Tehran University of Medical Sciences Journal of Modern Rehabilitation 2538-385X 15 1 2020 12 23 7 14 Elham Gorji Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. Seyed Mohsen Mir Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. Siamak Bashardoust Tajali Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. Kazem Malmir Department of Physiotherapy, School of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran. 2020 09 08 2020 09 19 Introduction: The use of High Power Laser (HPL) has recently been emphasized in physiotherapy. Previous studies suggest that the prophylactic use of laser has ergogenic effects on athletic performance by increasing the contractile function of skeletal muscles. Recently, muscle function improvement is a new research idea in the field of laser therapy. Based on our knowledge, there are only two studies on the effects of HPL on muscle performance although with contradictory results. The purpose of this study was to investigate the effects of HPL on quadriceps muscle performance in male football players. Materials and Methods: Sixteen healthy male football players (Mean±SD age=18.53±7.2 years, Mean±SD body mass index=22.8±4.4 kg/m2) participated in a pretest-posttest study. The subjects received one session of HPL (808 nm, 80 j, 2 w) on quadriceps muscles. The Isometric Peak Torque (IPT), Single-Leg Hop Test (SLHT), and Y-balance Test (YBT) were measured at baseline and immediately after HPL. For statistical analysis, we used the paired sample t test. Results: Immediately after HPL, the IPT (P=0.001), SLHT (P=0.02), and YBT scores (P=0.001) significantly increased. Conclusion: The results of our study showed that immediate application of one session of HPL can improve IPT as well as functional tests. Although the sessions of laser application and assessment were limited and the sample size was small, it seems that HPL could improve muscle performance. Therefore, further research is warranted with large sample size and follow-up. https://jmr.tums.ac.ir/index.php/jmr/article/view/314