Effects of Carnitine Supplementation on Exercise-Induced Muscle Damage: A Randomized Controlled Trial

INVESTIGATION OF THE EFFECT OF L-CARNITINE SUPPLEMENTS IN ATHLETES ON MUSCLE DAMAGE AND DELAYED ONSET MUSCLE PAIN (DOMS) AFTER HIGH INTENSITY INTERVAL TRAINING

This clinical study aims to investigate the effects of L-carnitine supplementation on recovery following high-intensity interval exercise in young athletes. L-carnitine plays an important role in energy metabolism by facilitating the transport of long-chain fatty acids into the mitochondria for oxidation. It has been suggested that L-carnitine supplementation may contribute to improved exercise performance and recovery by reducing metabolic stress and muscle damage associated with high-intensity exercise.

The primary objective of this study is to determine whether L-carnitine supplementation can attenuate exercise-induced muscle damage and delayed onset muscle soreness (DOMS) following high-intensity exercise. In addition, the study aims to evaluate the potential effects of L-carnitine on peak blood lactate concentration, as well as performance-related parameters including maximal power output, relative maximal power output, mean power output, and relative mean power output during high-intensity exercise.

To address these objectives, participants will be randomly assigned to receive either L-carnitine supplementation or a placebo for a period of 21 days. The placebo will consist of an inert substance designed to resemble the supplement but without any active ingredient. The effects of supplementation on performance and recovery outcomes will be evaluated following a standardized high-intensity exercise protocol.

Participants will be instructed to take the assigned supplement daily throughout the supplementation period. Communication and compliance monitoring will be conducted through a WhatsApp group established by the research team, which will be used to provide reminders and ensure adherence to the study protocol.

To minimize potential confounding factors related to pre-existing muscle damage, participants will be instructed to avoid unfamiliar or strenuous physical activity, particularly resistance exercises involving eccentric contractions, for one week prior to the experimental protocol. Additionally, during the supplementation period, participants will be asked to refrain from consuming foods rich in carnitine, such as meat and dairy products, in order to control dietary carnitine intake.

The findings of this study are expected to provide further insight into the potential role of L-carnitine supplementation in enhancing exercise performance and promoting recovery following high-intensity exercise in young athletes.

Study Overview

• Status: Completed
• Conditions: Exercise Ergogenics; Recovery Methods; Carnitine Ingestion; Exercise Fatigue; Exercise and Recovery
• Intervention / Treatment: Dietary supplement: L-Carnitine; Other: Placebo

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

Contacts and Locations

Study Locations

• Turkey (Türkiye)
  • Küçükçekmece
    • Istanbul, Küçükçekmece, Turkey (Türkiye), 34303
      • Istanbul Sabahattin Zaim University, Faculty of Sports Sciences

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Male athletes aged 18-25 years
• Regularly participating in organized sports training for at least 3 days per week
• Healthy individuals with no diagnosed cardiovascular, metabolic, or musculoskeletal disorders
• Willingness to comply with the supplementation protocol for 21 days
• Agreement to refrain from consuming foods rich in carnitine (e.g., meat and dairy products) during the supplementation period
• Agreement to avoid unfamiliar or strenuous exercise, particularly resistance exercise involving eccentric contractions, for one week prior to the experimental protocol
• Provision of written informed consent to participate in the study

Exclusion Criteria:

• Use of dietary supplements (including L-carnitine) within the last 3 weeks
• Presence of musculoskeletal injury or chronic disease that may affect exercise performance
• Use of medications that may influence muscle metabolism or recovery
• Known allergy or intolerance to the supplement components
• Failure to comply with the dietary or supplementation protocol
• Participation in another clinical or exercise intervention study during the study period
• Any condition deemed unsuitable for participation by the research team

Study Plan

How is the study designed?

Design Details

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

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: L-Carnitine Supplementation Group; Participants in this group will receive L-carnitine supplementation for 21 days prior to completing a standardized high-intensity interval exercise protocol. The effects of supplementation on exercise-induced muscle damage, recovery, blood lactate levels, and anaerobic performance will be evaluated.	Dietary supplement: L-Carnitine; Although the optimal dose and method of L-Carnitine use are not clearly defined in the literature, it has been reported that daily doses of 2-4 g are relatively ineffective in raising plasma levels unless used due to bioavailability. On the other hand, it has been suggested that the absolute bioavailability of oral doses greater than 1 g is less than 20% due to low gastrointestinal membrane permeability and limited capacity of intestinal transporters. However, pharmacokinetic data support the administration of L-Carnitine in several doses per day. Therefore, while the literature shows varying doses ranging from 1-4 g/day, generally in single daily doses, in this study, L-Carnitine participants will be given 3 g (3 g/d) of L-Carnitine daily for 3 weeks, at 1 g (1 g/8h) every 8 hours.; Other Names: Participants will consume 3 g/day of L-carnitine for 21 days.
Placebo Comparator: Placebo Group; Participants in this group will receive a placebo supplement identical in appearance to the L-carnitine supplement for 21 days prior to the high-intensity interval exercise protocol.	Other: Placebo; In this study, placebo group participants will be given 3 grams (3g/d) of powdered sugar daily (1g/8h) at 8-hour intervals for 3 weeks, which resembles L-Carnitine supplements in shape and color.; Other Names: Placebo participants will be given 3g/d of L-carnitine-like powdered sugar for 21 days.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Exercise-Induced Muscle Damage (Creatine Kinase and LDH)	Exercise-induced muscle damage will be assessed using blood biomarkers, including creatine kinase (CK) and lactate dehydrogenase (LDH) concentrations measured after the high-intensity interval exercise protocol.	Immediately before starting a 21-day L-Carnitine supplement, Immediately after 21 days of L-Carnitine supplementation and 2 hours, 24 hours, 48 hours, and 72 hours after the exercise protocol.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Delayed Onset Muscle Soreness (DOMS)	Perceived muscle soreness will be evaluated using a visual analog scale (VAS) to assess delayed onset muscle soreness following the high-intensity exercise protocol.	Immediately after exercise and 2 hours, 24 hours, 48 hours, and 72 hours post-exercise
Peak Blood Lactate Concentration	Peak blood lactate concentration will be measured to evaluate the metabolic response to the high-intensity exercise protocol.	Immediately before the exercise test, and at 1, 3, 5, 7, 9, and 11 minutes after the exercise test ends.
Maximal Power Output	Maximal power output during the high-intensity exercise protocol will be recorded to evaluate anaerobic performance.	The 4*30 second exercise protocol: immediately after the first 30 seconds, immediately after the second 30 seconds, immediately after the third 30 seconds, immediately after the fourth 30 seconds.
Relative Maximal Power Output	Relative maximal power output (power normalized to body mass) will be assessed to evaluate anaerobic performance.	The 4*30 second exercise protocol: immediately after the first 30 seconds, immediately after the second 30 seconds, immediately after the third 30 seconds, immediately after the fourth 30 seconds.
Mean Power Output	Mean power output during the exercise protocol will be recorded as an indicator of anaerobic performance.	The 4*30 second exercise protocol: immediately after the first 30 seconds, immediately after the second 30 seconds, immediately after the third 30 seconds, immediately after the fourth 30 seconds.
Relative Mean Power Output	Relative mean power output normalized to body mass will be calculated to evaluate anaerobic performance.	The 4*30 second exercise protocol: immediately after the first 30 seconds, immediately after the second 30 seconds, immediately after the third 30 seconds, immediately after the fourth 30 seconds.

Collaborators and Investigators

• Sponsor: Istanbul Sabahattin Zaim University
• Collaborators: T.C. Dumlupınar Üniversitesi
• Investigators: Study Director: Halit HARMANCI, Professor Doctor, Republic of Turkey KUtahya Dumlupınar University

Study record dates

Study Major Dates

• Study Start (Actual): May 9, 2025
• Primary Completion (Actual): May 15, 2025
• Study Completion (Actual): June 5, 2025

Study Registration Dates

• First Submitted: March 13, 2026
• First Submitted That Met QC Criteria: March 19, 2026
• First Posted (Actual): March 25, 2026

Study Record Updates

• Last Update Posted (Actual): March 25, 2026
• Last Update Submitted That Met QC Criteria: March 19, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: Exercise Recovery; High-Intensity Interval Exercise; L-Carnitine Supplementation; Exercise-Induced Muscle Damage; Delayed Onset Muscle Soreness (DOMS)
• Additional Relevant MeSH Terms: Behavior; Motor Activity; Organic Chemicals; Amines; Quaternary Ammonium Compounds; Trimethyl Ammonium Compounds; Carnitine
• Other Study ID Numbers: E-95961207-604.01.01-2245; Kutahya Dumlupınar University (Other Identifier: Kutahya Dumlupınar University Scientific Research Projects Coordination Office)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Data privacy, Ethics committee restrictions, Risk of misinterpretation of data

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No