INTRODUCTION The practice of yoga in recent years is becoming more common. Originating in India, yoga combines physical postures with a philosophy of life and breathing (pranayama). One of the breaths used during yoga practice is the so-called ujjayi or victorious breath. It consists of the voluntary contraction of the muscles of the larynx both in inspiration and expiration. This reduces the diameter of the larynx, reducing airflow and thus increasing intrathoracic pressure, as well as increasing expiratory/inspiratory time and reducing respiratory rate and dead space. It also increases oxygen saturation in healthy subjects, increasing respiratory effort. Several studies have verified the relationship between ujjayi breathing and increased BRS (cardiovagal baroreflex sensitivity), by stimulation of the parasympathetic system at the glottis level.

This would favor a decrease in heart rate, as well as better control of stress and anxiety.

The cardiovascular and respiratory effects studied with ujjayi breathing have not evaluated the effect that this breath has on the activation of the respiratory muscles, mainly the diaphragm. The diaphragm is the main inspiratory muscle and as such, lung volumes and intrathoracic pressures created during respiration depend on its activation and position.

In recent years, ultrasound has become a technique widely used by pulmonologists and intensivists. It is an easy technique to perform, reproducible, non-ionizing, allows bilateral comparison, non-invasive and non-painful and whose results can broaden the information from other techniques such as spirometry and radiography.

There are standardized protocols to measure the diaphragmatic excursion, the thickness of the diaphragm HYPOTHESIS: ujjayi breathing is capable of generating greater activation of the diaphragm in subjects healthy with respect to spontaneous or pursed-lip breathing.

OBJECTIF: study and compare the activation and work of the diaphragm in different type of breathing (ujjayi, pursed lips and at rest) in healthy subjects who practice yoga or not. DESIGN: cross over study experimental, analytical and prospective. METHODOLOGY: 80 healthy subjets (40 yoga practitioners and 40 non yoga practitioners) participated at this study. All of them volunteers will undergo an ultrasound study of their diaphragm. To do this, following the stipulated protocol, three variables will be analyzed: diaphragm thickness, its rate of contraction, and diaphragmatic excursion, all of them at rest, ujjayi breathing, and pursed-lip breathing.

The ultrasound measurements will be taken by a single researcher, who is not the main one, and who will not know which group each of the subjects belongs to, thus avoiding an evaluation bias. To avoid bias and according to the RUSI regulations, the researcher will take 3 measurements of each of the explorations with the average of the 3.

Inclusion Criteria:

• yoga practitioners for more than a year

Exclusion Criteria:

• respiratory pathology
• thoracic deformities
• neuromuscular diseases
• Under treatment with corticosteroids, muscle relaxants and/or barbiturates
• allergic episodes in the last 3 weeks
• thoracic or abdominal surgeries in the last 3 weeks

All the researchers will participate in all the study phases