A single photobiomodulation session selectively improves vocal stability and respiratory capacity in teachers with severe vocal fatigue.

Vocal fatigue (VF) is a significant occupational burden for professional voice users, such as teachers, for whom rapid and effective interventions remain limited. Photobiomodulation (PBM), a noninvasive therapy that uses low-intensity light to mitigate inflammation and promote tissue repair, is a promising therapeutic strategy. In this study, we investigated the immediate effects of a single PBM session on key acoustic and respiratory parameters in female teachers with VF. In this single-arm, pre-post clinical trial, we enrolled 41 female primary school teachers (age range: 28-40 years) with symptoms of vocal fatigue classified as mild (n = 19), moderate (n = 18), or severe (n = 4). A single 5-minute PBM session was administered to the laryngeal region using a light-emitting diode (LED) device delivering 1 W of optical power across two wavelengths (640 and 940 nm). Acoustic parameters (jitter, shimmer, and connected speech frequency) and respiratory capacity were measured before and immediately after the intervention. In the severe subgroup, jitter decreased (p = 0.005) and mean autocorrelation increased (p = 0.024), while connected speech (p = 0.056) and respiratory capacity (p = 0.058) showed trends toward improvement. In the moderate subgroup, peak flow increased (p = 0.002). No meaningful changes were observed in the mild subgroup. A single session of photobiomodulation therapy resulted in immediate and significant improvements in vocal quality and respiratory function, particularly in teachers with severe vocal fatigue. These findings position PBM as a promising non-invasive tool for rapid vocal rehabilitation in individuals with pronounced phonatory deficits. However, these findings should be interpreted in consideration of several limitations, including the small sample size, particularly in the severe subgroup, the absence of a control group, and the short, immediate follow-up period. The uneven distribution of participants across severity levels may also limit generalizability. Despite these constraints, the pronounced improvement observed in the severe vocal-fatigue subgroup underscores the clinical relevance of PBM as a rapid, non-invasive option for individuals with substantial phonatory impairment.