The Effects of Strength Training Volume, Intensity, and Breathing Techniques on Intraocular Pressure and Retinal Blood Vessels

This study aims to determine the effects of different breathing patterns on ocular vasculature and intraocular pressure (IOP) during isokinetic and isometric strength exercises. It is hypothesized that higher ocular microcirculation changes and IOP values will be observed during the Valsalva maneuver compared to normal breathing in both exercise types. Additionally, ocular microcirculation and IOP changes are expected to be more pronounced during isometric exercises than during isokinetic exercises. The results will help establish optimal strength training strategies for both professional athletes and physically active individuals.

Study Overview

• Status: Not yet recruiting
• Conditions: Healthy Participants
• Intervention / Treatment: Diagnostic test: Normal Breathing; Diagnostic test: Valsalva maneuver

Detailed Description

This study is a randomized controlled trial designed to evaluate the effects of different breathing patterns on ocular vasculature and intraocular pressure (IOP) during isokinetic and isometric strength exercise in healthy young adults.

The study protocol was approved by the Kaunas Regional Biomedical Research Ethics Committee, and all participants provided written informed consent prior to participation, in accordance with the Declaration of Helsinki.

Participants will attend experimental sessions during which ocular and cardiovascular parameters will be assessed before exercise, immediately after exercise, and during the recovery period.

Baseline assessments will include general anthropometric measurements and questionnaires related to physical activity and fatigue, as well as evaluation of ocular surface condition.

Retinal microcirculation will be assessed using non-mydriatic fundus photography, and intraocular pressure will be measured using a portable tonometry method. Blood pressure and oxygen saturation will also be monitored during study sessions.

Each participant will perform a standardized 1-minute strength exercise under two exercise modalities: isokinetic and isometric. A standardized warm-up will precede each exercise session.

Two breathing conditions will be evaluated during exercise: normal breathing and the Valsalva maneuver. The order of exercise modality and breathing condition will be randomized, and experimental sessions will be separated by an adequate washout period.

The planned sample size was determined a priori based on statistical power considerations to ensure adequate power to detect meaningful differences between study conditions.

Data will be analyzed using appropriate statistical methods. Descriptive statistics will be used to summarize study data. Normality of data distribution will be assessed, and non-parametric methods will be applied when appropriate. Repeated-measures and between-condition comparisons will be conducted, with adjustments for multiple comparisons applied as needed. Statistical significance will be set at p < 0.05.

• Study Type: Interventional
• Enrollment (Estimated): 60
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Monika Vieversyte-Dvyliene, MD; Phone Number: 069031331; Email: monikavieversyte@gmail.com

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

1. Subjects 18-40 years old
2. Peak IOP <21 mmHg in the modified DTC
3. Open angle at gonioscopy
4. Optic disc with cup-to-disc ratio <0.6 with no signs of glaucomatous neuropathy
5. Not currently taking any medication
6. Non-smokers, no physical and mental disabilities
7. Blood pressure up 120/80 mmHg and heart rate (HR) 60-90 rpm at rest
8. BMI (18.5-34.8) kg/m2

Exclusion Criteria:

1. Presence of any ocular disease (with the exception of refractive errors)
2. Anxiety or depressive disorders
3. History of ocular trauma or surgery
4. Pregnancy
5. Use of any kind of oral/topical steroids
6. Any diagnosed chronic health condition such as cardiovascular disease including hypertension and or previous physical injuries that could impact their safe participation
7. Evidence of ocular pathology due to narrow anterior chamber angles, elevated IOP greater than or equal to 21mm Hg, optic nerve or retinal pathology, cup: disc ratio of greater than 0.6 or asymmetry of cup: disc ratio of greater than 0. 2.
8. Refractive error more than ±4.00 diopters, astigmatism greater than 3.00 diopters.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Triple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Isokinetic exercise arm; Protocol: Participants perform a 1-minute maximal voluntary isometric contraction of the knee extensors using a BIODEX dynamometer. Load setting: The maximum isometric load that each individual can sustain for 1 minute is determined during familiarisation. In the main session, participants work at 80% of their predetermined maximum load to avoid premature muscle failure. Nature of exercise: Static contraction (muscle generates force without changing length).	Diagnostic test: Normal Breathing; Participants perform the isometric or isokinetic exercise while following a controlled breathing rhythm: Inhale for 3 seconds Exhale for 3 seconds Breathing remains steady and continuous throughout the 1-minute exercise. Rationale: Represents a natural and safe breathing pattern during physical exertion, serves as the physiological baseline condition.; Diagnostic test: Valsalva maneuver; Participants perform the same isometric or isokinetic exercise but finish the trial with a 10-second breath-hold at the end of the 1-minute exercise. This maneuver increases intrathoracic and intra-abdominal pressures, which are transmitted to ocular and vascular systems. Rationale: Common in athletic performance, but may cause significant intraocular pressure and retinal vascular fluctuations.
Experimental: Isometric exercise arm; Protocol: Participants perform 1 minute of repeated isokinetic knee extensions and flexions at a controlled angular velocity on the BIODEX dynamometer. Velocity settings: Knee extension at 30°/s and knee flexion at 60°/s within the 0°-90° range of motion (0° = full extension). Nature of exercise: Dynamic contraction (muscle changes length while producing force against constant velocity resistance).	Diagnostic test: Normal Breathing; Participants perform the isometric or isokinetic exercise while following a controlled breathing rhythm: Inhale for 3 seconds Exhale for 3 seconds Breathing remains steady and continuous throughout the 1-minute exercise. Rationale: Represents a natural and safe breathing pattern during physical exertion, serves as the physiological baseline condition.; Diagnostic test: Valsalva maneuver; Participants perform the same isometric or isokinetic exercise but finish the trial with a 10-second breath-hold at the end of the 1-minute exercise. This maneuver increases intrathoracic and intra-abdominal pressures, which are transmitted to ocular and vascular systems. Rationale: Common in athletic performance, but may cause significant intraocular pressure and retinal vascular fluctuations.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
1. Intraocular Pressure (IOP)	Tool: Icare portable tonometer (Icare, Tiolat Oy, Helsinki, Finland). Description: Measures the pressure inside the eye, caused by the aqueous humor pressing against the eye wall. Rationale: IOP is a key factor in glaucoma development and progression. Monitoring fluctuations during exercise and different breathing techniques is critical. Timing: Baseline (before exercise), immediately post-exercise, and at 5, 10, 15 minutes after exercise.	3 days
2. Retinal Microcirculation	Tool: Aurora handheld non-mydriatic fundus camera (Optomed, Finland). Description: Digital fundus photography to measure retinal vessel diameters (arterioles and venules) in the superior and inferior temporal quadrants, near the optic disc margin. Rationale: Retinal vessel diameter is a biomarker for cardiovascular health and provides insights into ocular blood flow changes during stress. Timing: Same schedule as IOP (before, immediately after, and 5, 10, 15 minutes post-exercise).	3 days
3. Blood pressure (BP)	Tool: Omron BP742N automatic arm blood pressure monitor (Omron Healthcare, Japan). Description: Monitors systolic and diastolic blood pressure levels. Rationale: To capture systemic cardiovascular responses during isometric vs. isokinetic exercise and different breathing conditions. Timing: Baseline, immediately after, 5, 10, and 15 minutes post-exercise.	3 days
4. Oxygen Saturation (SpO₂)	Tool: Pulse oximeter (Omron). Description: Monitors peripheral blood oxygen levels. Rationale: Evaluates systemic oxygen delivery and breathing effects (especially relevant with Valsalva maneuver). Timing: During the exercise protocol (exact points not deeply detailed in file but implied to match BP).	3 days
5. Eye Dryness	Tool: Schirmer Test (TearFlo strips). Description: Filter paper strips placed inside the lower eyelid for 5 minutes; length of wetting indicates tear production. Rationale: Assesses ocular surface health, as exercise and breathing methods may influence tear production and comfort. Timing: At baseline (before experimental trials).	3 days
6. Anthropometric Data	Tools: Leicester Height Metre for height. Tanita TBF-300 body composition scale for weight and body fat %. Derived Measurement: Body Mass Index (BMI = weight/height²). Rationale: Provides participant characteristics for standardization and analysis.	3 days
Questionaire no. 1	Validated Baecke questionnaire → Physical activity level. Rationale: Captures subjective perception of workload alongside physiological measures.	3 days
Questionnaire no.2	Fatigue assessment questionnaires → Subjective fatigue. Rationale: Captures subjective perception of fatigue alongside physiological measures.	3 days
Questionnaire no. 3	Rating of Perceived Exertion (RPE) → Subjective exercise intensity. Rationale: Captures subjective perception of exertion alongside physiological measures.	3 days

Collaborators and Investigators

• Sponsor: Lithuanian Sports University
• Investigators: Study Director: Vytautas Streckis, phD, Prof., Lithuanian Sports University

Study record dates

Study Major Dates

• Study Start (Estimated): January 1, 2026
• Primary Completion (Estimated): April 1, 2026
• Study Completion (Estimated): May 1, 2026

Study Registration Dates

• First Submitted: December 17, 2025
• First Submitted That Met QC Criteria: January 3, 2026
• First Posted (Actual): January 8, 2026

Study Record Updates

• Last Update Posted (Actual): January 8, 2026
• Last Update Submitted That Met QC Criteria: January 3, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: exercise; intraocular pressure; retinal vessels; Valsalva maneuver
• Additional Relevant MeSH Terms: Behavior; Motor Activity; Diagnostic Techniques and Procedures; Diagnosis; Circulatory and Respiratory Physiological Phenomena; Diagnostic Techniques, Respiratory System; Respiratory Physiological Phenomena; Diagnostic Techniques, Cardiovascular; Heart Function Tests; Respiratory Function Tests; Hemodynamics; Cardiovascular Physiological Phenomena; Valsalva Maneuver
• Other Study ID Numbers: LithuanianSportsU-27

Drug and device information, study documents

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