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

Low skeletal muscle mass during young adulthood may impair diaphragm function, cognition, sleep, and psychological well-being. Inspiratory muscle training (IMT) has been shown to improve respiratory muscle performance; however, it remains unclear whether different IMT intensities produce differential effects on diaphragm morphology and function, cognition, sleep, anxiety, and health-related quality of life.

The purpose of this randomized controlled trial is 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.

A total of 69 participants with low skeletal muscle mass will be randomly assigned to one of three groups: (1) HI-IMT, (2) MI-IMT, or (3) sham IMT. Participants will complete a supervised 6-week intervention consisting of five training sessions per week.

Participants allocated to the HI-IMT group will perform inspiratory muscle training at approximately 80% of maximal inspiratory pressure (MIP), whereas those in the MI-IMT group will train at approximately 50-60% of MIP. The sham group will perform low-intensity inspiratory muscle training at approximately 15% of MIP. Training intensity will be adjusted throughout the intervention according to repeated MIP assessments.

Outcome assessments will be performed before and after the intervention. Primary outcomes will include diaphragm thickness, diaphragm thickening fraction, and diaphragm excursion assessed using ultrasonography. Secondary outcomes will include 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 health-related quality of life assessed using the Short Form-36 Health Survey (SF-36).

The primary hypothesis is that both HI-IMT and MI-IMT will improve diaphragm morphology and function, cognition, sleep, anxiety, and health-related quality of life compared with sham IMT. It is further hypothesized that HI-IMT will produce greater improvements than MI-IMT because of the higher inspiratory training intensity.