High- and Moderate-Intensity Inspiratory Muscle Training on Diaphragm Ultrasound Parameters, Cognition, and Mental Health

Low skeletal muscle mass during young adulthood has become an increasingly recognized public health concern because it is associated with reduced physical performance, impaired metabolic health, and an increased risk of developing sarcopenia later in life. In addition to peripheral skeletal muscles, reduced muscle mass may affect diaphragm structure and function, potentially contributing to impaired respiratory mechanics as well as alterations in cognition, sleep, psychological well-being, and health-related quality of life. Although inspiratory muscle training (IMT) has been widely used to improve inspiratory muscle performance, the influence of different IMT intensities on diaphragm morphology and multidimensional health outcomes has not been fully established.

This randomized, sham-controlled clinical trial is designed to compare the effects of high-intensity inspiratory muscle training (HI-IMT), moderate-intensity inspiratory muscle training (MI-IMT), and sham inspiratory muscle training in young adults with low skeletal muscle mass. The primary objective is to determine whether training intensity influences changes in diaphragm structure and function assessed by ultrasonography. Secondary objectives are to evaluate the effects of different IMT intensities on cognitive function, sleep quality, daytime sleepiness, insomnia severity, anxiety, and health-related quality of life.

Participants aged 18-25 years with low skeletal muscle mass will be randomly assigned to one of three parallel groups using age- and sex-stratified block randomization. Participants allocated to the HI-IMT group will perform inspiratory muscle training at approximately 80% of maximal inspiratory pressure (MIP), whereas participants in the MI-IMT group will train at approximately 50-60% of MIP. Participants in the sham group will perform inspiratory muscle training using minimal resistance (approximately 15% of MIP). The intervention will last 6 weeks, with five training sessions per week. One session each week will be supervised by a physiotherapist, and the remaining sessions will be completed at home with regular monitoring.

Outcome assessments will be performed before and after the intervention. Primary outcome measures will include diaphragm thickness, diaphragm thickening fraction, and diaphragm excursion assessed using ultrasonography. Secondary outcome measures will include body composition, cognitive function assessed using the Montreal Cognitive Assessment (MoCA), sleep quality assessed using the Pittsburgh Sleep Quality Index (PSQI), daytime sleepiness assessed using the Epworth Sleepiness Scale (ESS), insomnia severity assessed using the Insomnia Severity Index (ISI), anxiety assessed using the State-Trait Anxiety Inventory (STAI) and the Generalized Anxiety Disorder-7 (GAD-7), and health-related quality of life assessed using the Short Form-36 Health Survey (SF-36).

The study is designed to evaluate whether different inspiratory muscle training intensities are associated with differences in diaphragm morphology and function, cognitive function, sleep, anxiety, and health-related quality of life in young adults with low skeletal muscle mass.

Inclusion criteria

• Young adults aged 18 to 25 years.
• Low skeletal muscle mass defined as a skeletal muscle mass index (SMI) < 8.87 kg/m² for men and < 6.42 kg/m² for women.
• Clinically stable and able to safely participate in inspiratory muscle training.
• Willing and able to provide written informed consent.
• Able to comply with the study procedures and complete all assessments.

Exclusion criteria

• Presence of cardiovascular, neurological, orthopedic, psychiatric, respiratory, or other systemic diseases that could influence study outcomes.
• History of surgery that could affect participation or outcome assessments.
• Cognitive, psychological, or mental conditions that could interfere with participation or completion of the assessments.
• Inability or unwillingness to complete the intervention protocol or follow-up assessments.
• Any contraindication to inspiratory muscle training as determined by the investigators.