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

## TL;DR

This study tested if light therapy on the vagus nerve affects heart function in active individuals during exercise, finding only a small change in heart rate variability.

## Contribution

This is the first study to investigate PBM on the vagus nerve in combination with exercise in healthy individuals.

## Key findings

- PBM caused a slight reduction in approximate entropy (ApEn) compared to controls.
- No significant differences were observed in other heart rate variability indices.
- PBM may minimally affect autonomic complexity, but more research is needed.

## Abstract

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.

This article is the first to approach the use of light acting on the vagus nerve in individuals undergoing physical exercise. Although we only obtained one isolated parameter as a difference in HRV, it is a first indication that we may be able to intervene in this vagal control process over the heart with PBM. Future perspectives are shown for new clinical trials with different doses and wavelengths to analyze the possibility of more robust effects.