Author(s): KLEEMANN, S., NICKEL, Z., EGBRING, C., MALISZEWSKI, K., SCHRÖTER, T., HEIDUSCHKA, P., GARBSCH, R., ETER, N., ALTEN, F., STORP, J.J., SCHMITZ, B. , Institution: UNIVERSITY OF WITTEN/HERDECKE, Country: GERMANY, Abstract-ID: 2702

INTRODUCTION:
Although zone 1 aerobic training forms the foundation of endurance performance and cardiovascular health promotion, its acute microvascular effects remain poorly understood. Optical coherence tomography angiography (OCT-A) is a non-invasive imaging tool that visualises retinal capillary networks and OCT-A may provide insights into systemic microvascular adaptations during physical activity. However, it remains unclear whether physical stress alters retinal capillary structures and to what extent the eye could be used to monitor whole-body vascular responses.

The aim of this study was to determine whether standardized one-hour aerobic threshold running induces detectable structural changes in the retinal and choroidal microvasculature, and to evaluate the potential of OCT-A as a translational imaging biomarker linking ocular and systemic microvascular physiology (n=104 eyes).
METHODS:
Fifty-two moderately trained recreational runners from (age: 32± 10 years, Yo-Yo test: 933±415 m; VO₂ max: 44.2±3.5 ml/kg/min) completed a one-hour running training session in Zone 1, monitored using Garmin Vivosmart. Lactate analyses were performed before and after the run to evaluate the metabolic state. The superficial capillary plexus (SCP) and choroid were examined immediately before and after training using a Canon Xephilio S1 wide-angle swept-source OCT A (23 × 20 mm²). To extract the flow parameters from the image, Angio Tool software was applied, followed by quantitative analyses using paired t-tests in GraphPad Prism.

RESULTS:
Individualized Zone 1 running produced moderate aerobic stress, as confirmed by lactate levels (pre: 1.83 mmol/L ± 1.66 vs. post: 2.24 mmol/L ± 2.01; P = 0.22) and heart rate maintenance within the aerobic training zone (average HR: 140 ± 10, minimum HR: 122 ± 14, maximum HR: 157 ± 10). Widefield OCT-A revealed no significant structural capillary remodelling post-exercise. Metrics of the superficial capillary plexus remained stable (all p > 0.11). Corresponding choroidal parameters showed equivalent stability (all p > 0.37). Excellent measurement reproducibility confirmed the robustness of the methodology (pre-post correlations: r = 0.50–0.75; all p < 0.0001).
CONCLUSION:
Individualized Zone 1 running preserved retinal and choroidal capillary architecture despite verified physiological training stress, demonstrating robust microvascular autoregulation during foundational endurance training. Widefield OCT-A revealed no detectable structural capillary remodeling, establishing the retina as stable reference for exercise microvascular studies. This translational approach validates OCT-A as non-invasive imaging tool to monitor training-induced microvascular adaptations. Future investigations may identify Zone 1 thresholds beyond which retinal capillary remodeling occurs.