Table 3. Procedures and main findings of the included studies investigating the effects of NB and OB on respiratory muscles.

First author (year)	Performed analyses	Main findings
Trevisan et al.6 (2015)	sEMG signals were acquired using a 14-bit surface electromyograph to evaluate the electrical activity of the SCM, UT, sternocleidomastoid, upper trapezius, and amplitude of diaphragm movement during NB and OB. Muscle activity was recorded at rest for 10 s and in four inspiratory tests: Sniff, TLC, PNIF, and MIP.	The EMG activities of the SCM and UT did not differ between the OB and NB groups at rest and at TLC, except for the left UT, which exhibited significantly higher activity at TLC in the OB group. The mean MIP value was significantly lower in the OB group than in the NB group. Among the Sniff, PNIF, and MIP, SCM activity was lower in the OB group.
Ribeiro et al.26 (2004)	EMG recording analysis to evaluate SCM and UT muscle activity in children during NB and OB, during relaxation and maximal voluntary contractions.	At rest, children had higher electrical activity during OB than during NB (P < 0.05). In the maximal voluntary contraction, there was lower activity during OB compared with NB (P < 0.05).
Tafil-Klawe and Klawe27 (2003)	EMG recording of the GG muscle activity during NB and OB to determine the influence of NB on GG in progressive hypoxia.	Compared with NB, there are smaller increases in GG-EMG-activity in response to hypoxia during OB. Participants aged >40 years showed reduced GG muscle response to hypoxia, which was most pronounced during OB.
Takahashi et al.28 (2002)	EMG recording of the GG and GH muscles to evaluate the influence of NB and OB can influence their activity. Activities were recorded simultaneously over 20 respiratory cycles during NB and repeated during OB.	A substantial difference was observed during NB in the upright position, with greater activity in the GG muscle. The GH muscle showed greater EMG activity during maximal jaw opening.

NB: nasal breathing, OB: oral breathing, sEMG: surface electromyography, SCM: strenocleidomastoideus, UT: upper trapezius, TLC: total lung capacity, PNIF: peak nasal inspiratory flow, MIP: maximal inspiratory pressure, GG: genioglossus muscle, GH: geniohyoid