Acute Effects of High-Intensity Laser Therapy on Pain, Muscle Stiffness, and Grip Strength in Healthy Adults (HILT)

The goal of this clinical trial is to learn whether high-intensity laser therapy applied before exercise reduces the loss of handgrip strength, muscle stiffness, and pain after a tiring forearm exercise in healthy adults. This therapy delivers laser light through the skin to the underlying tissues.

The main questions this study aims to answer are:

Does laser therapy reduce the loss of handgrip strength after exercise compared with placebo treatment?

Does laser therapy reduce the increase in forearm muscle stiffness after exercise?

Does laser therapy reduce pain after exercise?

Researchers will compare active laser therapy with placebo laser treatment to assess whether the active treatment affects the muscles' response to exercise. Each participant will receive both treatments on separate visits. The order of treatments will be assigned by chance.

Participants will attend two laboratory visits at the Faculty of Health Sciences, University of Primorska, Slovenia. At one visit, they will receive active laser therapy over the muscles that bend the wrist in their dominant forearm. At the other visit, they will receive placebo treatment over the same area.

At each visit, participants will:

Rest before the initial measurements.

Have their handgrip strength, forearm muscle stiffness, and pain measured before treatment.

Receive active laser therapy or placebo treatment.

Wait five minutes before starting the exercise procedure.

Complete a wrist-strength test, then hold a muscle contraction at half of their maximum wrist-bending strength until they can no longer maintain the required force.

Have their handgrip strength, muscle stiffness, and pain measured again immediately after exercise and five and fifteen minutes later.

Handgrip strength will be measured by squeezing a handheld device. Muscle stiffness will be measured using a device that applies a brief, gentle mechanical tap to the skin over the muscle. Participants will rate their pain using a visual scale.

Participants will be asked to avoid strenuous physical activity for at least 24 hours before each visit and to keep their diet and regular supplement use similar before both visits.

The main outcome is the change in handgrip strength from before treatment to after exercise. Changes in muscle stiffness and pain will also be compared between the two treatments. Researchers expect active laser therapy to result in a smaller decrease in handgrip strength and smaller increases in muscle stiffness and pain than placebo treatment.

Study Overview

• Status: Not yet recruiting
• Conditions: Healthy Adult; Health Adult Subjects; Fatigue Recovery; Exercise-Induced Muscle Fatigue
• Intervention / Treatment: Device: High-Intensity Laser Therapy (HILT) and sham HILT

• Study Type: Interventional
• Enrollment (Estimated): 30
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Denisa Manojlović Ivezić, PhD; Phone Number: +385989394672; Email: denisa.manojlovic@fvz.upr.si

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 40 years (Adult)
• Accepts Healthy Volunteers: Yes
• Genders Eligible for Study: All

Description

Inclusion Criteria:

• Healthy adults aged 18 to 40 years.
• Willingness to participate and provide written informed consent.

Exclusion Criteria:

• Acute or chronic injuries of the upper limbs.
• Neurological, musculoskeletal, or systemic diseases that could affect muscle function.
• Contraindications to high-intensity laser therapy.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Prevention
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Active HILT Followed by Placebo HILT; High-intensity laser therapy will be administered using the Platinum 4 device (Summus Medical Laser) over the wrist flexor muscles of the dominant forearm, from the medial epicondyle of the humerus toward the wrist. All four wavelengths available on the device will be used. Each participant will receive one active treatment session, followed by a five-minute interval before the muscle-fatiguing exercise procedure. Both the participant and the therapist will wear appropriate protective eyewear.	Device: High-Intensity Laser Therapy (HILT) and sham HILT; High-intensity laser therapy will be administered using the Platinum 4 device (Summus Medical Laser) over the wrist flexor muscles of the dominant forearm, from the medial epicondyle of the humerus toward the wrist. All four wavelengths available on the device will be used. Each participant will receive one active treatment session, followed by a five-minute interval before the muscle-fatiguing exercise procedure. Both the participant and the therapist will wear appropriate protective eyewear. Placebo high-intensity laser therapy will be administered over the wrist flexor muscles of the dominant forearm before the same muscle-fatiguing exercise procedure used in the active treatment condition. Each participant will receive one placebo treatment session, followed by a five-minute interval before the exercise procedure.
Sham Comparator: Sham HILT Followed by Placebo HILT; Sham high-intensity laser therapy will be administered over the wrist flexor muscles of the dominant forearm before the same muscle-fatiguing exercise procedure used in the active treatment condition. Each participant will receive one placebo treatment session, followed by a five-minute interval before the exercise procedure.	Device: High-Intensity Laser Therapy (HILT) and sham HILT; High-intensity laser therapy will be administered using the Platinum 4 device (Summus Medical Laser) over the wrist flexor muscles of the dominant forearm, from the medial epicondyle of the humerus toward the wrist. All four wavelengths available on the device will be used. Each participant will receive one active treatment session, followed by a five-minute interval before the muscle-fatiguing exercise procedure. Both the participant and the therapist will wear appropriate protective eyewear. Placebo high-intensity laser therapy will be administered over the wrist flexor muscles of the dominant forearm before the same muscle-fatiguing exercise procedure used in the active treatment condition. Each participant will receive one placebo treatment session, followed by a five-minute interval before the exercise procedure.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Handgrip Strength	Handgrip strength will be measured using a Baseline Lite handheld dynamometer on the dominant hand. Participants will be seated with the upper arm alongside the trunk, the elbow flexed to 90 degrees, the forearm in a neutral position, and the wrist in slight extension and ulnar deviation. Three maximal grip attempts will be performed at each assessment, and the highest value will be used for analysis. Changes from the pre-intervention baseline will be compared between active and placebo high-intensity laser therapy.	At each of the two study visits: before the intervention (baseline), immediately after the fatiguing exercise, and 5 and 15 minutes after the fatiguing exercise. Visits will be separated by at least one week.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Wrist Flexor Muscle Stiffness	Muscle stiffness will be assessed using the MyotonPRO device at a predefined and marked anatomical measurement site over the wrist flexor muscles of the dominant forearm. The device applies a brief mechanical impulse to the skin and measures the tissue response to calculate muscle stiffness in newtons per meter (N/m). Higher values indicate greater stiffness. Changes from the pre-intervention baseline will be compared between active and placebo high-intensity laser therapy.	At each of the two study visits: before the intervention (baseline), immediately after the fatiguing exercise, and 5 and 15 minutes after the fatiguing exercise. Visits will be separated by at least one week.

Collaborators and Investigators

• Sponsor: University of Primorska

Study record dates

Study Major Dates

• Study Start (Estimated): December 1, 2026
• Primary Completion (Estimated): February 1, 2027
• Study Completion (Estimated): March 1, 2027

Study Registration Dates

• First Submitted: October 19, 2026
• First Submitted That Met QC Criteria: October 19, 2026
• First Posted (Actual): October 26, 2026

Study Record Updates

• Last Update Posted (Actual): November 5, 2026
• Last Update Submitted That Met QC Criteria: November 2, 2026
• Last Verified: August 1, 2026

More Information

Terms related to this study

• Other Study ID Numbers: HILT effects_forearm

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

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