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

Effect of low-level laser (Ga-A1-As 655 nm) on skeletal muscle fatigue induced by electrical stimulation in rats. J Appl Physiol 101: 283-288, 2006. First published April 20, 2006; doi:10.1152/japplphysio1.01318.2005. -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/cm(2)) 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/cm(2) laser-irradiated group and the control group in mean T50% values. Laser-irradiated groups (0.5 and 1.0 J/cm(2)) 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/cm(2), 83.2% (SD 20.5) for 1.0 J/cm(2), 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/cm(2) 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/cm(2) LLLT groups had significantly lower creatine kinase levels than the 0.5 J/ cm(2) LLLT group and the control group. We conclude that LLLT doses of 0.5 and 1.0 J/ cm(2) can prevent development of muscular fatigue in rats during repeated tetanic contractions.