Photobiomodulation Effects on Fatigue and Muscle Damage Induced by NMES

Effects of Photobiomodulation on Fatigue and Muscle Damage Induced by Neuromuscular Electrical Stimulation in Healthy Individuals: a Randomized Clinical Trial

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.

Study Overview

• Status: Not yet recruiting
• Conditions: Fatigue; Electrical Stimulation; Muscle Damage; Discomfort; Photobiomodulation
• Intervention / Treatment: Device: Active Photobiomodulation; Other: NMES-evoked fatigue protocol; Device: Placebo Photobiomodulation

• Study Type: Interventional
• Enrollment (Estimated): 36
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Marco A Vaz, PhD; Phone Number: +555133085853; Email: marco.vaz@ufrgs.br

Study Locations

• Brazil
  • Rio Grande do Sul
    • Porto Alegre, Rio Grande do Sul, Brazil, 90690200
      • Laboratório de Pesquisa do Exercício
      • Contact: Jeam M Geremia, PhD; Phone Number: 5133085853; Email: jeam.geremia@ufrgs.br
      • Principal Investigator: Marco A Vaz, PhD
      • Sub-Investigator: Gustavo N Petter, MSc

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Healthy male and female volunteers.
• Age between 18 and 45 years.
• Practice physical activity regularly
• No history of musculoskeletal injuries in the lower limbs in the last 6 months
• Ability to tolerate NMES

Exclusion Criteria:

• Have sensory intolerable changes due to NMES
• Consumed coffee or another stimulant in the last 12 hours
• Have a body mass index (BMI) greater than 30 kg/m2 (grade I obesity)
• Present any contraindication for the performance of maximum effort
• Abnormal increase in blood pressure after maximal exertion

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Triple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Photobiomodulation (PBM); Participants in this arm will receive active photobiomodulation therapy.	Device: Active Photobiomodulation; 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.; Other: NMES-evoked fatigue protocol; 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).
Sham Comparator: Sham PBM; Participants in this arm will receive an inactive (placebo) photobiomodulation treatment.	Other: NMES-evoked fatigue protocol; 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).; Device: Placebo Photobiomodulation; 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.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Maximal voluntary isometric contraction (MVIC)	Largest knee extensor torque generated isometrically and voluntarily on an isokinetic dynamometer. Unit of Measure: Newton-meters (N.m)	Baseline (pre-intervention) on Day 1; immediately after the fatigue protocol on Day 1; and at 24, 48, and 72 hours after the fatigue protocol (on Days 2, 3, and 4, respectively).
Evoked fatigue	Fall in the evoked torque during the fatigue protocol. Unit of Measure: Newton-meters (N.m)	Continuously during the 20-minute fatigue protocol.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Muscle Echo Intensity	Quantitative analysis of muscle ultrasound images to assess changes in echo intensity, reflecting acute edema and changes in muscle quality. Analysis will be performed specifically on the Rectus Femoris (RF), Vastus Medialis (VM), and Vastus Lateralis (VL). Unit of Measure: Arbitrary Units (au) on a 0-255 grayscale	Baseline (pre-intervention) on Day 1; immediately after the fatigue protocol on Day 1; and at 24, 48, and 72 hours after the fatigue protocol (on Days 2, 3, and 4, respectively).
Pressure Pain Threshold	The minimum pressure at which a subject perceives a stimulus as painful, measured via pressure algometry on the quadriceps muscle bellies to quantify delayed onset muscle soreness (DOMS). Unit of Measure: Newtons (N)	Baseline (pre-intervention) on Day 1; immediately after the fatigue protocol on Day 1; and at 24, 48, and 72 hours after the fatigue protocol (on Days 2, 3, and 4, respectively).
Quadriceps Muscle Thickness	Ultrasound assessment of structural changes in the quadriceps muscle group, for the Rectus Femoris (RF), Vastus Medialis (VM), and Vastus Lateralis (VL). This variable evaluates acute morphological changes or edema-induced swelling following the NMES protocol. Unit of Measure: Millimeters (mm)	Baseline (pre-intervention) on Day 1; immediately after the fatigue protocol on Day 1; and at 24, 48, and 72 hours after the fatigue protocol (on Days 2, 3, and 4, respectively).
Countermovement Jump (CMJ) Height	Measure Description: Maximum jump height achieved during a vertical countermovement jump on a force platform to assess dynamic muscle power. Unit of Measure: Centimeters (cm)	Baseline (pre-intervention) on Day 1; immediately after the fatigue protocol on Day 1; and at 24, 48, and 72 hours after the fatigue protocol (on Days 2, 3, and 4, respectively).
Lower Limb Joint Kinematics During Jump	Measure Description: Sagittal plane kinematic analysis for the ankle, knee, hip, and trunk joints to evaluate movement strategies and joint range of motion during the countermovement jump. Unit of Measure: Degrees (°)	Baseline (pre-intervention) on Day 1; immediately after the fatigue protocol on Day 1; and at 24, 48, and 72 hours after the fatigue protocol (on Days 2, 3, and 4, respectively).
Force-Time Curve Dynamics During Jump	Analysis of the vertical ground reaction force-time curve during the propulsion phase of the countermovement jump. The primary parameter will be the Vertical Impulse, calculated as the integral of force over time. Unit of Measure: Newton-seconds (N.s)	Baseline (pre-intervention) on Day 1; immediately after the fatigue protocol on Day 1; and at 24, 48, and 72 hours after the fatigue protocol (on Days 2, 3, and 4, respectively).
Muscle Activation	Surface electromyography (sEMG) to assess muscle activation amplitude during MVIC. Unit of Measure: Microvolts (uV)	Baseline (pre-intervention) on Day 1; immediately after the fatigue protocol on Day 1; and at 24, 48, and 72 hours after the fatigue protocol (on Days 2, 3, and 4, respectively).
Vastus Lateralis Fascicle Length	Measure Description: Assessment of real-time changes in the fascicle length of the Vastus Lateralis muscle during the fatigue protocol using continuous ultrasound imaging. Unit of Measure: Millimeters (mm)	Continuously during the 20-minute fatigue protocol on Day 1.

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Vastus Lateralis Pennation Angle	Measure Description: Assessment of real-time changes in the pennation angle of the Vastus Lateralis muscle during the fatigue protocol using continuous ultrasound imaging. Unit of Measure: Degrees (°)	Continuously during the 20-minute fatigue protocol on Day 1.
Adipose Tissue Thickness	Measurement of the fat layer thickness overlying the Rectus Femoris, Vastus Medialis, and Vastus Lateralis using ultrasound imaging. This measure is used to characterize the sample's morphology and will serve as a covariate to adjust the delivered PBM dose and NMES current penetration analysis. Unit of Measure: Millimeters (mm)	Baseline

Collaborators and Investigators

• Sponsor: Federal University of Rio Grande do Sul
• Collaborators: Conselho Nacional de Desenvolvimento Científico e Tecnológico
• Investigators: Study Chair: Marco A Vaz, PhD, Federal University of Rio Grande do Sul; Study Director: Marco A Vaz, PhD, Federal University of Rio Grande do Sul; Principal Investigator: Marco A Vaz, PhD, Federal University of Rio Grande do Sul

Study record dates

Study Major Dates

• Study Start (Estimated): June 1, 2026
• Primary Completion (Estimated): August 30, 2026
• Study Completion (Estimated): September 30, 2026

Study Registration Dates

• First Submitted: April 27, 2026
• First Submitted That Met QC Criteria: May 15, 2026
• First Posted (Actual): May 22, 2026

Study Record Updates

• Last Update Posted (Actual): May 22, 2026
• Last Update Submitted That Met QC Criteria: May 15, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Fatigue; Electrical stimulation; Photobiomodulation; Discomfort; Muscle Damage
• Additional Relevant MeSH Terms: Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Fatigue
• Other Study ID Numbers: 5.309.992(1)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: A final decision regarding the sharing of individual participant data has not yet been made. The study team intends to evaluate this possibility following the primary data analysis, in accordance with institutional guidelines and ethical committee requirements.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No