Light exposure impact on cardiac autonomic control before and following exercise

We aimed to investigate whether bright light (BL) exposure affects sympathovagal activity in controlling heart rate (HR) before and after exercise. Eighteen healthy men (28 ± 4 years) underwent two experimental conditions: one under BL (5000 lux) and another under dim light (DL < 8 lux). In both conditions, subjects performed an aerobic exercise bout (cycle ergometer, 30 min at 50-60% of HRreserve). HR (electrocardiography) and respiratory rate (piezoelectric belt) were initially assessed at baseline light (500 lux). Measurements were repeated before and 10 min after the exercise in both light conditions, BL and DL. Cardiac autonomic modulation was evaluated using spectral analysis of HR variability. Before exercise, DL did not change HR but decreased low- to high-frequency ratio of HR variability (LF/HF_RR, DL = -0.35 ± 0.43 vs. BL = +0.00 ± 0.55, p < 0.01). From pre- to post-exercise, HR increased similarly, while LF/HF_RR increase was greater in DL than BL (+1.12 ± 0.87 vs. +0.60 ± 0.98, p = 0.04). Contrary to our hypothesis, in healthy men, BL did not exacerbate HR and cardiac sympathovagal balance. However, DL exposure decreased pre-exercise cardiac sympathovagal balance, a difference that no longer persisted postexercise.