el y ) W it h o u t N D = 5 4 .3 ± 7 .0 a n d 4 9 .3 ± 6 .6 (r es p ec ti v el y ) p = 0 .8 2 a n d p < 0 .0 0 1 (r es p ec ti v el y ) D in ar d i 2 0 1 7 E N D : C le ar P as sa g e® P la ce b o ( fa k e N D ) 3 5 M ( ad o le sc .) V O 2 m ax (m l/ k g /m in ) E N D = 3 6 .1 ± 9 .1 P la ce b o = 3 4 .0 ± 9 .2 N R H R G ri ffi n 1 9 9 7 E N D /L I an d E N D /H I P la ce b o ( st ri p w it h o u t el as ti c st ri p s in t h e ce n te r) 3 0 ( 2 0 M a n d 1 0 F ) H R ( b ea ts /m in ) E N D /L I = 1 1 7 E N D /H I = 1 4 5 P la ce b o /L I = 1 2 3 P la ce b o /H I = 1 5 0 L I = 0 .0 6 H I = p < 0 .0 5 C as e 1 9 9 8 E N D : B re at h -R ig h t® P la ce b o a n d w it h o u t N D 9 M H R ( b ea ts /m in ) E N D = 1 8 7 ± 1 1 P la ce b o = 1 8 1 ± 1 5 C o n tr o l = 1 8 5 ± 1 2 N R B ak er 1 9 9 9 E N D ( b ra n d d id n o t m en ti o n ed ) P la ce b o ( fa k e n as al d il at o r) 1 0 ( 3 M a n d 7 F ) H R ( b ea ts /m in ) N o t m en ti o n ed N o t m en ti o n ed – C h in ev er e 1 9 9 9 E N D : B re at h -R ig h t® N o se ( N ), M o u th ( M ), M o u th + N o se ( M N ), M o u th + N o se + E N D (M N E N D ) 1 0 ( 4 M a n d 6 F ) M ax im u m H R ( b ea ts / m in ) E N D = 1 8 5 ± 1 0 N = 1 8 1 ± 9 * , M = 1 9 2 ± 7 , M N = 1 9 1 ± 5 , M N E N D = 1 9 1 ± 7 * p < 0 .0 5 O ’K ro y 2 0 0 0 E N D : B re at h e R ig h t® P la ce b o a n d m o u th b re at h in g ( M B ) 1 5 ( 5 M a n d 1 0 F ) H R ( b ea ts /m in ) N o t m en ti o n ed N o t m en ti o n ed - 1311European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 Ta b le 1 (c o n ti n u ed ) S tu d y In te rv en ti o n C o n tr o l N O u tc o m e d es cr ip ti o n In te rv en ti o n r es u lt s C o n tr o l re su lt s p v al u e O v er en d 2 0 0 0 E N D : B re at h R ig h t® W it h o u t N D ( co n tr o l) 1 9 M H R ( b ea ts /m in ) in 3 co n d it io n s: 1 ) th e tr an si ti o n b et w ee n w al k in g a n d j o g g in g , 2 ) th e ti m e w h en t h e su b je ct i n d ic at ed t h e d es ir e to r em o v e th e m o u th g u ar d a n d 3 ) v o li ti o n al f at ig u e. E N D H R 1 ) = 1 3 5 ± 1 4 E N D H R 2 ) = 1 7 5 ± 1 6 E N D H R 3 ) = 1 8 9 ± 8 C o n tr o l H R 1 ) = 1 3 2 ± 1 3 C o n tr o l H R 2 ) = 1 7 1 ± 1 7 C o n tr o l H R 3 ) = 1 8 7 ± 9 N R T h o m as 2 0 0 1 E N D : B re at h -R ig h t® P la ce b o ( fa k e n as al d il at o r) a n d W it h o u t n as al d ev ic e 1 4 ( 8 M a n d 6 F ) H R ( b ea ts /m in ) E N D a ft er 5 m in u te s = 1 0 9 .6 ± 2 9 .6 E N D a ft er 1 0 m in u te s = 9 1 .2 ± 2 4 .9 P la ce b o a ft er 5 m in - u te s = 1 0 9 .5 ± 2 9 .1 P la ce b o a ft er 1 0 m in - u te s = 9 3 .3 ± 2 5 .2 W it h o u t E N D a ft er 5 m in u te s = 1 0 9 .7 ± 2 8 .7 W it h o u t E N D a ft er 1 0 m in u te s = 9 2 .4 ± 2 3 .9 – B o u rd in 2 0 0 2 E N D : B re at h -R ig h t® W it h o u t N D a n d n o n as al v en ti la ti o n (u si n g a n o se c li p ) 1 0 M H R ( b ea ts /m in ) E N D = 1 7 3 ± 8 W it h o u t N D = 1 7 3 ± 7 N o se c li p = 1 7 2 ± 7 p = 0 .9 9 N es p er ei ra 2 0 0 4 E N D : B re at h -R ig h t® W it h o u t N D 7 M H R ( b ea ts /m in ) 3 in te n si ti es E N D i n te n si ty 4 a n d 7 , re sp ec ti v el y : 6 .7 an d 5 .0 9 ( in cr ea se ); E N D i n te n si ty 2 : 1 .3 6 ( d ec re as e) N R p > 0 .0 5 N u n es 2 0 1 1 E N D : B re at h -R ig h t® P la ce b o ( fa k e N D ) an d W it h o u t N D 9 M H R ( b ea ts /m in ) N R N R p > 0 .0 5 D in ar d i 2 0 1 3 E N D : C le ar P as sa g e® P la ce b o ( fa k e N D ) 4 8 ( 1 7 M a n d 3 1 F ) (a d o le sc en ts ) H R a ft er a ct iv it y H R % ( b ea ts /m in ) H R p er ce n ta g e in cr ea se af te r co m p le ti n g t h e ac ti v it y. E N D b ef o re = 7 7 ± 4 0 E N D a ft er = 1 5 9 ± 2 4 P la ce b o b ef o re = 6 8 ± 4 0 P la ce b o a ft er = 1 6 8 ± 2 1 p = 0 .1 2 8 p = 0 .0 1 5 A d am s 2 0 1 7 E N D : B re at h R ig h t® T u rb in e® i n te rn al N D an d W it h o u t N D 1 5 M M ea n H R ( b ea ts /m in ) st an d ar d iz ed w ar m - u p a t 3 0 , 5 0 a n d 7 0 % o f fa m il ia ri za - ti o n m ea n t im e tr ia l p o w er o u tp u t E N D 3 0 % = 9 7 ± 9 E N D 5 0 % = 1 1 4 ± 1 2 E N D 7 0 % = 1 2 7 ± 1 0 In t. 3 0 % = 1 0 0 ± 1 8 In t. 5 0 % = 1 1 7 ± 1 9 In t. 7 0 % = 1 3 0 ± 1 3 W it h o u t N D 3 0 % = 1 0 0 ± 2 2 W it h o u t N D 5 0 % = 1 1 5 ± 1 6 W it h o u t N D 7 0 % = 1 2 6 ± 8 H R 3 0 % = 0 .7 4 ; H R 5 0 % = 0 .7 5 ; H R 7 0 % = 0 .2 6 1312 European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 Ta b le 1 (c o n ti n u ed ) S tu d y In te rv en ti o n C o n tr o l N O u tc o m e d es cr ip ti o n In te rv en ti o n r es u lt s C o n tr o l re su lt s p v al u e O tt av ia n o 2 0 1 7 E N D : B re at h R ig h t® N D M as te r- ai d R o ll - fl ex ® a n d W it h o u t N D 1 3 ( 8 M a n d 5 F ) H R ( b ea ts /m in ) E N D = 1 8 1 .1 ± 1 0 M as te r- ai d R o ll -fl ex ® = 1 7 8 .7 ± 1 3 .9 W it h o u t N D = 1 7 9 .2 ± 1 2 .4 p = 0 .9 6 R P E G ri ffi n 1 9 9 7 E N D /L I an d E N D /H I P la ce b o ( st ri p w it h o u t el as ti c st ri p s in t h e ce n te r) 3 0 ( 2 0 M a n d 1 0 F ) R P E ( B o rg - 2 0 ) E N D /L I = 1 0 .9 ; E N D /H I = 1 3 .4 P la ce b o /L I = 1 1 .5 ; P la ce b o /H I = 1 4 .3 p = 0 .0 3 B ak er 1 9 9 9 E N D ( b ra n d d id n o t m en ti o n ed ) P la ce b o ( fa k e n as al d il at o r) 1 0 ( 3 M a n d 7 F ) R P E ( B o rg - 2 0 ) N o t m en ti o n ed N o t m en ti o n ed – O ’K ro y 2 0 0 0 E N D : B re at h e R ig h t® P la ce b o a n d m o u th b re at h in g ( M B ) 1 5 ( 5 M a n d 1 0 F ) R P E ( B o rg – 2 0 a n d B o rg - 1 0 ) E N D ( B o rg – 2 0 ) = 1 8 .9 ± 1 .2 2 E N D ( B o rg – 1 0 ) = 9 .1 3 ± 1 .2 P la ce b o ( B o rg – 2 0 ) = 1 8 .9 ± 1 .3 3 P la ce b o ( B o rg – 1 0 ) = 9 .3 ± 1 .2 M B ( B o rg – 2 0 ) = 1 8 .8 ± 1 .7 8 M B ( B o rg – 1 0 ) = 9 .1 ± 1 .5 8 N R T o n g 2 0 0 1 a E N D : (b ra n d d id n o t m en ti o n ed ) W it h o u t N D 8 M R P E ( B o rg – 2 0 a n d B o rg - 1 0 ) E N D ( B o rg – 2 0 ) = 1 6 .9 ± 1 .1 E N D ( B o rg – 1 0 ) = 7 .4 ± 1 .0 C o n tr o l (B o rg – 2 0 ) = 1 7 .7 ± 0 .7 C o n tr o l (B o rg – 1 0 ) = 8 .1 ± 0 .6 p < 0 .0 5 p < 0 .0 5 T o n g 2 0 0 1 b E N D : (b ra n d d id n o t m en ti o n ed ) O ro n as al b re at h in g an d P la ce b o ( fa k e N D ) 9 M R P E ( B o rg – 2 0 an d B o rg - 1 0 ) (a t ex h au st io n ) E N D ( B o rg – 2 0 ) = 1 9 .4 ± 0 .4 E N D ( B o rg – 1 0 ) = 8 .6 ± 0 .9 P la ce b o ( B o rg – 2 0 ) = 1 9 .6 ± 0 .4 P la ce b o ( B o rg – 1 0 ) = 9 .6 ± 0 .4 C o n tr o l (B o rg – 2 0 ) = 1 9 .6 ± 0 .3 C o n tr o l (B o rg – 1 0 ) = 8 .4 ± 0 .8 p > 0 .0 5 F (2 ,1 6 ) = 0 .1 2 5 p > 0 .0 5 F (2 ,1 6 ) = 3 .2 9 B o u rd in 2 0 0 2 E N D : B re at h -R ig h t® W it h o u t N D a n d n o n as al v en ti la ti o n (u si n g a n o se c li p ) 1 0 M R P E ( B o rg - 2 0 ) E N D = 1 1 .8 ± 1 .9 W it h o u t N R = 1 2 .1 ± 1 .7 N o se c li p = 1 3 .2 ± 0 .8 p = 0 .1 8 M ac fa rl an e an d F o n g 2 0 0 4 E N D : B re at h -R ig h t® P la ce b o ( fa k e N D ) an d W it h o u t N D 3 0 M ( ad o le sc en ts ) R P E ( B o rg - 1 0 ) lo n g -t er m a n ae ro b ic p o w er ( L A n P ) an d p ea k a er o b ic p er fo r- m an ce ( A eP ) N R ( S tu d y o n ly d es cr ib ed v al u es in % ) N R ( S tu d y o n ly d es cr ib ed v al u es in % ) N R N u n es 2 0 1 1 E N D : B re at h -R ig h t® P la ce b o ( fa k e N D ) an d W it h o u t N D 9 M R P E ( B o rg - 2 0 ) N R N R p > 0 .0 5 1313European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 As the study designs were similar (cross-over study), this item was not included in the table. Risk of bias assessment was also carried out indepen- dently by two researchers and any inconsistencies were resolved by a third researcher. We used the Cochrane Col- laboration risk assessment tool for randomized clinical trials, Revman software (Review Manager 5.3). This is composed of seven areas that must be evaluated: generation of random sequence, allocation concealment, blinding of participants and professionals, incomplete outcomes, report of outcome and other sources of bias [15]. The study was considered high-risk if it demonstrated a high-risk of bias in at least one of the evaluated criteria (randomization, allocation conceal- ment, blinding). Summary measures, approach to synthesis and analysis Quantitative data syntheses (meta-analysis) was performed using the random effects model of Review Manager Soft- ware 5.3 (Cochrane Community, Haymarket, London, UK) for the following outcomes: VO2max., HR and RPE. Data were pooled using a mean difference (MD) for continuous variables with a 95% confidence interval. Analysis with an I2 > 40% and a p value of chi-square test < 0.10 were consid- ered significant heterogeneity. Sensitivity analyses were performed to investigate the causes of any heterogeneity, excluding a study each time and recorded the changes in I2 and p values. Results Selection of studies Initially 624 articles were identified. After the titles and abstracts were read, duplicate studies and those that did not meet the eligibility criteria were excluded. Of these, 19 studies that matched the proposed theme of the review were selected. The flowchart for the article selection process and the results of identification, screening, eligibility and included studies is shown in Fig. 2. Study characteristics Maximal oxygen uptake (VO2max) A total of 17 studies evaluated VO2max [4–6, 10, 13, 17–19, 21–27, 29, 31], of which three indirectly assessed VO2max [5, 6, 18] in adolescents who regularly practice physical exercise. One of the studies directly assessed trained cyclists [29], others used triathletes [17, 31], and a fourth was assessed VO2max during recovery Ta b le 1 (c o n ti n u ed ) S tu d y In te rv en ti o n C o n tr o l N O u tc o m e d es cr ip ti o n In te rv en ti o n r es u lt s C o n tr o l re su lt s p v al u e A d am s 2 0 1 7 E N D : B re at h R ig h t® T u rb in e® i n te rn al N D an d W it h o u t N D 1 5 M R P E ( B o rg - 2 0 ); S ta n d ar d w ar m -u p a t 3 0 , 5 0 , 7 0 % o f fa m il - ia ri za ti o n m ea n t im e tr ia l p o w er o u tp u t E N D 3 0 % = 8 ± 1 ; E N D 5 0 % = 1 0 ± 1 ; E N D 7 0 % = 1 2 ± 1 In t. 3 0 % = 8 ± 1 In t. 5 0 % = 1 0 ± 1 In t. 7 0 % = 1 2 ± 1 W it h o u t N D 3 0 % = 8 ± 1 W it h o u t N D 5 0 % = 1 0 ± 1 W it h o u t N D 7 0 % = 1 1 ± 2 R P E 3 0 % : p = 0 .8 7 ; R P E 5 0 % : p = 0 .4 8 ; R P E 7 0 % : p = 0 .1 4 D in ar d i 2 0 1 7 E N D : C le ar P as sa g e® P la ce b o ( fa k e N D ) 3 5 M ( ad o le sc en ts ) R P E ( B o rg - 2 0 ) E N D = 7 .2 ± 1 P la ce b o = 7 .5 ± 1 .2 N R E N D e x te rn al n as al d il at o r, N D n as al d ev ic e, L I L o w -i n te n si ty , H I h ig h -i n te n si ty , N R n o t re la te d , In t. i n te rn al , M m al e, F f em al e, M in m in u te s, V O 2 m a x m ax im al o x y g en u p ta k e, H R h ea rt r at e; R P E r at in g s p er ce p tu al e ff o rt 1314 European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 from anaerobic exercise [13]. A significant difference in VO2max when using the END was noted in five studies only, whereby one evaluated male triathletes [17], three studied adolescents of both sexes who regularly practice exercise [5, 6, 18], and one study was on adult men and women (the study did not describe the training level of the volunteers) [4]. The use of a placebo END was reported in ten studies [5, 6, 13, 18, 19, 23–27] and in the others it was compared with the absence of the END [4, 10, 17, 21, 22, 29, 31]. Eight studies evaluated men and women [4, 5, 13, 22, 24, 26, 27, 31] and the others only assessed men. Other variables such as ventilation, respiratory rate, peak nasal inspiratory flow, respiratory exchange ratio, heart rate, and rating of perceived exertion were also jointly evaluated with VO2max. Heart rate (HR) Thirteen studies evaluated heart rate (HR) in men and women [4, 5, 13, 14, 17, 22–26, 28, 29, 31]. Of these, one evaluated triathlete men [17], one assessed adult male trained cyclists [29], and one investigated male and female adolescents who regularly practice physical exercise [5]. The other studies did not describe the training level of the sample. A significant difference in HR while using the END was noted in only two of the studies [4, 5]: one was carried out on male and female adults (the study did not describe the training level of the volunteers); another was on male and female adolescents who regularly practice exercise. Most of the investigations compared the END Fig. 2 The flowchart for the article selection process 1315European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 with the placebo device (seven studies) [5, 13, 23–27] and the rest concentrated on the absence of the END. Rating of perceived exertion (RPE) Certain studies classified RPE as subjective perception of respiratory exertion (SPRE). In total, ten studies [4, 6, 10, 18, 19, 24–26, 28, 29] evaluated this variable and five showed less perception of exertion with the END [4, 6, 10, 18, 19]. Only two studies evaluated adolescents who regu- larly practiced exercise: one study assessed Chinese ado- lescents [18], and another investigated Brazilian teenagers [6]. Results were similar, that is, participants using the END executed the task with less exertion. Four studies evaluated RPE in women [4, 22, 24, 26], three of which did not dem- onstrate significant changes with the use of the END [22, 24, 26]. Studies or data included on meta‑analysis Nine studies were included in the meta-analysis that evalu- ated VO2max.[5, 6, 21–23, 22, 23, 26, 31]. The VO2max. outcome was assessed in 168 participants in which no statis- tically significant difference was found, MD (95% CI) = 0.86 [− 0,43, 2.15], p = 0.19, and I2 = 0% (Fig. 3). Eight studies were included in the meta-analysis that eval- uated HR [5, 13, 14, 22, 23, 28, 29, 31]. The HR outcome was assessed in 138 participants in which no statistically sig- nificant difference was found, MD (95% CI) = 0.02 [− 3.19, 3.22], p = 0.99, and I2 = 0% (Fig. 4). Six studies were included in the meta-analysis that evalu- ated RPE [6, 10, 19, 26, 28, 29]. The RPE outcome was assessed in 92 participants in which no statistically signifi- cant difference was found, MD (95% CI) = − 0.12 [− 0.52, 0.28], p = 0.56, and I2 = 27% (Fig. 4). In the sensitivity analysis, excluding one study at a time did not change the direction and significance of the outcomes. Effects of END on maximal oxygen uptake (VO2max) Two experimental situations (with and without END) were tested in the study by Griffin et al. [4]. A decrease in VO2 was observed in healthy adults after a low exercise protocol and high intensity. Dinardi et al. [5] observed a significant difference in VO2max. in adolescents who used the END and placebo. Macfarlane and Fong [18] also studied adolescents with END. An improvement of 3.2% was reported and 2.9% in aerobic performance compared to the control condition and placebo, respectively. Using a maximum characteristic test, Dinardi et al. [6] observed a significant difference in VO2max. in healthy adolescents who played soccer regu- larly. Tong et al. [10] did not observe significant changes in VO2 in men submitted to 30 series of 20 s each, when compared with and without the END. Thomas et al. [13] did not observe significant changes in VO2 in 14 individuals (8 men and 6 women) regarding the effectiveness of END in recovery after anaerobic exercise. In the study of Nespereira et al. [17], the use of END resulted in a small but significant reduction in VO2 in three different intensities, compared to the non-use of END in male triathletes. Using a protocol of Fig. 3 VO2max (END vs control). END external nasal dilator, IV inverse variance, CI confidence interval, SD standart deviation 1316 European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 moderate intensity in nine men, Tong et al. [19] observed no difference in VO2 between the conditions tested. Trocchio et al. [21] observed no significant difference in VO2max. when adult athletes used the END compared to not using it. Chinevere et al. [22] evaluated ten adults (four men and six women) in a maximum treadmill test in five experimen- tal conditions. When using the END, there was no differ- ence between the conditions. Case et al. [23] evaluated the performance of nine men at running intervals and observed that there was no difference in VO2max. Baker et al. [24] also they did not observe improvement in the aerobic per- formance in ten adults (seven women and three men) when they used the END, compared to the placebo. In the study conducted by Nunes et al. [25], there was no performance improvement (VO2) in nine adults who used the END evalu- ated on an ergometer cycle, compared to placebo and not using the device. Data from O’kroy’s [26] study demonstrate no significant difference on VO2max. measurements with the END compared to the placebo test and in the oral condition (nose clip) in 15 healthy adults (10 women and 5 men). Sub- sequently O’kroy et al. [27] also did not observe significant difference when the individuals used the END, compared to the placebo. Adams et al. [29] observed no significant differ- ence in the average movement economy using the END com- pared to an internal device and without the END. Ottaviano et al. [31] used three experimental situations (with nasal dilator Breath Right®, nasal dilator Master-aid Roll-flex® and without nasal device) to evaluate 13 adult triathletes (8 Fig. 4 HR and RPE (END vs control). END external nasal dilator, IV inverse variance, CI confidence interval, SD standart deviation, HR heart rate, RPE rating of perceived exertion 1317European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 men and 5 women) regarding the effectiveness of the END. Considering the VO2max. between the three situations, no significant difference was observed. When individuals breathed only through their nose, VO2max. nasal proved to be significantly higher when dilators were used. Effects of END on heart rate (HR) Griffin et al. [4] observed a reduction in HR in healthy adults after a low exercise protocol and high intensity. Dinardi et al. [5] observed in adolescents athletes who used END com- pared to placebo, a drop in HR after the cardiorespiratory test. Thomas et al. [13] did not observe significant changes in HR in 14 individuals (8 men and 6 women) regarding the effectiveness of END in recovery after anaerobic exercise. Overend et al. [14] evaluated HR in 19 healthy adults using mouthguards during two experimental situations (END and without END) in a treadmill exercise protocol. There was no positive effect of END on HR at the following levels of the test used: (1) transition between walking and running, (2) time when the participant wished to remove the mouthguard, (3) moment of fatigue. In the study by Nespereira et al. [17] the use of END did not result in significant differences in HR when using END compared to not using it in three dif- ferent intensities in the protocol used. Chinevere et al. [22] evaluated ten adults (four men and six women) in a maxi- mum treadmill test in five experimental conditions (nose, nose + END, mouth, mouth + nose, mouth + nose + END). Maximum heart rate was significantly lower only in the “nose” condition, compared to the other conditions. Case et al. [23] evaluated the performance of nine men at run- ning intervals and observed that there was no difference in HR between the conditions analyzed. Baker et al. [24] found no improvement in the aerobic performance in ten adults (seven women and three men) when they used the END, compared to the placebo. In the study conducted by Nunes et al. [25], HR was not affected in nine adults who used the END evaluated on an ergometer cycle, compared to placebo and not using the device. Data from the O’kroy’s [26] study demonstrate that HR did not show a significant difference in the END test compared to placebo and mouth condition (nose clip) in 15 healthy adults (10 women and 5 men). Bourdin et al. [28] did not observe differences in ten male triathletes after comparing the END with no nasal ven- tilation (close clip) and without the END. Adams et al. [29] observed no significant difference in the mean HR using the END compared to an internal device and without the END. Ottaviano et al. [31] used three experimental situations (with external nasal dilator Breath Right®, nasal dilator Master- aid Roll-flex® e without nasal device) to evaluate 13 adult triathletes (8 men and 5 women) regarding the effectiveness of the END. Considering the HR between the three situa- tions, no significant difference was observed. Effects of END on rating of perceived exertion (RPE) Griffin et al. [4] observed a reduction in RPE in healthy adults after a low exercise protocol and high intensity. Baker et al. [24] and Nunes et al. [25] showed no significant dif- ference when the participants used the END compared to the placebo. Both studies did not present the data from the RPE. Data from the O’kroy’s [26] study demonstrate that RPE did not show a significant difference in the END test compared to placebo and mouth condition (nose clip) in 15 healthy adults (10 women and 5 men). On the other hand, Tong et al. [10] observed a significant difference in RPE when eight men used the END compared to the absence of the device. Bourdin et al. [28] did not observe differences in ten male triathletes after comparing the END with no nasal ventilation (close clip) and without the END. Dinardi et al. [6] observed a significant difference in RPE in adoles- cents who used the END and placebo. Macfarlane and Fong [18] also evaluated adolescents with END. The breathing effort perceived by the subjects was significantly lower in the ENDs condition compared to the control after both the long-term anaerobic power (LAnP) and peak aerobic per- formance (AeP) tests, while the placebo had no significant impact on the subjects RPE during these two tests. Using a protocol of moderate intensity in nine men, Tong et al. [19] observed no difference in RPE (Borg-20 and Borg-10) (at exhaustion) between the conditions tested. Adams et al. [29] observed no significant difference in the RPE using the END compared to an internal device and without the END. Risk of bias in included studies Reliability for evaluators measuring bias risk was verified by the kappa statistic (0.81). Of the 19 RCT studies included in this systematic review and meta-analysis, the bias risk assessment revealed that most studies (18 studies) demon- strated a high risk of bias or uncertain risk (Fig. 5). Only one study had a low risk of bias [6]. Discussion To the best of our knowledge, this is the first systematic review of the literature and meta-analysis that has evaluated the effects of the external nasal dilator on performance in physical exercise. Of the 19 studies included in this review, 8 demonstrated an improvement in one or more of the per- formance parameters during physical exercise for healthy adolescents or adults of both sexes using the external nasal dilator [4–6, 10, 14, 17–19]. In one of these studies, where a positive impact was noted for END usage in physical exer- cise, the sample was comprised of healthy male adolescents and those with allergic rhinitis [6]. 1318 European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 Despite these findings, through studies included in the meta-analysis, the external nasal dilator showed no improve- ment on VO2max, HR and RPE results in healthy individuals during exercise. Numerous studies have shown that the END increases the cross-sectional area of the nasal valve, reduces nasal resist- ance, transnasal inspiratory pressure, stabilizing the lateral nasal vestibule, and preventing its collapse during final inha- lation [4, 6–8, 20]. Specifically in relation to performance during physical exercise, several investigations provide con- tradictory results. In a study by Seto-Poon et al., it was noted that after progressive stages of exercise lasting 1 min on a cycle ergometer at a rate of 60 rpm, there was a delay in the start of the switching point from nasal to oronasal breath- ing in healthy adults (four men and five women), that is, the END prolonged the duration of nasal breathing during exercise and lessened inspiratory nasal resistance at rest in seven volunteers (p < 0.01), assessed with rhinomanometry [9]. In view of this evidence that the END delays the onset of oral breathing during exercise, favoring output and nasal function, several studies have been conducted with the aim of verifying its effectiveness in physical exercise. Tong et al. evaluated the effect of the END on nine trained men when practicing aerobic exercise of moderate intensity (75% of VO2max), randomized in oronasal, nasal breathing with the END and placebo condition [10]. It was concluded that nos- tril dilation when using the END resulted in an increase in nasal ventilation capacity, in physical exercise maintained at 75% of VO2max and reduced the perceived magnitude of respiratory exertion during exercise [10]. In a study by Griffin et al., there was a reduction in VO2max noted in 30 healthy athletes evaluated at 2 intensi- ties on the cycle ergometer (100 W and 150 W) when utiliz- ing the END [4]. Participants were randomized using a dou- ble-blind, controlled design and a control group. Studying a pediatric population, Macfarlane and Fong randomized 30 healthy male Chinese students, with mean age of 15.2 years, in 6 equal groups, analyzing 3 conditions: END, placebo and control [18]. There was no significant difference in experi- mental situations with anaerobic characteristics. However, regarding aerobic performance, the END demonstrated a sig- nificant increase of 3.2% (p = 0.037) and 2.9% (p = 0.018) compared to the control condition and placebo, respectively. In addition, there was an improvement in the subjective sensation of exertion compared to the placebo (p = 0.048) and the control (p = 0.016). Notwithstanding the methodo- logical differences, studies such as Thomas et al., Trocchio et al., Chinevere et al., Case et al., Baker et al., Nunes et al., O’Kroy, O’Kroy et al., Bourdin et al., Adams et al. did not demonstrate differences between the experimental and pla- cebo conditions during physical exercise when using the END on healthy individuals [13, 21–29]. It is worth highlighting that most investigations evaluated the effects of the END in tests with aerobic characteristics. The use of the END in high-level sports has become com- mon due to its absence from the World Anti-Doping Agency (WADA) list, since the expected and proven effects are not prohibited [30]. Along these lines, Bourdin et al. evaluated ten randomized male triathletes in three experimental con- ditions: normal nasal ventilation, no nasal ventilation (nose clip used) and END usage [28]. The study revealed that changes in nasal ventilation when using the END did not have an impact on heart rate or the rate of perceived exer- tion of the triathletes, when running five minutes at 80% of the maximum aerobic condition. Recently, Dinardi et al. evaluated 65 adolescents who regularly played football [6]. Of these, 35 were healthy and 30 had allergic rhinitis. It was noted that use of the END significantly increased nasal patency and aerobic capacity both in healthy adolescent athletes and those with allergic rhinitis. Moreover, a sig- nificant reduction in nasal resistance was noted, assessed by rhinomanometry [6]. In a previous study, this same group of researchers noted that in a track race test, adolescent ath- letes using the END, as opposed to the placebo, showed Fig. 5 Risk of bias graph: review authors’ judgements about each risk of bias item presented as percentages across all included studies 1319European Archives of Oto-Rhino-Laryngology (2021) 278:1307–1320 1 3 an improvement in VO2max (53.0 ± 4.2 mL/kg−1/min−1 and 51.2 ± 5.5 mL/kg−1/min−1, respectively) (p < 0.05), a drop in heart rate after the cardio-respiratory test (END = 159 beats/ min and placebo = 168 beats/min) (p = 0.015); improvement in nasal patency measured by the peak nasal inspiratory flow (PNIF) (123 ± 38L/min and 117 ± 35L/min, respectively) and reduction of dyspnea evaluated by the visual analog scale (VAS) (p < 0.05) [5]. With the hypothesis that the END would facilitate the distribution of oxygen to the body and prevent fatigue of the respiratory muscles, O’Kroy et al. applied two maxi- mum tests on a cycle ergometer to 14 healthy untrained adults with the aim of proving this theory [27]. Parameters such as VO2max, ventilation, tidal volume, respiratory rate, among others, were assessed and there was no difference noted between the experimental and placebo conditions, during exercise. In a previous study, O’Kroy evaluated ten healthy women and five healthy men under the parameters of VO2max, maximum ventilation and maximum work rate (rating of perceived exertion and dyspnea) [26]. The volun- teers completed the three tests on a cycle ergometer until fatigue set in, in a random manner for three experimental situations (control, END and placebo). This investigation concluded that the END did not improve performance, as evaluated through direct measurements of aerobic capac- ity. Furthermore, the subject measurements of exertion and dyspnea did not have an impact on physical exercise with the use of the END. A study conducted by Tong et al. assessed the work of the ventilatory muscles in eight healthy, untrained adults during intermittent exercise [19]. The train- ing workload proposed corresponded to 30 series of 20 s each and a 40 s interval at the end of each series on the cycle ergometer. In seven of the eight individuals, a greater aver- age initial power was noted in the tests where the END was used, compared to the control (p < 0.05) and lower subjec- tive perception of exertion and breathing (p < 0.05). There was no impact on the ventilatory responses and VO2max in both experimental situations. The use of the END may have resulted in an absence of fatigue in the ventilatory muscles, leading to an increase in initial power for the exercise and a reduction in the perceived magnitude of respiratory exertion. Recently, Ottaviano et al. evaluated 13 healthy triathletes (8 men and 5 women) in 3 experimental situations (2 differ- ent brands of END and without the END) [31]. A progres- sive treadmill test was applied, where volunteers were told to breathe predominantly through the nose. There was no significant difference in the VO2max variable, evaluated by direct method, in the three experimental conditions. On the other hand, in the nasal VO2max and in the nasal breathing time, there was a significant improvement when the nasal dilators were used (p < 0.001 and p = 0.015, respectively). Using a randomized crossover design, Adams et al., sub- mitted 15 trained cyclists to a 20 km test, in 3 experimental situations (Breathe Right® external nasal dilator, Turbine® internal nasal dilator and no dilator) [29]. The use of nasal dilators, regardless of the mechanism (internal or external), did not have an impact on the performance of the healthy trained cyclists. The authors suggest that the effectiveness of these devices in a competitive sporting environment should be questioned. Limitations The inherent limitations in this systematic review and meta- analysis are the low number of studies and the lower quality of published studies evaluating nasal dilators in the physi- cal exercise. The majority of the included studies presented high risk of bias and small samples, with no placebo, mostly healthy individuals and a wide variety of tests utilized. More high quality studies should be conducted to provide robust evidence and to clarify the effects of external nasal dilator during physical exercise in healthy persons. Conclusion Although the external nasal dilator is a low-cost, low-risk device, free from any regulatory restrictions by the World Anti-Doping Agency (WADA), this systematic review and meta-analysis found no improvement in VO2max, HR and RPE results in healthy individuals during exercise. Author contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by RRD, CHSF, GSS, VEAS, CCI and CRA. The first draft of the manuscript was written by RRD and CHSF and all authors com- mented on previous versions of the manuscript. All authors read and approved the final manuscript. Funding None. Compliance with ethical standards Conflict of interest The author(s) declare that they have no conflicts of interest to declare. Ethical approval This article does not contain any studies with human participants or animals performed by any of the authors. References 1. Nigro CE, Nigro JF, Mion O, Mello JF Jr (2009) Nasal valve: anatomy and physiology. Braz J Otorhinolaryngol 75(2):305–310 2. Kiyohara N, Badger C, Tjoa T, Wong B (2016) A comparison of over-the-counter mechanical nasal dilators: a systematic review. 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A systematic review and meta-analysis Abstract Background Objectives Methods Results Conclusions Introduction Materials and method Eligibility criteria Databases and search strategy Selection of studies Data extraction and risk of bias assessment Summary measures, approach to synthesis and analysis Results Selection of studies Study characteristics Maximal oxygen uptake (VO2max) Heart rate (HR) Rating of perceived exertion (RPE) Studies or data included on meta-analysis Effects of END on maximal oxygen uptake (VO2max) Effects of END on heart rate (HR) Effects of END on rating of perceived exertion (RPE) Risk of bias in included studies Discussion Limitations Conclusion References