Photobiomodulation Strengthens Muscles via Its Dual Functions in Gut Microbiota.

Photobiomodulation therapy (PBMT) alleviates fatigue and enhances mitochondrial bioenergetics, yet effects are modest when applied only to the thighs. Here, it is demonstrated that brief, non-invasive abdominal PBMT with 980 nm light (0.1 J cm-2) substantially improves endurance by preserving gut epithelial integrity and modulating microbiota. In graded treadmill protocols under anaerobic stress, combined abdomen-and-legs PBMT nearly doubles time to exhaustion versus sham by day 20 (70.23 vs 32.38 min; P < 0.0001) and remains superior at day 30 (55.56 vs 32.38 min; P < 0.0001). PBMT preserves mitochondrial cristae and mass in gastrocnemius and soleus muscles (P ≤ 0.0018), achieving a fourfold increase over sham (P < 0.0001). Abdominal PBMT maintains seven major gut phyla disrupted by intense exercise, enriches SCFA-producing taxa, reduces pathobionts, and elevates circulating and fecal butyrate, spermidine, L-carnitine, and acetylL-carnitine (all P ≤ 0.0001). Ex vivo assays under anaerobic, acidic conditions confirm PBMT-driven expansion of key anaerobes (P < 0.05-0.0001). In a lactic-acidosis model, abdominal PBMT reduces peak weight loss (≈5% vs ≈10%) and accelerates recovery. These findings establish abdominal PBMT as a non-invasive modality that reverses epithelial injury and dysbiosis, revealing translational potential for enhancing performance, rehabilitation, and managing disorders associated with dysbiosis or mitochondrial dysfunction.