Effect of 655-nm low-level laser therapy on exercise-induced skeletal muscle fatigue in humans.
OBJECTIVE
To investigate if development of skeletal muscle fatigue during repeated voluntary biceps contractions could be attenuated by low-level laser therapy (LLLT).


BACKGROUND
Previous animal studies have indicated that LLLT can reduce oxidative stress and delay the onset of skeletal muscle fatigue.


METHODS
Twelve male professional volleyball players were entered into a randomized double-blind placebo-controlled trial, for two sessions (on day 1 and day 8) at a 1-wk interval, with both groups performing as many voluntary biceps contractions as possible, with a load of 75% of the maximal voluntary contraction force (MVC). At the second session on day 8, the groups were either given LLLT (655 nm) of 5 J at an energy density of 500 J/cm2 administered at each of four points along the middle of the biceps muscle belly, or placebo LLLT in the same manner immediately before the exercise session. The number of muscle contractions with 75% of MVC was counted by a blinded observer and blood lactate concentration was measured.


RESULTS
Compared to the first session (on day 1), the mean number of repetitions increased significantly by 8.5 repetitions (+/- 1.9) in the active LLLT group at the second session (on day 8), while in the placebo LLLT group the increase was only 2.7 repetitions (+/- 2.9) (p = 0.0001). At the second session, blood lactate levels increased from a pre-exercise mean of 2.4 mmol/L (+/- 0.5 mmol/L), to 3.6 mmol/L (+/- 0.5 mmol/L) in the placebo group, and to 3.8 mmol/L (+/- 0.4 mmol/L) in the active LLLT group after exercise, but this difference between groups was not statistically significant.


CONCLUSIONS
We conclude that LLLT appears to delay the onset of muscle fatigue and exhaustion by a local mechanism in spite of increased blood lactate levels.
Leal Junior
Ernesto Cesar Pinto
EC
Laboratory of Human Movement, University of Caxias do Sul, Caxias do Sul, RS, Brazil. ecplealj@ucs.br
Lopes-Martins
Rodrigo Alvaro Brandão
RA
Dalan
Francis
F
Ferrari
Maurício
M
Sbabo
Fernando Montanari
FM
Generosi
Rafael Abeche
RA
Baroni
Bruno Manfredini
BM
Penna
Sócrates Calvoso
SC
Iversen
Vegard V
VV
Bjordal
Jan Magnus
JM
D000328:Adult; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D006801:Humans; D028022:Low-Level Light Therapy; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000528:radiation effects*; D018482:Muscle, Skeletal / Q000528:radiation effects*