ORIGINAL ARTICLE Low-level laser therapy (LLLT) in human progressive-intensity running: effects on exercise performance, skeletal muscle status, and oxidative stress Thiago De Marchi & Ernesto Cesar Pinto Leal Junior & Celiana Bortoli & Shaiane Silva Tomazoni & Rodrigo Álvaro Brandão Lopes-Martins & Mirian Salvador Received: 10 January 2011 /Accepted: 4 May 2011 # Springer-Verlag London Ltd 2011 Abstract The aim of this work was to evaluate the effects of low-level laser therapy (LLLT) on exercise performance, oxidative stress, and muscle status in humans. A random- ized double-blind placebo-controlled crossover trial was performed with 22 untrained male volunteers. LLLT (810 nm, 200 mW, 30 J in each site, 30 s of irradiation in each site) using a multi-diode cluster (with five spots - 6 J from each spot) at 12 sites of each lower limb (six in quadriceps, four in hamstrings, and two in gastrocnemius) was performed 5 min before a standardized progressive- intensity running protocol on a motor-drive treadmill until exhaustion. We analyzed exercise performance (VO 2 max , time to exhaustion, aerobic threshold and anaerobic threshold), levels of oxidative damage to lipids and proteins, the activities of the antioxidant enzymes superox- ide dismutase (SOD) and catalase (CAT), and the markers of muscle damage creatine kinase (CK) and lactate dehydrogenase (LDH). Compared to placebo, active LLLT significantly increased exercise performance (VO 2 max p = 0.01; time to exhaustion, p =0.04) without changing the aerobic and anaerobic thresholds. LLLT also decreased post-exercise lipid (p =0.0001) and protein (p =0.0230) damages, as well as the activities of SOD (p =0.0034), CK (p =0.0001) and LDH (p =0.0001) enzymes. LLLT applica- tion was not able to modulate CAT activity. The use of LLLT before progressive-intensity running exercise increases exer- cise performance, decreases exercise-induced oxidative stress and muscle damage, suggesting that the modulation of the redox system by LLLT could be related to the delay in skeletal muscle fatigue observed after the use of LLLT. Keywords LLLT . Progressive-intensity exercise . Oxidative stress . Muscle damage Introduction The metabolism during contractile activity produces reactive oxygen species (ROS) [1], which can lead to muscle oxidative stress [2]. This can be one factor associated with a reduction in contractile function and muscle fatigue develops [3]. To counteract these effects, organisms present antioxidant defenses, such as the enzymes superoxide dismutase (SOD) and catalase (CAT), responsible for the dismutation of the superoxide (O2 •- ) radical and hydrogen peroxide (H 2 O 2 ), respectively [2]. Skeletal muscle fatigue is characterized by impairment of muscle ability to generate and maintain force production T. De Marchi : C. Bortoli : M. Salvador (*) Laboratory of Oxidative Stress and Antioxidants, Institute of Biotechnology, University of Caxias do Sul, Rua Francisco Getúlio Vargas, 1130, 950070–560, Caxias do Sul, RS, Brazil e-mail: msalvado@ucs.br T. De Marchi Sports Medicine Institute and Laboratory of Human Movement, University of Caxias do Sul, Caxias do Sul, RS, Brazil E. C. P. Leal Junior : R. Á. B. Lopes-Martins Post Graduate Program in Rehabilitation Sciences, Nove de Julho University (UNINOVE), São Paulo, SP, Brazil S. S. Tomazoni : R. Á. B. Lopes-Martins Laboratory of Pharmacology and Experimental Therapeutics, Institute of Biomedical Sciences (ICB), University of São Paulo, São Paulo, SP, Brazil Lasers Med Sci DOI 10.1007/s10103-011-0955-5