title: Effect of low-level laser (Ga-Al-As 655 nm) on skeletal muscle fatigue induced by electrical stimulation in rats.
abstract: We investigated whether low-level laser therapy (LLLT) can reduce muscular fatigue during tetanic contractions in rats. Thirty-two male Wistar rats were divided into four groups receiving either one of three different LLLT doses (0.5, 1.0, and 2.5 J/cm2) or a no-treatment control group. Electrical stimulation was used to induce six tetanic muscle contractions in the tibial anterior muscle. Contractions were stopped when the muscle force fell to 50% of the initial value for each contraction (T50%). There was no significant difference between the 2.5 J/cm2 laser-irradiated group and the control group in mean T50% values. Laser-irradiated groups (0.5 and 1.0 J/cm2) had significantly longer T50% values than the control group. The relative peak force for the sixth contraction in the laser-irradiated groups were significantly higher at 92.2% (SD 12.6) for 0.5 J/cm2, 83.2% (SD 20.5) for 1.0 J/cm2, and 82.9% (SD 18.3) for 2.5 J/cm2 than for the control group [50% (SD 15)]. Laser groups receiving 0.5 and 1.0 J/cm2 showed significant increases in mean performed work compared with both the control group and their first contraction values. Muscle damage was indirectly measured by creatine kinase levels in plasma. A distinct dose-response pattern was found in which 1.0 and 2.5 J/cm2 LLLT groups had significantly lower creatine kinase levels than the 0.5 J/cm2 LLLT group and the control group. We conclude that LLLT doses of 0.5 and 1.0 J/cm2 can prevent development of muscular fatigue in rats during repeated tetanic contractions.
authors.affiliation: Department of Pharmacology, Laboratory of Biochemical Pharmacology of Free Radicals, Institute of Biomedical Sciences, University of São Paulo, Brazil. rmartins@icb.usp.br
authors.forename: Rodrigo Alvaro B
authors.initials: RA
authors.lastname: Lopes-Martins
authors.forename: Rodrigo Labat
authors.initials: RL
authors.lastname: Marcos
authors.forename: Patrícia Sardinha
authors.initials: PS
authors.lastname: Leonardo
authors.forename: Antônio Carlos
authors.initials: AC
authors.lastname: Prianti
authors.forename: Marcelo Nicolas
authors.initials: MN
authors.lastname: Muscará
authors.forename: Flavio
authors.initials: F
authors.lastname: Aimbire
authors.forename: Lúcio
authors.initials: L
authors.lastname: Frigo
authors.forename: Vegard V
authors.initials: VV
authors.lastname: Iversen
authors.forename: Jan Magnus
authors.initials: JM
authors.lastname: Bjordal
mesh_terms: D000818:Animals; D003402:Creatine Kinase / Q000097:blood; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation; D000860:Hypoxia / Q000503:physiopathology / Q000517:prevention & control; D028022:Low-Level Light Therapy; D008297:Male; D009119:Muscle Contraction / Q000502:physiology* / Q000528:radiation effects; D018763:Muscle Fatigue / Q000502:physiology* / Q000528:radiation effects*; D018482:Muscle, Skeletal / Q000201:enzymology / Q000294:innervation / Q000503:physiopathology* / Q000528:radiation effects; D051381:Rats; D017208:Rats, Wistar
chemical_list: D003402:Creatine Kinase