The Main Role of Diaphragm Muscle as a Mechanism of Hypopressive Abdominal Gymnastics to Improve Non-Specific Chronic Low Back Pain: A Randomized Controlled Trial

Background: Chronic low back pain (LBP) has been stated as one of the main health concerns in the XXI century due to its high incidence. Objective: The objective of this study was to determine the effects of an 8-week program of hypopressive abdominal gymnastics (HAG) on inspiratory muscle strength, diaphragm thickness, disability and pain in patients suffering from non-specific chronic LBP. Methods: A total of 40 patients with chronic LBP were randomly divided into two groups. The experimental group carried out an 8-week supervised program of HAG (two sessions/week), whereas the control group did not receive any treatment. Outcomes were measured before and after the intervention, comprising diaphragm thickness during relaxed respiratory activity, maximal inspiratory pressure (PI(max)), pain intensity (NRS), pressure pain threshold and responses to four questionnaires: Physical Activity Questionnaire (PAQ), Roland–Morris Disability Questionnaire (RMQ), Central Sensitization Inventory (CSI) and Tampa Scale of Kinesiophobia-11 Items (TSK-11). Results: Statistically significant differences (p < 0.05) were observed for greater thickness of the left and right hemi-diaphragms at inspiration, as well as higher PI(max) and decreased NRS, CSI and RMQ scores in the intervention group. After treatment, the increases in the thickness of the left and right hemi-diaphragms at inspiration and PI(max), as well as the decrease in the NRS and RMQ scores, were only predicted by the proposed intervention (R(2) = 0.118–0.552). Conclusions: An 8-week HAG intervention seemed to show beneficial effects and predicted an increase in diaphragm thickness and strength during inspiration, as well as a reduction in pain intensity, central sensitization and disability, in patients suffering from chronic non-specific LBP with respect to non-intervention.