Evidence supports that low-level laser therapy (LLLT) minimizes fatigue effects on muscle performance. However, the ideal LLLT dosage to improve athletes? performance during sports activities, such as cycling, is still unclear. Therefore, the goal of this study was to investigate the effects of different LLLT dosages on cyclists? performance in time-to-exhaustion tests. In addition, we looked at the effects of LLLT on the frequency content of the EMG signals to assess fatigue mechanisms. Twenty male competitive cyclists participated in a crossover, randomized, double-blind and placebo-controlled trial. They performed an incremental cycling test to exhaustion (on day 1) followed by four time to exhaustion tests (on days 2 to 5) at their individual maximal power output (POMAX). Before each time-to-exhaustion test, different dosages of LLLT (135, 270 and 405 J/thigh, respectively) or placebo were applied at the quadriceps muscle bilaterally. Power output and muscle activation from both lower limbs were recorded throughout the tests. Increased performance in time-to-exhaustion tests was observed with the LLLT-135J (~22 s; p<0.01), LLLT-270J (~13 s; p=0.03) and LLLT-405J (~13 s; p=0.02) compared to placebo (149 ±23 s). Although LLLT-270J and LLLT-405J did not show significant differences in muscle activation compared to placebo, LLLT-135J led to an increased high-frequency content compared to placebo in both limbs at the end of the exhaustion test (p≤0.03). In conclusion, LLLT increased time-to-exhaustion in competitive cyclists, suggesting this intervention as a possible non-pharmacological ergogenic agent in cycling. Among the different dosages, LLLT-135J seems to promote the best effects.