Acute Effects of Functional Inspiratory Muscle Training in Elite Male Volleyball Players

This prospective, randomized, controlled, parallel‐group interventional study is designedto investigate the acute effects of a single session of functional inspiratory muscletraining on muscle oxygenation, functional exercise capacity, dynamic balance, andagility in elite male volleyball players aged 18 to 25 years. The study is conducted atthe Cardiopulmonary Rehabilitation Unit, Department of Physiotherapy and Rehabilitation,Faculty of Health Sciences, Gazi University. A total of 30 participants are planned, with15 participants allocated to the functional inspiratory muscle training group and 15participants allocated to the no‐intervention control group.After eligibility screening and written informed consent, participants are randomlyassigned to the study groups in a 1:1 ratio. The computer‐generated allocation sequenceis created using the Sealed Envelope online randomization service. Outcome assessmentsare performed by physiotherapists who are not informed of group allocation. Participantsand the personnel administering the training cannot be masked because participants in theintervention group use a POWERbreathe inspiratory muscle training device, whereasparticipants 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, thestatistician will receive the dataset with the treatment groups coded.Before the training session, maximal inspiratory pressure is measured in the interventiongroup using a mouth pressure meter to determine the individual training resistance.Participants are assessed in a seated position while wearing a nose clip and maintaininga complete seal around the mouthpiece. After a complete expiration to residual volume,participants are instructed to perform a maximal inspiratory effort. At least threeacceptable maneuvers are performed, with a 30‐second rest period between maneuvers. Whenthe difference between repeated measurements is less than 10%, the highest value isrecorded as maximal inspiratory pressure in cmH2O. The training resistance is set at 50%of the individual maximal inspiratory pressure. Because maximal inspiratory pressure ismeasured only to determine the intervention dose and is not assessed before and after thestudy period in both groups, it will not be treated as a comparative study outcome.Following warm‐up, participants in the intervention group perform functional inspiratorymuscle training using a POWERbreathe pressure‐threshold device while completing asport‐specific fixed‐ball throwing drill. The session consists of two sets of 30 resistedinspirations, corresponding to a total of 60 breaths. The session lasts approximately 10to 12 minutes. Inspiration is performed against a resistance equivalent to 50% of theparticipant's maximal inspiratory pressure, whereas expiration is unrestricted. Thetraining is integrated into the throwing drill without intentionally interrupting theparticipant's sport‐specific movement pattern. Participants in the control group receiveno inspiratory muscle training or sham respiratory intervention and undergo the samepre‐intervention and post‐intervention outcome assessments.All outcome assessments are conducted before and immediately after the single‐sessionintervention or corresponding control period on the same day. The post‐interventionassessments are intended to determine the immediate acute response to the trainingsession. The main muscle oxygenation outcomes are quadriceps muscle oxygen saturation andtotal hemoglobin. Functional exercise capacity, dynamic balance, and agility areevaluated as additional outcomes.Local muscle oxygenation is monitored noninvasively using a portable Moxy near‐infraredspectroscopy device positioned over the midpoint of the right quadriceps femoris muscle.The placement site will be kept consistent between the pre‐intervention andpost‐intervention assessments. The Moxy device continuously records muscle oxygensaturation, expressed as a percentage, and total hemoglobin, expressed in g/dL.Recordings are obtained during three prespecified phases: rest before the IncrementalShuttle Walk Test, exercise during the Incremental Shuttle Walk Test, and recovery aftertest termination. For each assessment, muscle oxygen saturation and total hemoglobin willbe summarized over predefined rest, exercise, and recovery analysis epochs. The beginningand end of each analysis epoch and the summary metric used for that epoch will bedetermined in the statistical analysis plan before outcome analysis. Pre‐to‐post changesin these muscle oxygenation measures will be compared between the intervention andcontrol groups.Functional exercise capacity is assessed using the Incremental Shuttle Walk Test on a10‐meter course. Participants walk back and forth between two markers in accordance withexternally generated audio signals. Walking speed increases by approximately 0.17 m/severy minute. The test is terminated when the participant is unable to maintain therequired pace, cannot follow the audio signals, or stops because of limiting fatigue orsymptoms. The total distance completed is recorded in meters. A greater distancerepresents better functional exercise capacity. The pre‐intervention to post‐interventionchange in total distance will be compared between groups.Dynamic balance and postural control are assessed using the Star Excursion Balance Test.The participant stands on the dominant leg and reaches as far as possible with theopposite leg in eight directions separated by 45‐degree intervals. Three trials areperformed in each direction. The longest valid reach distance in each direction isrecorded in centimeters. Reach distance is normalized to limb length using the followingcalculation: normalized reach distance (%) = reach distance (cm) divided by limb length(cm), multiplied by 100. Higher normalized values indicate better dynamic balance.Direction‐specific pre‐to‐post changes will be compared between the intervention andcontrol groups.Agility is assessed using the T‐Test. The participant completes a 40‐meter movementsequence involving forward running, lateral shuffling to both sides, and backward runningwhile remaining oriented in the same direction. The course includes two 90‐degree changesof direction and one 180‐degree change of direction. Completion time is recorded inseconds using the same timing method at the pre‐intervention and post‐interventionassessments. The fastest valid completion time obtained under the study protocol is usedfor analysis. A shorter completion time indicates better agility performance. Thepre‐to‐post change in completion time will be compared between groups.Statistical analyses will be performed using IBM SPSS Statistics version 25 with areproducible syntax file. Participant characteristics and baseline measurements will besummarized by randomized group. Normally distributed continuous variables will bepresented as mean and standard deviation, non‐normally distributed variables as medianand interquartile range or minimum‐maximum values, and categorical variables asfrequencies and percentages. Baseline significance testing will not be used to determinewhether randomization was successful.Participants will be analyzed according to their randomized groups. The principaltreatment effect will be the difference in pre‐intervention to post‐intervention changebetween the intervention and control groups. This effect will be tested using thegroup‐by‐time interaction rather than separate within‐group significance tests.For Incremental Shuttle Walk Test distance and T‐Test completion time, the primaryanalysis will use a 2 × 2 mixed‐design repeated‐measures analysis of variance, with groupas the between‐participant factor and time as the within‐participant factor. Thegroup‐by‐time interaction will represent the acute effect of functional inspiratorymuscle training.Muscle oxygen saturation and total hemoglobin will be analyzed separately using modelsthat include group, time, and measurement phase. Group will include the intervention andcontrol groups, time will include the pre‐intervention and post‐intervention assessments,and phase will include rest, exercise, and recovery. The group‐by‐time interaction willdetermine whether the overall pre‐to‐post response differs between the groups. Thegroup‐by‐time‐by‐phase interaction will determine whether the training response differsacross the rest, exercise, and recovery phases. The primary muscle oxygenation contrastwill be the between‐group difference in pre‐to‐post change during the prespecifiedexercise phase. Because muscle oxygen saturation and total hemoglobin are treated as tworelated primary oxygenation outcomes, their primary probability values will be adjustedusing the Holm procedure.Normalized Star Excursion Balance Test reach distances will be analyzed using a modelthat includes group, time, and reach direction. The group‐by‐time interaction willevaluate the overall balance response, and the group‐by‐time‐by‐direction interactionwill determine whether the response differs among the eight reach directions.Direction‐specific follow‐up comparisons will be performed only when supported by thecorresponding interaction and will be adjusted for multiple comparisons.When a statistically significant interaction is identified, prespecified simple‐effectscomparisons of estimated marginal means will be performed with Bonferroni adjustment, asappropriate. Results will be reported using pre‐intervention and post‐interventionvalues, mean within‐group changes, the between‐group difference in change, 95% confidenceintervals, exact two‐sided p values, and partial eta‐squared effect sizes. Statisticalsignificance will be set at a two‐sided p value below 0.05 after any applicablemultiplicity adjustment.Model residuals will be evaluated using graphical methods, including Q‐Q plots, and theShapiro‐Wilk test when appropriate. Homogeneity of variance will be assessed usingLevene's test. For models containing more than two repeated levels, sphericity will beevaluated using Mauchly's test, and Greenhouse‐Geisser‐corrected results will be reportedwhen the sphericity assumption is violated. If substantial deviations from the modelassumptions are identified, appropriately transformed outcomes, robust analyses, orrank‐based sensitivity analyses will be considered.A baseline‐adjusted analysis of covariance, with the post‐intervention value as thedependent variable and the corresponding baseline value as a covariate, will be performedas a sensitivity analysis for the principal outcomes. If repeated outcome measurementsare incomplete, a linear mixed‐effects model using all available observations will beused as an additional sensitivity analysis under a missing‐at‐random assumption. Becauseof the limited sample size, no data��driven subgroup analysis or extensive covariateselection is planned.The study was designed and conducted as a prospective randomized interventional study.However, registration occurred after participant enrollment had begun. Therefore, theregistration is retrospective in relation to the beginning of enrollment, although thestudy design itself is not retrospective. The date of first participant enrollment andthe reason for delayed registration will be reported transparently.