The Impact of Diaphragmatic Breathing Instructions and Inspiratory Pressures on Diaphragm Contraction in Healthy Adults

Diaphragmatic and Sternocleidomastoid Muscle Recruitment at Various Inspiratory Loads With and Without Breathing Instruction in Healthy Adults

This is a cross-sectional obsessional study.

This study aims (1) to investigate the relationship between sternocleidomastoid muscle recruitment and diaphragm thickness fraction during increasing inspiratory resistance in healthy adults; (2) to compare diaphragmatic and sternocleidomastoid muscle recruitment patterns with and without a standard diaphragmatic breathing instruction with increasing inspiratory resistance in healthy adults.

Participants will be asked to breathe through a pressure threshold inspiratory loading device under different inspiratory resistances with and without a standard diaphragmatic breathing instruction. sternocleidomastoid muscle activity will be measured with surface electromyography, and diaphragm thickness will be assessed with ultrasonography.

Upon arrival at the laboratory, eligible participants will first perform a standard spirometry lung function test. The maximum inspiratory pressure (MIP) will be determined with a pressure threshold inspiratory loading device (POWERbreathe, K2). Each participant will then be instructed to use the device to perform, in random order, 10 breaths at an inspiratory intensity of 30%, 40%, 50%, 60%, 70%, and 80% MIP. A rest period of 15 minutes will be allowed between each inspiratory pressure set of 10 breaths. Simultaneous surface electromyographic (sEMG) recording of the right sternocleidomastoid muscle and ultrasound of right diaphragmatic thickness will be conducted during each breath.

The entire recording procedure will be repeated on a separate day. During the repeat measurements, participants will be provided with specific breathing instruction to focus on the use of the diaphragm and to inhale air to the lower part of the chest. Practice trials will be conducted to ensure participant's understanding of diaphragmatic breathing.

Inclusion Criteria:

• Participants ≥18 years of age with normal health

Exclusion Criteria:

• Pregnancy.
• Participants with known cardiovascular, pulmonary, musculoskeletal or psychiatric disorders.
• Participants with respiratory symptoms (from flu or other respiratory infection during the 2 weeks prior to measurements.
• Participants can not cooperate the maximal inspiratory pressure measurement.