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

Overview

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.

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.

Interventions

• 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.

Primary outcome measures

• 1. Intraocular Pressure (IOP) [Time frame: 3 days]
• 2. Retinal Microcirculation [Time frame: 3 days]
• 3. Blood pressure (BP) [Time frame: 3 days]
• 4. Oxygen Saturation (SpO₂) [Time frame: 3 days]
• 5. Eye Dryness [Time frame: 3 days]
• 6. Anthropometric Data [Time frame: 3 days]
• Questionaire no. 1 [Time frame: 3 days]
• Questionnaire no.2 [Time frame: 3 days]
• Questionnaire no. 3 [Time frame: 3 days]

Eligibility criteria

Inclusion criteria

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

Exclusion criteria

• Presence of any ocular disease (with the exception of refractive errors)
• Anxiety or depressive disorders
• History of ocular trauma or surgery
• Pregnancy
• Use of any kind of oral/topical steroids
• Any diagnosed chronic health condition such as cardiovascular disease including hypertension and or previous physical injuries that could impact their safe participation
• 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.
• Refractive error more than ±4.00 diopters, astigmatism greater than 3.00 diopters.

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Triple blind

Primary purpose

Basic science

Study locations

Center list to be confirmed — check the primary protocol.

Identifiers

NCT: NCT07326462 · LithuanianSportsU-27

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗