Effects of Inspiratory Training on Respiratory Function in Swimming

Effects of Inspiratory Training on Respiratory Function, Diaphragmatic Structure, and Cardiac Response in Healthy Adults During Aquatic Exercise.

Introduction:

The diaphragm is the primary inspiratory muscle and plays a key role in ventilation, trunk stability, and exercise efficiency. Its dysfunction is associated with early fatigue, increased respiratory work, and reduced performance. Inspiratory muscle training (IMT) has been shown to improve respiratory function and exercise tolerance. Swimming, due to its specific characteristics, imposes an additional demand on the respiratory muscles.

Objective:

To evaluate the effects of an IMT program on diaphragmatic function, respiratory variables, cardiorespiratory response, and performance in swimmers.

Methods:

A randomized, parallel, double-blind clinical trial with 34 swimmers. The experimental group will perform an 8-week IMT program with progressive loads, while the control group will use a sham device without resistance. Diaphragmatic function will be assessed using ultrasound (thickness and excursion), along with respiratory variables (MIP, FEV₁, MEP, FVC), cardiovascular variables (heart rate, HRV), metabolic variables (lactate), and performance (100 m test).

Expected results:

IMT is expected to improve diaphragmatic function, increase inspiratory muscle strength, enhance ventilatory efficiency, and reduce respiratory fatigue, leading to improvements in performance and physiological responses to exercise.

Conclusion:

IMT could be an effective strategy to enhance respiratory function and swimming performance. This study provides a novel approach by incorporating ultrasound assessment of the diaphragm in an aquatic exercise context.

Study Overview

• Status: Enrolling by invitation
• Conditions: Inspiratory Muscle Training; Swimming; Inspiratory Muscle Strength
• Intervention / Treatment: Device: Inspiratory training; Device: Placebo

Detailed Description

Diaphragm

The diaphragm is the primary muscle of inspiration. It is a dome-shaped skeletal muscle located between the thoracic and abdominal cavities. Its contraction increases thoracic volume, allowing air to enter the lungs. Beyond respiration, it contributes to core stability and postural control during movement and exercise.

Inspiratory Muscle Training (IMT)

IMT is a training method that involves breathing against a resistive load to strengthen the inspiratory muscles, mainly the diaphragm and accessory muscles. It is used to improve respiratory strength, endurance, and ventilatory efficiency, especially in athletes and clinical populations.

Respiratory function

Respiratory function refers to the ability of the respiratory system to ventilate, exchange gases, and maintain adequate oxygen and carbon dioxide levels. It is commonly assessed using spirometric and pressure-based measures.

Diaphragmatic dysfunction

This refers to a reduced ability of the diaphragm to generate force or excursion, leading to impaired ventilation. It may result in increased breathing effort, reduced exercise tolerance, and earlier onset of respiratory fatigue.

Maximal Inspiratory Pressure (MIP)

MIP is the maximum negative pressure generated during a forceful inspiration against an occluded airway. It is a key indicator of inspiratory muscle strength, especially diaphragmatic function.

Forced Expiratory Volume in 1 second (FEV₁)

FEV₁ is the volume of air that can be forcefully exhaled in the first second of a forced expiration. It is a standard measure of airway function and pulmonary performance.

Maximal Expiratory Pressure (MEP)

MEP represents the maximum pressure generated during a forceful expiration. It reflects the strength of expiratory muscles such as abdominal and intercostal muscles.

Forced Vital Capacity (FVC)

FVC is the total volume of air exhaled forcefully after a maximal inspiration. It reflects lung capacity and ventilatory function.

Heart rate

Heart rate is the number of heartbeats per minute. It reflects cardiovascular response to exercise intensity and autonomic nervous system activity.

Heart Rate Variability (HRV)

HRV is the variation in time intervals between consecutive heartbeats. It is a marker of autonomic nervous system balance, particularly sympathetic and parasympathetic activity.

Blood lactate

Blood lactate is a metabolic byproduct of anaerobic glycolysis. Elevated levels indicate increased reliance on anaerobic energy systems and higher metabolic stress during intense exercise.

100-meter swimming test

A standardized performance test measuring the time required to complete 100 meters freestyle swimming at maximal effort. It is used to assess anaerobic and aerobic performance capacity in swimmers.

Randomized controlled trial (RCT)

An experimental study design in which participants are randomly assigned to different intervention groups to reduce bias and ensure comparability.

Parallel design

A study design where two or more groups are followed simultaneously, each receiving a different intervention throughout the study period.

Double-blind design

A methodological approach in which neither participants nor researchers know group allocation, minimizing expectation and measurement bias.

Sham device (placebo IMT)

A device designed to mimic IMT without providing meaningful resistance, used to control for placebo effects in training studies.

Ultrasound assessment

A non-invasive imaging technique used to evaluate diaphragm structure and function in real time, including thickness and movement during breathing.

Diaphragmatic thickness

The measurement of the muscle layer of the diaphragm, often assessed at rest and during contraction to evaluate contractile capacity.

Diaphragmatic excursion

The movement amplitude of the diaphragm during breathing, reflecting its functional mobility and efficiency.

• Study Type: Interventional
• Enrollment (Estimated): 34
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Spain
  • Madrid, Spain
    • Club de natación Moscardó

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Participants of both sexes, aged over 18 years.
• Minimum swimming training frequency of at least two sessions per week, with a minimum duration of 30 minutes per session, consistently maintained over the last three months.

Exclusion Criteria:

• Current or previous diagnosis of respiratory diseases.
• Musculoskeletal injuries limiting the ability to perform a 100-meter swimming test.
• Participation in inspiratory muscle training programs within the last six months.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Inspiratory training; The experimental group will perform an eight-week home-based training program using the POWERbreathe EX1-MR device, individually calibrated according to MIP. Participants will complete 30 deep inspirations per session, twice daily, seven days per week, with progressive intensities: 30% of initial MIP during weeks 1-2, 50% of the new MIP during weeks 3-4, 60% during weeks 5-6, and 70% of MIP during weeks 7-8, with the aim of familiarizing participants with the device and progressively adapting the diaphragm to increasing loads.	Device: Inspiratory training; The experimental group will perform an eight-week home-based training program using the POWERbreathe EX1-MR device, individually calibrated according to MIP. Participants will complete 30 deep inspirations per session, twice daily, seven days a week, with progressive intensities: 30% of initial MIP during weeks 1-2, 50% of the new MIP during weeks 3-4, 60% during weeks 5-6, and 70% of MIP during weeks 7-8, with the aim of familiarizing participants with the device and progressively adapting the diaphragm to increasing loads.
Placebo Comparator: Placebo; The control group will use the same device without resistance, maintaining the same breathing frequency and volume in order to control for the placebo effect.	Device: Placebo; The control group will use the same device without resistance, maintaining the same breathing frequency and volume to control for the placebo effect.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Sport performance	Total time and split times for completing 100 m freestyle.	This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Maximal inspiratory pressure.	Inspiratory variables: Inspiratory muscle strength was assessed by measuring MIP using the POWERbreathe Smart Adaptor device. The participant was seated and used a mouthpiece with a leak hole to minimize activation of the orofacial musculature. The procedure consisted of a maximal expiration to residual volume, followed by a maximal inspiration sustained against the device for at least 2 seconds. Three attempts were performed with rest periods of at least 1 minute, and the highest value was selected.	This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Maximal espiratory pressure.	Expiratory variables: Pulmonary function was assessed using forced spirometry, recording FEV₁, MEP, and FVC with the MIR Spirobank Oxi Portable Spirometer device. For a manoeuvre to be acceptable, the subject had to perform a maximal inspiration followed by a rapid and continuous forced expiration, without coughing during the first second and with a smooth flow-volume curve, without leaks. The expiration had to last at least 6 seconds or until a volume plateau was reached. Manoeuvres with interruptions, false efforts, or closed glottis were discarded. Three acceptable manoeuvres were performed, and results were considered valid when the two best FEV₁ and FVC values differed by less than 150 mL. If this variability criterion was not met, additional attempts were performed until reproducible results were obtained.	This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
lactate	It will be taken from the fingertip immediately after completing the test, following the extraction protocol to ensure measurement validity. The device will be calibrated before each testing session according to the manufacturer's recommendations.	This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Perceived exertion.	The Borg scale (6-20) will be previously explained to the participant using standardized instructions to ensure full understanding. Perceived intensity will be recorded immediately after the test through a direct interview with the evaluator.	This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Dysnea	It will be administered verbally and individually by the evaluator immediately after physical exertion, ensuring that the participant understands each item. The test consists of 12 questions rated on a 0-3 Likert scale for each item.	This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Heart rate.	It will be placed on the anterior thoracic region, just below the xiphoid process. The device will be calibrated and checked according to the manufacturer's instructions before each test. Heart rate will be recorded in real time from the start until five minutes after the test. Data will be analyzed using Polar Flow software, including mean heart rate (HRmean), maximum heart rate (HRmax), recovery time (RT), and heart rate variability (HRV). The data will then be further analyzed in Polar Flow.	This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Diaphragmatic excursion	It was assessed on the right hemidiaphragm to ensure an adequate acoustic window. The transducer was placed in the anterior subcostal region at the midclavicular line, with a craniocaudal orientation and slight medial angulation. First, B-mode ultrasound was used to identify the diaphragmatic dome as a hyperechoic, mobile line. Subsequently, M-mode was activated, aligning the cursor perpendicular to the diaphragmatic movement, and vertical displacement was recorded from the end of quiet expiration to maximal voluntary inspiration. Three valid manoeuvres were performed, and the highest value was selected for analysis, expressed in centimeters.	This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Diaphragmatic thickening	It was assessed by placing the transducer in the diaphragm's zone of apposition, located between the 8th and 10th intercostal spaces along the midaxillary line. In B-mode, the diaphragm was identified as a hypoechoic structure bounded by two hyperechoic lines corresponding to the pleura and peritoneum. Diaphragmatic thickness was measured at the end of quiet expiration and during maximal voluntary inspiration. Three consecutive respiratory cycles were recorded, and the mean value was used for final analysis.	This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.

Collaborators and Investigators

• Sponsor: Universidad Rey Juan Carlos
• Investigators: Principal Investigator: Agustin c Velazquez, Universidad Rey Juan Carlos

Study record dates

Study Major Dates

• Study Start (Estimated): September 1, 2026
• Primary Completion (Estimated): December 1, 2026
• Study Completion (Estimated): January 1, 2027

Study Registration Dates

• First Submitted: April 18, 2026
• First Submitted That Met QC Criteria: May 12, 2026
• First Posted (Actual): May 19, 2026

Study Record Updates

• Last Update Posted (Actual): May 19, 2026
• Last Update Submitted That Met QC Criteria: May 12, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Keywords: sport performance; IMT; RPE
• Other Study ID Numbers: 150120261552026; Sponsor-Investigator (Other Identifier: Agustín Velázquez Córdoba)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES

IPD Plan Description

Plan description:

At present, no definitive decision has been made regarding the sharing of individual participant data. The possibility of sharing anonymized data with other researchers is being considered in order to promote scientific transparency, reproducibility of results, and the development of future research.

However, this decision will be subject to strict compliance with applicable data protection regulations (GDPR), the safeguarding of participant confidentiality, and the evaluation of the sample size and the specific context of the study.

If data are shared, they will be provided exclusively in anonymized format, upon justified request and under formal data use agreements.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No