The EG (experimental group) will perform the diaphragmatic fatigue protocol using a specific inspiratory endurance test, in which volunteers, one-on-one, and in a single session, will breathe against submaximal inspiratory loads equivalent to 60% of their MIP (Maximum Inspiratory Pressure) through a threshold valve device. The participants will follow a free pattern of breathing until they are unable to establish flow during at least 3 maximum inspiratory efforts.

they will not receive any intervention. Just sit and wait the same amount of time that the intervention and the activation group needs to finish their protocol (around 10 minutes)

The activation group will perform the protocol of 2 sets of 30 repetitions at 40% of their MIP, one-on-one, and in a single session, breathing against submaximal inspiratory loads using a threshold valve device. The participants will follow a free pattern of breathing until complete the protocol.

The subjects will perform deep inspirations against a threshold device with varying resistances,

It will be assessed using a MicroRPM® (MicroMedical, UK).The MicroRPM® is likely a respiratory pressure meter or manometer designed for measuring respiratory muscle strength. It typically includes a mouthpiece connected to a pressure sensor, and the device measures the force or pressure generated during respiratory maneuvers.

The person will be instructed to take a maximal deep breath in, and then exhale to residual volume. After that, they will be asked to inhale forcefully against the resistance provided by the MicroRPM®. This measures the strength of the inspiratory muscles.

The measures will be expressed in cmH2O.

Diaphragmatic thickness and thickening fraction The linear array probe with a frequency of 3.0-10 megahertz (MHz) is placed perpendicularly to chest wall close to the mid-axillary line which is between the 8th and 10th intercostal space. The thickness of diaphragm is measured at the end of expiration and maximum inspiration for three times and the average values were recorded.

The measures will be expressed in centimeters.

The convex array probe with a frequency of 1.5-4.6 MHz is placed below the midclavicular line of the right costal margin in longitudinal scanning plane. The liver was used as an inspection window, and the probe was pointed toward the cephalic side. The ultrasound bundle is perpendicular to the posterior third of the right diaphragm. M-mode ultrasound is used to record the diaphragmatic movement curve during quiet breathing (QB) and deep breathing (DB).

The measures will be expressed in seconds.

The analysis of Heart Rate Variability will be conducted using a heart rate monitor. Cardiac electrical signals will be monitored with a band placed on the chest for 5 minutes with the subject in supine position on a stretcher, in a quiet environment, soft light, and a comfortable temperature. Subjects are instructed not to speak or make voluntary movements during this analysis.