Author(s): FORJAZ, C., SANTOS, M., DORNELAS, W., ALBINO, S., COELHO, T., DA SILVA JUNIOR, N., COSTA, L., LOW, D., BRITO, L., RAMIRES, P., Institution: UNIVERSITY OF SAO PAULO, Country: BRAZIL, Abstract-ID: 762

INTRODUCTION:
Bright light directed to the eyes can change cardiovascular responses to exercise (1,2). In clinical practice, indoor light usually comes from a source in the ceiling, not only impacting the eyes but also hitting the skin, which can change its physiological effects. Therefore, this study was designed to evaluate whether indoor light intensity can change cardiovascular responses to exercise.
METHODS:
Twenty-nine healthy young men participated in two experimental sessions conducted in random order: dim light (DL, 8 lx) and bright light (BL, 5,000 lx). In each session, blood pressure (BP - auscultatory), heart rate (HR - ECG), HR varibility (HRV – spectral analysis) and brachial vascular conductance (BVC - ultrasound) were measured at supine rest in three time-points: under control light before the exercise (CON, 500 lx), under the experimental light pre-exercise (PRE) and under the experimental light for 40 min post- exercise (POST). Additionally, BP, HR, and oxygen uptake (VO2) were measured during exercise in both sessions. The exercise bout consisted of a progressive maximal exercise test conducted on a cycle ergometer with increments of 20W/min until volitional exhaustion. Maximal values obtained during the exercise were compared between the sessions using paired t-tests. Pre and post-exercise data were analyzed by two-way repeated measures ANOVAs, with session (BL and DL) and time-point (CON, PRE, and POST) as the main factors. Post-hoc comparisons were conducted by Bonferroni tests, and P<0.05 was considered significant.
RESULTS:
Maximal BP, HR, and VO2 were similar in BL and DL sessions (all P>0.05). BP, HR, and HRV did not change from CON to PRE in both sessions. Post-exercise, mean BP, HR, and cardiac sympathovagal balance increased similarly in both sessions (all Pmoment<0.001). On the other hand, BVC decreased from CON to PRE only in the DL session, and increased from PRE to POST in both sessions but with a greater increase in the DL session, meaning post-exercise BVC was similar in both sessions (lnBVC, DL= 0.61±0.46 vs. -0.18±0.29 vs. 0.49±0.31 and BL= 0.38±0.54 vs. 0.36±0.52 vs. 0.72±0.51, Pinteraction<0.001).
CONCLUSION:
Indoor light intensity does not affect BP, HR or cardiac autonomic modulation before, during, and after maximal exercise, but exposure to DL reduces BVC at rest and potentiates its increase after an exercise bout.
Financial Support: CNPQ (302309/2022-5) and CAPES (0001)
References:
1. Oliveira et al., 2024. Physiological Reports. doi: 10.14814/phy2.16141
2. Marin et al., 2025. Chronobiology International. doi: 10.1080/07420528.2025.2556841