This study aims to compare the effects of abdominal air pressure resistance training, abdominal weight training, and breathing exercises on diaphragmatic strength, endurance, and physiological responses in young healthy adults.
Forty-two healthy adults aged 18-35 years will be randomly allocated to one of three groups: abdominal air pressure resistance training, abdominal weight training, or breathing exercises. Participants will complete supervised training sessions three times per week for eight weeks, with standardized breathing cadence, training volume, and therapist contact time across groups.
This trial will provide the first direct comparison of a programmable pneumatic abdominal loading method with traditional abdominal weight loading and standard breathing exercises in healthy young adults. The findings will help determine the relative effectiveness, tolerability, and safety of these interventions for enhancing diaphragmatic function. The results may contribute to the development of evidence-based respiratory muscle training strategies for rehabilitation, health promotion, and performance enhancement.
males and females with a body mass index (BMI) between 18.5 and 29.9 kg/m²
non-smokers
have not participated in structured respiratory muscle training within the previous six months
able to understand the study procedures
have a known cardiopulmonary, neuromuscular, or significant metabolic disease
experience a respiratory infection or respiratory symptoms within the preceding 2-3 weeks
pregnant
have undergone major abdominal or thoracic surgery within the previous six months
Parallel
Abdominal Air Pressure Resistance Training
Other interventionIn the AAPR group, resisted diaphragmatic breathing will be performed using a pneumatic abdominal garment or cuff capable of delivering quantifiable air pressure. The abdominal binder was securely fitted around the participant's waist, while the manual sphygmomanometer cuff was positioned vertically over the epigastric region within the abdominal binder. The cuff was inflated to provide external resistance during diaphragmatic breathing. Care was taken to ensure that the cuff and binder did not exert excessive compression over the lower thoracic region or diaphragm, thereby avoiding mechanical restriction of diaphragmatic excursion and allowing participants to maintain their normal, unrestricted diaphragmatic breathing pattern throughout the intervention. Training will begin at a pressure eliciting moderate perceived breathing effort (Borg RPE) or within a predefined range of 5-10 cmH₂O. Pressure will be increased based on Borg exertion level of 5-7.
Abdominal Weight Training (AWT)
Other interventionIn the AWT group, diaphragmatic breathing will be performed with an external load applied to the anterior abdominal wall using a standardized sandbag or weight pack, with participants positioned in supine crook-lying. Load prescription will be implemented using a pre-specified method, which included either a fixed initial load of 2-5 kg with weekly increments of 0.5-1 kg as tolerated, an initial load corresponding to 3-5% of body mass with weekly progression, or load titration based on perceived exertion targeting a Borg RPE of 4-5 during training sets. Training volume, set duration, and rest intervals will be matched to those of the AAPR group. For each session, the load applied, perceived exertion, and symptom responses will be documented.
Breathing Exercise Control (BE)
Other interventionIn the BE control group, standardized diaphragmatic breathing combined with paced slow deep breathing will be performed without the application of external resistance. Training duration, breathing cadence, number of sets, and rest intervals will be matched to those used in the loaded intervention groups. Perceived exertion and symptom responses will be documented during each session.
Diaphragm thickening fraction
Diaphragm thickness will be assessed using a portable ultrasound device (VERSANA PREMIER) operating in B-mode with a 10-MHz linear transducer. Standardized imaging settings, including gain, depth, and focus, were maintained throughout all examinations. Ultrasound measurements were conducted by a trained assessor who was blinded to participants' group assignments. With participants positioned supine, the transducer was placed over the right hemidiaphragm at the zone of apposition, located between the anterior and mid-axillary lines at the eighth to ninth intercostal space. Care was taken to apply minimal pressure with the probe to prevent compression of underlying tissues. Diaphragm thickness measurements were obtained at end-expiration, corresponding to residual volume (RV), and at end-inspiration, corresponding to total lung capacity (TLC). Each measurement was repeated three times with a minimum rest period of 30 seconds between trials, and the mean value was used for analysis.
Maximal inspiratory pressure
MIP will be measured using a calibrated respiratory pressure manometer in the supported sitting position. Participants will exhale to residual volume and perform maximal inspiration against an occluded airway. At least three maneuvers will be performed with ≥30 seconds rest, and the highest reproducible value will be recorded in cmH₂O.
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