Photobiomodulation Does Not Increase Mitochondrial Respiration in Skeletal Muscle or Skin Tissue in Humans

PURPOSE: Low-level laser therapy, also referred to as photobiomodulation (PBM), is rapidly gaining popularity as a non-invasive treatment for various conditions and as a means to enhance health and performance. PBM has been proposed to directly increase mitochondrial activity in skin and skeletal muscle and activate various molecular signalling pathways. However, evidence for the proposed properties of PBM in vivo in humans is lacking. METHODS: In a within-participant study design, 12 healthy men and women (6/6 m/f; age: 25±6 y; BMI: 23.3±2.2kg/m2) received PBM on a randomized leg, while the other leg received sham-treatment (no light emitted, CON). Three cycles of PBM or sham-treatment were performed for 5 min 16 sec each (5.6 kJ light energy/cycle for PBM). Skin temperature was measured before and after treatment. After treatment, skin and muscle samples were collected from both legs. Mitochondrial respiration was measured in permeabilized muscle fibers and minced skin tissue using an Oroboros Oxygraph-O2k. Muscle metabolic gene expression was assessed using custom made microfluidic cards. RESULTS: Skin temperature increased only in the PBM treated leg (+8.0±1.4 °C; P<0.001). No differences were observed between the PBM and CON treated legs in maximal complex I+II-linked respiration in skin (2.7±0.8 vs 2.6±0.7 pmol/sec/mg wet weight, respectively; P=0.66) or muscle (474±114 vs 467±81 pmol/sec/mg dry weight, respectively; P=0.71). Furthermore, no differences were observed in muscle mitochondrial ADP sensitivity (apparent ADP half-time: 1310±180 vs 1229±240 µM ADP, respectively; P=0.14). Of the 91 genes, expression between legs differed for 3 genes only. CONCLUSIONS: A single session of photobiomodulation does not increase mitochondrial respiration in skin or underlying muscle tissue and does not modulate muscle gene expression ex vivo in humans.