The aerobic exercise will be developed in interval mode, on a treadmill with a negative slope of up to -6% for the intervention group, performing a 2-minute interval with the workload estimated in METS, followed by another 4-minute interval with half the work intensity. It will last between 20 and 30 minutes. The intensity or workload will be individualized (between low and medium), according to the functional status of each participant and will be gradually increased depending on their tolerance. The working heart rate will be between 60% and 80% of the theoretical maximum HR, the oxygen saturation. It should never go below 90% and the subjective perception of effort according to the modified Borg scale will have its objective between 4 and 6 maximum. The treadmill used is the Commercial X22i model from Nordictrack, with a maximum slope of -6º.

The aerobic exercise will be carried out in interval mode, on a treadmill with a positive slope, performing a 2-minute interval with the workload estimated in METS, followed by another 4-minute interval with half the work intensity. It will last between 20 and 30 minutes. The intensity or workload will be individualized (between low and medium), according to the functional status of each participant and will be gradually increased depending on their tolerance. The working heart rate will be between 60% and 80% of the theoretical maximum HR, the oxygen saturation It should never go below 90% and the subjective perception of effort according to the modified Borg scale will have its objective between 4 and 6 maximum. The treadmill used is the Commercial X22i model from Nordictrack, with a maximum slope of 40º

An effort retraining program will be carried out, with respiratory physiotherapy, muscle strengthening exercises and aerobic exercise, for four weeks, every other day, with a duration of 75 minutes each session. Both the control and experimental groups will receive a common treatment: Muscle strength and aerobic resistance exercises will be performed following the F.I.T.T principle, working the main muscle groups against resistance (between 40% and 60% RM) performing three sets of ten repetitions of each one. It will begin with a warm-up and then a cool down with stretching. We will apply respiratory physiotherapy techniques to promote ventilation and drainage of secretions.

Next, the aerobic work is carried out according to the assigned group: treadmill with a positive slope (experimental group), treadmill with a negative slope (control 1) or cycle ergometer (group 2).

The dominant quadriceps (defined by the leg that is usually used to climb stairs or kick a ball) is measured, with the patient's starting position being supine with the knee completely extended and relaxed. While previous studies suggested a minimum of 30 minutes of rest before performing the ultrasound, more recent studies indicate that 5 minutes after adopting the supine position, measurements normalize. There is no consensus on the measurement point, but it is proposed to place the probe at the midpoint of the muscle length (50% rule), taking the greater trochanter and proximal edge of the patella as reference. It is also advisable to place the probe midway between the medial and lateral edges of the muscle. Once the placement point of the probe has been determined, it is placed as perpendicular as possible to the skin using a generous amount of transducer gel and exerting the minimum possible pressure to avoid compression of the dermal surface and muscle distortion.

A convex probe of 2.5 to 3.5 MHz is used. In obese subjects, to have better visibility, the frequency chosen is 1.5 MHz.

The subjects are in a supine position, with the head of the stretcher flat and their legs bent at 30-45º. The probe is positioned firmly below the right costal arch and on the line drawn corresponding to the middle of the clavicle, orienting it cranially. At that point, the dome of the right hemidiaphragm is visualized, appearing as a thick hyperechoic line. The highest diaphragmatic position is sought, which is the part of the diaphragm that produces the most craniocaudal excursion, and the transducer is kept firmly in position during the phases of the respiratory cycle and measurements of tidal volume breathing. The M mode modality is then activated, which provides us with the diaphragmatic movement pattern, placing the M beam line around 30º in the posterior part of the cranio-caudal midline: cranio-caudal diaphragmatic excursions.

The measurement of the thickness of the diaphragm is taken in the right hemidiaphragm since it is more accessible than the left through its hepatic window. To evaluate the thickness, a linear probe at 10-12MHz is used, placing it perpendicular to the intercostal space between the 9th and 10th rib, in the anterior part of the axillary line. At this level, 3 parallel layers with different echogenicity are observed corresponding to the pleura, the diaphragm and the peritoneum. The measurement is carried out with M mode, where the image is frozen in an unforced expiration (representing the functional residual capacity) and in a maximum inspiration. The distance between the inner edge of the pleural line and the inner edge of the peritoneal line is measured. The measurement is carried out three times and the average of the three is taken.