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Effect of low-level laser (Ga-Al-As 655 nm) on skeletal muscle fatigue induced by electrical stimulation in rats

¹Department of Pharmacology, Laboratory of Biochemical Pharmacology of Free Radicals, Institute of Biomedical Sciences, University of São Paulo, São Paulo; ²Laboratory of Animal Experiments, IP&D UNIVAP, São José dos Campos; ³Centro de Ciências Biológicas e Saúde, Universidade Cruzeiro do Sul, São Paulo, Brazil; ⁴Department of Physiology, University of Bergen, Bergen; and ⁵Section of Physiotherapy Science, Institute of Public Health and Primary Health Care, University of Bergen, Bergen, Norway

Submitted 14 October 2005 ; accepted in final form 27 February 2006

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.

laser therapy; skeletal muscle; electrical stimulation; rats; fatigue

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