Effects of Acute Photobiomodulation on Heart Rate Variability in Physically Active Individuals: A Randomized and Controlled Clinical Trial.

Photobiomodulation (PBM) therapy is widely investigated for tissue recovery, performance enhancement, and post-exercise optimization. This study assessed whether PBM applied to the vagus nerve in the infra-auricular region, combined with resistance exercise, modulates cardiac autonomic function in healthy, physically active adults. In this acute randomized controlled trial, 34 volunteers were enrolled: 17 underwent PBM or sham PBM in a crossover design, while a control group (n = 17) received PBM without exercise. PBM was delivered with a total energy dose of 12 J. Heart rate variability (HRV) was analyzed in time, frequency, and non-linear domains. Results showed a slight reduction (p = 0.011) in approximate entropy (ApEn) in the PBM group compared with controls, but no significant differences were observed in other HRV indices. These findings suggest that PBM applied to the vagus nerve induces minimal acute modulation of autonomic complexity. Further studies with different dosimetries and exercise protocols are warranted.