Photobiomodulation versus ischemic preconditioning for protection against exercise-induced muscle damage: protocol for a randomized controlled trial

Abstract Exercise-induced muscle damage (EIMD) occurs after unaccustomed eccentric exercise and may impair muscle recovery. Preconditioning with photobiomodulation (PBM) or ischemic preconditioning (IPC) may mitigate EIMD; however, no study has directly compared their effectiveness. This study aims to compare the effects of PBM and IPC applied prior to eccentric exercise on indirect markers of EIMD and associated perceptual responses. We hypothesized that MVIC trajectories would differ among the PBM, IPC, and sham groups, with PBM expected to provide greater preservation of MVIC than IPC. A prospective, randomized, placebo-controlled clinical trial with concealed allocation, blinded outcome assessors and statistician, and intention-to-treat analysis will be conducted. Healthy men (18–35 years) will be randomly allocated to PBM, IPC, or sham groups (n = 15 per group). After the intervention, participants will perform an eccentric exercise protocol for the elbow flexors consisting of 30 repetitions using a dumbbell load numerically matched to maximal voluntary isometric contraction (MVIC) values, with 45-second rest intervals. The primary outcome will be MVIC. Secondary outcomes include rate of force development, delayed-onset muscle soreness, pressure pain threshold, ultrasound echo intensity, range of motion, perceived exertion, and affective responses. Outcomes will be assessed at baseline, immediately after exercise (only MVIC), and at 24-, 48-, and 72-hours post-exercise. The primary analysis will assess the group × time interaction on MVIC using linear mixed-effects models, while secondary outcomes will be analyzed exploratorily. This study will provide, to our knowledge, the first direct comparison between PBM and IPC as preconditioning strategies to attenuate EIMD. The findings may help determine the most effective and clinically applicable intervention by considering both physiological and perceptual responses, thereby supporting decision-making in clinical and sports settings. Trial registration Brazilian Registry of Clinical Trials (REBEC), RBR-6gr5kf; registered February 19, 2020; amended August 26, 2026.