Acute Effects of Functional Inspiratory Muscle Training on Exercise Capacity, Muscle Oxygenation, Balance, and Agility in Elite Male Volleyball Players

This prospective, randomized, controlled, parallel-group interventional study is designed to investigate the acute effects of a single session of functional inspiratory muscle training on muscle oxygenation, functional exercise capacity, dynamic balance, and agility in elite male volleyball players aged 18 to 25 years. The study is conducted at the Cardiopulmonary Rehabilitation Unit, Department of Physiotherapy and Rehabilitation, Faculty of Health Sciences, Gazi University. A total of 30 participants are planned, with 15 participants allocated to the functional inspiratory muscle training group and 15 participants allocated to the no-intervention control group.

After eligibility screening and written informed consent, participants are randomly assigned to the study groups in a 1:1 ratio. The computer-generated allocation sequence is created using the Sealed Envelope online randomization service. Outcome assessments are performed by physiotherapists who are not informed of group allocation. Participants and the personnel administering the training cannot be masked because participants in the intervention group use a POWERbreathe inspiratory muscle training device, whereas participants in the control group receive no sham inspiratory muscle training. Therefore, the study uses single masking at the level of the outcome assessor. When feasible, the statistician will receive the dataset with the treatment groups coded.

Before the training session, maximal inspiratory pressure is measured in the intervention group using a mouth pressure meter to determine the individual training resistance. Participants are assessed in a seated position while wearing a nose clip and maintaining a complete seal around the mouthpiece. After a complete expiration to residual volume, participants are instructed to perform a maximal inspiratory effort. At least three acceptable maneuvers are performed, with a 30-second rest period between maneuvers. When the difference between repeated measurements is less than 10%, the highest value is recorded as maximal inspiratory pressure in cmH2O. The training resistance is set at 50% of the individual maximal inspiratory pressure. Because maximal inspiratory pressure is measured only to determine the intervention dose and is not assessed before and after the study period in both groups, it will not be treated as a comparative study outcome.

Following warm-up, participants in the intervention group perform functional inspiratory muscle training using a POWERbreathe pressure-threshold device while completing a sport-specific fixed-ball throwing drill. The session consists of two sets of 30 resisted inspirations, corresponding to a total of 60 breaths. The session lasts approximately 10 to 12 minutes. Inspiration is performed against a resistance equivalent to 50% of the participant's maximal inspiratory pressure, whereas expiration is unrestricted. The training is integrated into the throwing drill without intentionally interrupting the participant's sport-specific movement pattern. Participants in the control group receive no inspiratory muscle training or sham respiratory intervention and undergo the same pre-intervention and post-intervention outcome assessments.

All outcome assessments are conducted before and immediately after the single-session intervention or corresponding control period on the same day. The post-intervention assessments are intended to determine the immediate acute response to the training session. The main muscle oxygenation outcomes are quadriceps muscle oxygen saturation and total hemoglobin. Functional exercise capacity, dynamic balance, and agility are evaluated as additional outcomes.