Effects of Exercise-Induced Muscle Damage on Neuromuscular Complexity (EIMD-NMC)

Effects of Exercise-Induced Muscle Damage Induced by Eccentric Exercise on Knee Extensor Torque, Oxygenation, and Electromyographic Properties: A Complexity-Based Approach

This study will examine the effects of exercise-induced muscle damage, induced by eccentric exercise, on torque production, muscle oxygenation, and electromyographic activity of the knee extensors in healthy young men. Eleven participants will perform a sustained submaximal isometric contraction before and 48 hours after a muscle-damaging eccentric exercise protocol. It is anticipated that the eccentric exercise will confirm the presence of muscle damage, by decrease in maximal voluntary isometric torque, increase in muscle soreness, and reduction in pain-free range of motion. The effect of eccentric exercise on the complexity of torque output, which could be reflected by decreased Sample Entropy and increased DFA α, will be indicated by a possible shift toward more predictable and less adaptable motor control patterns. Based on these results, the investigators will know about the effect of eccentric exercise induced muscle damage on neuromuscular efficiency, that is greater neural input could be required to maintain the same mechanical output, as well as increased oxygen consumption in the active muscle.

Study Overview

• Status: Completed
• Conditions: Muscle Damage; Eccentric Exercise
• Intervention / Treatment: Other: Isokinetic eccentric exercise

Detailed Description

The present study was designed to investigate the impact of exercise-induced muscle damage , caused by eccentric exercise, on neuromuscular and physiological function of the knee extensor muscles. The research was based on the contemporary theoretical framework of the "loss of complexity," which proposes that physiological signal variability is not merely random noise, but rather an essential characteristic of healthy and adaptable biological systems. According to this approach, greater signal complexity reflects a more flexible and efficient neuromuscular control strategy, whereas reduced complexity indicates impaired adaptability and a more rigid functional state.

A total of eleven healthy young men (N = 11, age 27.8 ± 2.5 years) participated in the study. During the initial session, anthropometric characteristics were recorded and maximal voluntary isometric torque of the knee extensors was measured. The main testing procedure involved a sustained submaximal isometric contraction performed at 50% of maximal voluntary contraction for 60 seconds. During this task, torque output, muscle oxygenation, and electromyographic activity of the vastus lateralis were continuously was recorded in order to assess both mechanical and neuromuscular responses.

Following baseline testing, participants completed a muscle damage induction protocol consisting of five sets of fifteen maximal eccentric contractions performed at an angular velocity of 60°/s. This protocol was designed to induce structural and functional muscle impairment characteristic of exercise induced muscle damage. Forty-eight hours after the intervention, all measurements were repeated to determine the effects of muscle damage on the same variables. Data were processed and analyzed in MATLAB, with statistical significance set at p < .05.

The results are anticipated to confirm the successful induction of muscle damage.

The investigators wanted to show the effect of exercise induced muscle damage on torque complexity through changes in Sample Entropy, and changes on detrended fluctuation analysis exponent, which indicate that torque fluctuations will became more regular, predictable, and less complex.

A possible reduction in complexity it expected to be accompanied by a change in neuromuscular efficiency, meaning that a greater level of neural activation will be needed to produce the same relative mechanical output. A likely explanation is that damage to muscle fibers and sarcomeres would reduce the effectiveness of force transmission, forcing the nervous system to compensate through increased neural drive.

In parallel, it is expected that muscle oxygenation measurements will show increased deoxygenated hemoglobin, indicating higher oxygen extraction and a greater metabolic burden on the remaining functional muscle fibers. This finding would suggest that, after exercise induced muscle damage, fewer intact fibers may be available to share the workload, thereby increasing the relative demand placed on those still functioning effectively.

An additional important observation will be the possible changes in traditional linear variability indices, such as standard deviation and coefficient of variation. This will highlight the limitation of conventional linear measures in detecting subtle but functionally meaningful changes in neuromuscular regulation.

• Study Type: Interventional
• Enrollment (Actual): 11
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Greece
  • Attica
    • Athens, Attica, Greece, 17234
      • School of Physical Education and Sport Science

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• No experience of resistance exercise with heavy loads the past 6 months

Exclusion Criteria:

• History of lower-limb injury
• Taking any medication
• Suffered from any pathological condition
• Participation in a systematic eccentric exercise program during the previous 6 months

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: Non-Randomized
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Eccentric exercise; All the parameters that was assessed 48 hours post isokinetic eccentric exercise	Other: Isokinetic eccentric exercise; Isokinetic eccentric exercise consisted of 5 sets of 15 repetitions using the knee extensors. The intensity of the exercise was the maximal voluntary and an interval of 1 minute was applied between sets.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Isokinetic sub maximal exercise	Isokinetic exercise of 60 seconds using the sub maximal intensity of 50% MVC. The knee joint will be set at 90 degrees and the values will be in Nm.	From enrollment to the end of the treatment at 48 hours
Electromyography	Continuous recording of EMG during the 60 seconds isometric exercise. Patches will be placed in vastus laterals and the recording will be at 100 Hz	From enrollment to the end of treatment at 48 hours
Muscle oxygenation	Muscle oxygenation measured using near infrared spectroscopy (NIRS) of the knee extensors during the 60 seconds isometric exercise. The main parameters that will be recored are the oxygenated haemoglobin, the deoxygenated haemoglobin, the total haemoglobin and the difference between oxygenated and deoxygenated haemoglobin.	rom enrollment to the end of treatment at 48 hours

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Delayed onset muscle soreness	Assessment of subjective pain feeling assessed by palpation of knee extensors muscle belly. The scale was set between 1 (no pain at all) to 10 (extreme pain).	From enrollment to the end of treatment at 48 hours
Range of Motion	The angles the knee joint may be flexed without the feeling of any pain. The starting position was set at full extension.	From enrollment to the end of treatment at 48 hours
Peak torque output	Isometric peak torque output was assessed at 90 degrees knee joint angle (0 degrees was set at full extension). The assessments was consisted of 3 set of 5 seconds each. The higher performance was recorded for the data analysis	From enrollment to the end of treatment at 48 hours

Collaborators and Investigators

• Sponsor: National and Kapodistrian University of Athens
• Investigators: Principal Investigator: Vassilis Paschalis, Dr., National and Kapodistrian Univesity of Athens

Study record dates

Study Major Dates

• Study Start (Actual): August 20, 2025
• Primary Completion (Actual): January 20, 2026
• Study Completion (Actual): March 30, 2026

Study Registration Dates

• First Submitted: April 19, 2026
• First Submitted That Met QC Criteria: April 27, 2026
• First Posted (Actual): May 4, 2026

Study Record Updates

• Last Update Posted (Actual): May 4, 2026
• Last Update Submitted That Met QC Criteria: April 27, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

• Keywords: variability; muscle oxygenation; muscle damage; complexity; Peak torque
• Other Study ID Numbers: 1731/19-12-2024

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual Participant Data (IPD) will not be shared with other researchers in order to protect participant confidentiality and privacy, and because no data-sharing plan was included in the study protocol or consent process.

Drug and device information, study documents

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