Photobiomodulation Effects on Fatigue and Muscle Damage Induced by NMES

Description

Neuromuscular electrical stimulation (NMES) is widely used to improve muscle strength and mitigate atrophy. However, its clinical efficacy is often limited by early neuromuscular fatigue, muscle damage, and discomfort, which reduce patient tolerance and contraction time. Photobiomodulation (PBM) has emerged as a potential therapy to enhance muscle performance and accelerate recovery by minimizing fatigue and damage. Despite its potential, few studies have investigated the effects of PBM applied specifically before an NMES-evoked fatigue protocol. This randomized, double-blind, placebo-controlled trial aims to evaluate the acute effects of PBM on neuromuscular fatigue, muscle damage, and functional outcomes in healthy young subjects. Participants will receive either active PBM (cluster probe: 5 lasers 810nm/200mW; 4 LEDs 660nm/10mW; Total Energy: 249.6 J per limb) or sham treatment 5 minutes before a fatiguing NMES protocol (80 contractions at 20% MVIC, 80 Hz, 1ms pulse width) applied to the quadriceps muscle. Assessments will be performed at baseline, immediately post-intervention, and at 24h, 48h, and 72h post-intervention. Primary outcomes include maximum and evoked isometric strength, mechanical work, and electrical muscle activity. Secondary outcomes include muscle damage (ultrasound echo-intensity), delayed onset muscle soreness (DOMS), functional performance (unilateral vertical jump), and clinical discomfort. The study seeks to determine if PBM can effectively modulate NMES-induced fatigue and muscle damage, potentially optimizing its clinical application.

Interventions

• Active Photobiomodulation (Device)
  Application of PBMT using a cluster probe (Thor-DD2; 5 laser diodes: 810nm, 200mW; 4 LEDs: 660nm, 10mW). The treatment involves 8 points on the quadriceps (2 on vastus medialis, 3 on vastus lateralis, and 3 on rectus femoris). Each point is irradiated for 30 seconds in continuous mode with direct contact and slight pressure. Total energy: 31.2 J per point and 249.6 J per limb. Both therapist and participant will wear protective goggles.
• Placebo Photobiomodulation (Device)
  The procedure is identical to the active PBMT (8 points, 30 seconds per point, same pressure and positioning), but the device will be turned off. To ensure blinding, participants will wear protective goggles and a blindfold to prevent visual perception of the light.
• NMES-evoked fatigue protocol (Other)
  Neuromuscular Electrical Stimulation (Myomed 932) applied to the quadriceps. Parameters: 80 Hz frequency, 1 ms pulse width (biphasic rectangular pulse), 5s:10s ON:OFF ratio with 1s ramp-up/down. The protocol lasts 20 minutes, totaling 80 evoked isometric contractions. Current intensity is adjusted to generate an initial torque of 20% of the baseline Maximum Voluntary Isometric Contraction (MVIC).

Eligibility criteria

Conditions

Locations

• Laboratório de Pesquisa do Exercício — Porto Alegre, Rio Grande do Sul, Brazil