Background: Photobiomodulation (PBM) using red light therapy (RLT), has attracted growing interest for its potential to support recovery, autonomic regulation, and energy metabolism. It may help the body function more efficiently and improve energy availability. However, existing studies remain limited and have mainly examined the combined effects of PBM on heart rate variability (HRV), substrate utilization, and blood pressure in relation to physical activity.

Aim: This pilot study examined the effects of red light exposure on heart rate variability, substrate utilization, and blood pressure in healthy men.

Method: This randomized crossover pilot study included six healthy male participants. Each participant received both active PBM and sham treatments in separate test sessions. Physiological measurements, including HRV, substrate utilization, total energy expenditure (TEE), and blood pressure, were assessed before, after, and during recovery following physical activity.

Results: No clear group-level effects of PBM on heart rate variability or blood pressure were observed. However, one participant showed a higher root mean square of successive differences and total power, along with a lower low-frequency/high-frequency ratio following PBM treatment, indicating improved autonomic recovery. Lower respiratory quotient values and higher total energy expenditure were also observed during recovery after physical activity following PBM treatment, suggesting a possible increase in fat oxidation and energy expenditure.

Conclusion: The results suggest that the physiological response to PBM may vary between individuals. Although the findings should be interpreted with caution given the small sample size, the study contributes to a better understanding of how red light-based PBM may influence recovery, autonomic regulation, and energy metabolism in relation to physical activity. Further studies with larger sample sizes are needed to clarify these effects.  

Keywords: autonomic nervous system, blood pressure, energy metabolism, heart rate variability, photobiomodulation, recovery, substrate utilization.