Photobiomodulation on NMES-Induced Muscle Fatigue and Damage

Effects of Photobiomodulation and Stimulation Sites on Muscle Fatigue and Damage Induced by Neuromuscular Electrical Stimulation in Healthy Individuals

Neuromuscular electrical stimulation (NMES) is effective for strength training and rehabilitation, but non-selective motor unit recruitment often induces rapid fatigue, discomfort, and muscle damage. Photobiomodulation therapy (PBMT) has been proposed to attenuate muscle fatigue and accelerate recovery, yet evidence regarding its acute prophylactic effects against NMES-induced fatigue remains limited. This randomized, single-blind, sham-controlled crossover pilot trial evaluates the acute effects of pre-exercise PBMT on knee extensor neuromuscular fatigability, muscle damage, discomfort, and functional recovery following a standardized NMES fatigue protocol in healthy adults.

Study Overview

• Status: Completed
• Conditions: Muscle Damage; Neuromuscular Electrical Stimulation (NMES); Delayed Onset Muscle Soreness (DOMS); Muscle Fatigue (C23.888.592.612.612); Photobiomodulation (PBM)
• Intervention / Treatment: Device: Photobiomodulation Therapy (PBMT); Device: Sham Photobiomodulation

Detailed Description

This study utilizes a randomized, single-blind, sham-controlled crossover design to evaluate the acute effects of photobiomodulation therapy (PBMT) on neuromuscular electrical stimulation (NMES)-induced fatigue in healthy individuals.

Participants undergo testing across two intervention blocks separated by a 7-day washout period between limbs:

Intervention Phase: Five minutes prior to an electrically evoked fatigue protocol, participants receive either active PBMT (multi-diode GaAlAs laser cluster; 810 nm; 200 mW per diode; 30 J per point across 8 quadriceps sites; total energy dose: 240 J) or sham PBMT (identical positioning with the device inactive and acoustic blinding).

NMES Fatigue Protocol: The protocol is performed on an isokinetic dynamometer with the knee fixed at 90° flexion. Rectangular biphasic symmetrical pulses (100 Hz; 1 ms pulse width; 5 s on, 10 s off) are delivered over 20 minutes to evoke 60 isometric contractions adjusted to an initial torque of 20% maximal voluntary isometric contraction (MVIC).

Evaluation Timeline: Neuromuscular and functional assessments are conducted at Baseline, Immediately Post-Fatigue, and at 24, 48, and 72 hours post-protocol. Tests include maximal voluntary isometric torque, resting supramaximal evoked twitches, transverse ultrasound echointensity of the rectus femoris and vastus lateralis, pressure pain thresholds via algometry, Visual Analog Scales for discomfort, and horizontal Single Hop Test performance.

• Study Type: Interventional
• Enrollment (Actual): 12
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Brazil
  • Rio Grande do Sul
    • Porto Alegre, Rio Grande do Sul, Brazil, 90690200
      • Laboratório de Pesquisa do Exercício

Participation Criteria

Eligibility Criteria

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

Description

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.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Active PBMT + NMES; Participants receive active Photobiomodulation Therapy (PBMT) applied to the knee extensor muscles 5 minutes prior to undergoing a 20-minute neuromuscular electrical stimulation (NMES) fatigue protocol on the randomized lower limb.	Device: Photobiomodulation Therapy (PBMT); Multi-diode cluster probe (GaAlAs laser; 5 diodes; wavelength: 810 nm; power output: 200 mW per diode; continuous mode) applied across 8 points over the quadriceps femoris (3 on rectus femoris, 3 on vastus lateralis, and 2 on vastus medialis) for 30 seconds per point (30 J/point), delivering a total energy dose of 240 J per limb.
Sham Comparator: Sham PBMT + NMES; Participants receive sham Photobiomodulation Therapy (device turned off, identical positioning and acoustic blinding) applied to the knee extensor muscles 5 minutes prior to undergoing a 20-minute neuromuscular electrical stimulation (NMES) fatigue protocol on the contralateral lower limb.	Device: Sham Photobiomodulation; Identical probe positioning over the 8 quadriceps locations for 30 seconds per point with the laser device completely turned off. Auditory headphones are used to blind participants against sound cues.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Maximal Voluntary Isometric Contraction (MVIC) Torque	Knee extensor peak isometric torque measured on an isokinetic dynamometer (Biodex System 3 Pro) during 5-second maximal isometric contractions with the knee fixed at 90° flexion, expressed in Newton-meters (N.m).	Baseline, Immediately post-fatigue protocol, 24 hours, 48 hours, and 72 hours post-fatigue.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Muscle Damage via Ultrasound Echointensity	Quantitative grayscale histogram analysis (0 = black, 255 = white) of transverse ultrasound images (ImageJ software) of the rectus femoris (at 40%, 50%, and 60% of the femur length) and vastus lateralis (at 50% of the femur length) muscles to assess structural muscle damage.	Baseline, Immediately post-fatigue protocol, 24 hours, 48 hours, and 72 hours post-fatigue.
Supramaximal Evoked Twitch Torque	Knee extensor evoked torque produced by single supramaximal electrical twitches (1 Hz, 500 µs rectangular biphasic pulses at rest) delivered to the rectus femoris motor point, measured in Newton-meters (N.m) on the isokinetic dynamometer to evaluate peripheral muscle fatigue.	Baseline, Immediately post-fatigue protocol, 24 hours, 48 hours, and 72 hours post-fatigue.
Evoked Neuromuscular Efficiency	Ratio between the supramaximal evoked twitch peak torque and the applied current intensity (Nm/mA) during resting single pulses.	Baseline, Immediately post-fatigue protocol, 24 hours, 48 hours, and 72 hours post-fatigue.
Sitting Muscle Discomfort	Subjective sensation of discomfort/pain in the quadriceps femoris evaluated while seated at rest using a 10 cm Visual Analog Scale (VAS), where 0 cm represents 'no discomfort' and 10 cm represents 'maximum discomfort'.	Baseline, Immediately post-fatigue protocol, 24 hours, 48 hours, and 72 hours post-fatigue.
Pain Pressure Threshold (PPT)	Mechanical pain sensitivity measured using a digital pressure algometer (applied at 90° in kgf/cm²) over the rectus femoris, vastus lateralis, and vastus medialis muscle bellies to identify delayed onset muscle soreness.	Baseline, Immediately post-fatigue protocol, 24 hours, 48 hours, and 72 hours post-fatigue.
Single Hop Test (SHT) Functional Performance	Maximal horizontal single-leg hop distance normalized to limb length, calculated as: [Hop Distance (cm) / Limb Length (cm)] * 100.	Baseline, Immediately post-fatigue protocol, 24 hours, 48 hours, and 72 hours post-fatigue.
Discomfort During Stair Ascent and Descent	Level of discomfort reported on a 10 cm Visual Analog Scale (VAS) immediately after ascending and descending a 10-step staircase.	Baseline, Immediately post-fatigue protocol, 24 hours, 48 hours, and 72 hours post-fatigue.
Total Mechanical Work During Fatigue Protocol	Cumulative mechanical work quantified by the sum of the torque-time integral (TTI) across all 60 evoked contractions during the 20-minute NMES protocol (expressed in N.m.s).	During the 20-minute NMES fatigue protocol.
Fatigue Index (% Work Decline)	Percentage reduction in work performed between the first 5 evoked contractions and the last 5 evoked contractions of the NMES fatigue protocol, calculated as: [(Initial Work - Final Work) / Initial Work] * 100.	During the 20-minute NMES fatigue protocol.

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; Principal Investigator: Marco A Vaz, PhD, Federal University of Rio Grande do Sul

Study record dates

Study Major Dates

• Study Start (Actual): November 1, 2022
• Primary Completion (Actual): August 1, 2023
• Study Completion (Actual): December 1, 2023

Study Registration Dates

• First Submitted: August 24, 2026
• First Submitted That Met QC Criteria: August 24, 2026
• First Posted (Actual): August 27, 2026

Study Record Updates

• Last Update Posted (Actual): August 31, 2026
• Last Update Submitted That Met QC Criteria: August 26, 2026
• Last Verified: August 1, 2026

More Information

Terms related to this study

• Keywords: Neuromuscular Electrical Stimulation; Photobiomodulation; Pilot Study; Muscle Fatigue; Low-Level Laser Therapy
• Additional Relevant MeSH Terms: Therapeutics; Laser Therapy; Phototherapy; Low-Level Light Therapy
• Other Study ID Numbers: 56181622.4.0000.5347

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED
• IPD Plan Description: Individual participant data will not be publicly shared to protect participant confidentiality in accordance with the local ethics committee approval.

Drug and device information, study documents

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