Combined Inspiratory Muscle Training and Functional High-Intensity Interval Training in Boys With Obesity

This prospective, two-arm, randomized controlled trial investigated the effects of a six-week combined inspiratory muscle training and functional high-intensity interval training program in boys aged 10-12 years with obesity.

Fifty participants were randomly allocated in a 1:1 ratio to either a combined training group or a usual-activity control group. The intervention consisted of progressive inspiratory muscle training performed five days per week and functional high-intensity interval training performed three non-consecutive days per week for six weeks.

Inspiratory muscle training was performed using a threshold pressure-loading device. Training commenced at 30% of maximal inspiratory pressure and increased by 5% each week, reaching 55% of maximal inspiratory pressure in week 6. Each session consisted of two sets of 30 inspiratory efforts.

Functional high-intensity interval training was performed three times per week. Each approximately 35-40-minute session consisted of a standardized warm-up, a functional high-intensity interval circuit, and a cool-down. The circuit included wall sit, incline push-up, seated knee-to-chest exercise, shadow boxing, Superman exercise, and low-step-up exercise. Training intensity was progressively increased by manipulating work-to-rest ratios and circuit volume.

The control group continued habitual daily activities without participating in structured exercise or respiratory muscle training during the six-week study period.

Primary outcomes were diaphragm thickening fraction, inspiratory diaphragm thickness, and expiratory diaphragm thickness. Secondary outcomes included maximal inspiratory pressure, maximal expiratory pressure, forced vital capacity, forced expiratory volume in one second, FEV₁/FVC ratio, six-minute walk distance, estimated VO₂max, body composition, and perceived exertion.

Assessments were performed at baseline and after the six-week intervention under standardized laboratory conditions between 15:00 and 17:00. Diaphragm ultrasonography was performed by a radiologist blinded to group allocation

Inclusion criteria

• Male sex.
• Age 10-12 years.

*Obesity according to World Health Organization age- and sex-specific BMI reference criteria.

• No regular participation in structured exercise training during the preceding six months.
• Medical clearance to participate in moderate-to-vigorous physical activity.

Exclusion criteria

• Diagnosed cardiovascular, neuromuscular, orthopaedic, or metabolic conditions that could interfere with exercise participation.
• Chronic respiratory disease, including asthma requiring regular medication.
• Impaired pulmonary function defined as FEV₁/FVC <75%.

*Upper respiratory tract infection within the preceding two weeks.

• Medication use that could affect respiratory function or exercise capacity.
• Previous thoracic surgery.
• Inability to complete the testing procedures.