Photobiomodulation on NMES-Induced Muscle Fatigue and Damage: A Pilot Study

Neuromuscular electrical stimulation (NMES) is an effective tool for muscle strengthening and rehabilitation, but its clinical application is often limited by rapid neuromuscular fatigue, muscle discomfort, and potential muscle damage. Photobiomodulation therapy (PBMT) using low-level lasers or LEDs has been proposed as an ergogenic and protective modality capable of attenuating exercise-induced muscle fatigue and damage. However, evidence regarding the acute preventive effects of PBMT on NMES-induced fatigue and muscle damage in humans remains limited and conflicting. The purpose of this randomized, sham-controlled, crossover pilot trial was to evaluate the acute effects of PBMT applied prior to an NMES-induced fatigue protocol on knee extensor neuromuscular fatigability, muscle damage, discomfort, and functional performance in healthy young individuals. Healthy participants had both lower limbs randomized to receive either active PBMT (810 nm, 240 J total per limb across 8 points) or sham PBMT 5 minutes prior to an NMES fatigue protocol (20 minutes of evoked isometric contractions at 20% of maximal voluntary contraction). Primary and secondary outcomes-including maximal voluntary isometric contraction (MVIC) torque, supramaximal twitch torque, muscle damage via ultrasound echointensity (rectus femoris and vastus lateralis), pain pressure thresholds (algometry), visual analog scale (VAS) for discomfort, and functional tests (Single Hop Test and stair ascent/descent)-were assessed at baseline, immediately post-fatigue, and at 24, 48, and 72 hours post-intervention.

Inclusion Criteria: * Healthy male and female adults aged between 18 and 40 years. * Engaging in regular physical activity (minimum of twice a week). * No history of hospitalization for COVID-19 in the past 12 months. * Demonstrated ability to tolerate neuromuscular electrical stimulation (NMES). * Capable of fully understanding and complying with the experimental protocol and procedures. Exclusion Criteria: * Presence of any sensory impairments or neurological alterations. * Ingestion of caffeine, coffee, energy drinks, or other stimulants in the 12 hours preceding the testing sessions. * Body Mass Index (BMI) greater than 30 kg/m². * Any medical contraindication to performing maximal physical exertion or presenting an abnormal cardiovascular/blood pressure response after maximal effort.