Outcomes
’s lumbar spine, thoracolumbar, fatigue, pain
CREST, CONTRACTION, CONTRACTIONS
The intervention lasted for four weeks. All variables were measured pre- and post-test. For all of the variables, whenever possible, the minimal clinically important difference (MCID) to be detected was established. The study’s main variable was pain intensity measured with a VAS scale of 0–10 cm [The PBU was inserted under the subject’s lumbar spine, between the ribcage and the sacrum, in the area corresponding to the thoracolumbar fascia. It was inflated to an initial pressure of 40 mmHg. The patient was supine on a stretcher, with the knees flexed at 90º and a pillow under the neck to maintain a comfortable and neutral posture (Fig. 
Pressure biofeedback unitBefore the test, all the participants were instructed to perform the abdominal contraction maneuver to focus the action on the transverse abdominis, not the rectus or obliques abdominis. Several contraction trials were allowed before the recording was taken until the performance was judged optimal by the physiotherapist. A prudential rest time of 2 min was allowed so that fatigue did not intervene in the assessment result, with the minimum being 30–60 s [The drawing-in abdominal contraction maneuver was requested to record the test result, and the peak pressure change was taken into account with a record of 10 s of contraction. The result was calculated by identifying the peak point of contraction held for more than 1 s and then subtracted from the baseline pressure. Three trials were used for statistical analyses, taking the average of the three contractions.The bioPlux surface electromyograph was used with its corresponding software and TIGA-MED gold bipolar surface electrodes.Before placing the electrodes, the detection surfaces were adequately cleaned and shaved when necessary, following the recommendations of the ISEK (International Society of Electrophysiology and Kinesiology) and SENIAM (Surface Electromyography for Non-Invasive Evaluation of Muscles) to allow a low impedance between the skin and the electrodes [First, the reference electrode or ground electrode was placed on the ankle, above the right external malleolus, since it is one of the places with the least electrical activity in the body. This electrode was connected to the G channel of the bioPlux device and waited for 30 s. The reference electrode collects the basal electrical signal, which is always present on the skin surface and is not the result of muscle activity. Next, the two electrodes of channel 1 were placed on the area corresponding to the TrA/OI (obliquus internus abdominis) muscles, located 2 cm from the anterior superior iliac spine and with a distance of 2 cm between their centers [The center and edges of the electrode detection zones were pressed firmly to ensure good contact with the patient’s skin. Initially, the patient’s basal tone was measured for 30 s. Once the result was recorded, the maximal voluntary isometric contraction of the TrA was requested following the SENIAM standards to obtain the maximum force peak. Three contractions of 5 s each with 3 s of rest between repetitions were requested. Two more repetitions of the entire sequence were performed with a 60-second rest between each sequence. By recording a very low-intensity signal mixed with other undesirable ones, the signal was amplified x1000, and the bandpass was filtered from 20 to 450 Hz, quantifying it afterwards. All these results were recorded, and the bioPlux device calculated the average, giving the mV (millivolts) values of the force test as a result.Finally, 10 s of maximum contraction of the TrA were requested to assess muscle resistance. This contraction was also recorded due to the resistance test with mV.For the measurement of TrA, we used the bioPLUX wireless System Surface US. The patient was placed in a quadruped position. The conductive gel was applied to a transducer at 7.5 MHz. This was placed transversely on the right side of the body, with the center positioned at a point 2.5 cm anterior to the axillary midline, at the midpoint between the last rib and the iliac crest. Once a clear image of the TrA was obtained, it was measured at rest, freezing the image at the end of the patient’s exhalation and measuring the width at its widest point. The patient was then asked to perform an abdominal maximal voluntary isometric contraction, and the image was re-frozen at the end of the patient’s expiration for measurement. A total of three images of the contracting TrA were captured, and muscle thickness measurements in millimeters were averaged.