The optimal time-response window for photobiomodulation therapy (PBMT) using low-level laser therapy (LLLT) and/or light emitting diodes therapy (LEDT) before physical activity still wasn't fully investigated. The aim of the present study will be to investigate the better of four time-response windows for PBMT use before exercise in humans. For such, a preliminary study will be carried out with 20 healthy and untrained volunteers to determine if there is a difference between the measurement of creatine kinase (CK) activity when samples were obtained by puncture of the antecubital vein or by microdialysis near to the vastus lateralis muscle, using an eccentric exercise protocol in an isokinetic dynamometer. Posteriorly, a randomized, triple-blinded, placebo-controlled trial will be performed. Fifty healthy untrained male subjects will be randomly allocated to five experimental groups: Placebo, PBMT 5 mins, PBMT 3h, PBMT 6h and PBMT 1 day. PBMT will be applied precisely two minutes after baseline maximum voluntary contraction (MVC) test. Then, after five minutes, 3, 6 hours or 1 day (24 hours) of PBMT the eccentric exercise protocol will be performed. It will be analyzed maximum voluntary contraction (MVC), creatine kinase (CK) activity through the method determined from the preliminary study, and delayed onset muscle soreness (DOMS). Assessments will be performed at baseline, immediately after, 1, 24 and 48 hours after the eccentric exercise protocol.
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