Acute Muscle Damage After Eccentric Quasi-Isometric Exercise of the Elbow Flexors

Acute Muscle Damage Responses in Elbow Flexors Following Eccentric Quasi-isometric Exercise

This study compared the acute muscle damage responses of the elbow flexor muscles following two types of resistance exercise: eccentric quasi-isometric (EQI) exercise and traditional eccentric (ECC) exercise. Thirty healthy young men were randomly assigned to perform either EQI or ECC using a dumbbell elbow flexion exercise. Both groups exercised with the same relative external load and performed the exercise to voluntary fatigue.

Muscle function, muscle soreness, and blood markers related to muscle damage were assessed before exercise, immediately after exercise, and over a 7-day recovery period. The purpose of this study was to examine whether EQI exercise, which involves a prolonged isometric phase followed by a very slow eccentric action, induces different levels of acute muscle damage and recovery compared with traditional eccentric exercise.

Study Overview

• Status: Completed
• Conditions: Acute Muscle Damage Following Resistance Exercise
• Intervention / Treatment: Behavioral: Eccentric Quasi-Isometric Exercise; Behavioral: Traditional Eccentric Exercise

Detailed Description

Eccentric resistance exercise is widely used in strength training but is often associated with substantial exercise-induced muscle damage, resulting in strength loss, muscle soreness, swelling, and prolonged recovery. Eccentric quasi-isometric (EQI) exercise is a recently proposed contraction mode that combines a sustained isometric hold with a subsequent extremely slow eccentric lengthening under continuous voluntary resistance. This contraction pattern results in prolonged time under tension while avoiding rapid lengthening or abrupt force spikes.

In this randomized interventional study, thirty healthy young men with no recent resistance training experience were randomly assigned to perform either EQI or traditional eccentric (ECC) exercise of the elbow flexors. Participants performed unilateral dumbbell elbow flexion exercise at 70% of their one-repetition maximum. The EQI group completed five sets of single repetitions consisting of an initial isometric hold at 90 degrees of elbow flexion until task failure, followed by very slow eccentric lengthening to full elbow extension. The ECC group performed five sets of repeated eccentric-only elbow flexion exercises at a controlled tempo until failure. Rest intervals were standardized between sets.

Muscle damage and recovery were evaluated using multiple functional and biochemical indicators, including maximal voluntary isometric contraction torque, elbow joint range of motion, upper arm circumference, pressure pain threshold, and circulating concentrations of creatine kinase and myoglobin. Measurements were obtained before exercise, immediately after exercise, and at 1, 2, 3, and 7 days following the exercise bout.

The primary objective of this study was to compare the acute muscle damage responses and recovery profiles of the elbow flexors following EQI and ECC exercise when performed to voluntary fatigue at the same relative external load.

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

Contacts and Locations

Study Locations

• Taiwan
  • Taiwan
    • Taipei, Taiwan, Taiwan, 11114
      • Chinese Culture University

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Healthy young men
• Age between 20 and 30 years
• No participation in any regular exercise training programs during the previous 12 months
• No history of cardiovascular disease, diabetes mellitus, liver disease, respiratory disorders, neuromuscular disease, or musculoskeletal disorders
• No long-term use of chronic prescription medications
• No history of dizziness, chest discomfort, or falls during physical activity
• Not previously diagnosed by a physician as unsuitable for exercise

Exclusion Criteria:

• History of upper limb musculoskeletal, joint, or bone injuries
• Inability to independently perform activities of daily living
• Presence of cardiovascular, metabolic, respiratory, neuromuscular, or musculoskeletal disorders
• Requirement for assistive devices for ambulation in daily life
• Previous medical diagnosis indicating unsuitability for exercise participation
• Presence of acute illness at the time of enrollment
• History of major surgery within the past 12 months
• Severe physical injury that could impair exercise performance or daily activities

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: eccentric quasi-isometric (EQI); Participants assigned to this arm performed eccentric quasi-isometric (EQI) exercise of the elbow flexors using a unilateral dumbbell preacher curl. The external load was set at 70% of each participant's one-repetition maximum. Each repetition began with a sustained isometric hold at 90 degrees of elbow flexion until task failure, followed immediately by a very slow eccentric lengthening to full elbow extension while participants continued to resist the load. Participants completed five sets of one repetition, with 90 seconds of rest between sets. All repetitions were performed to voluntary fatigue under supervision.	Behavioral: Eccentric Quasi-Isometric Exercise; Eccentric quasi-isometric (EQI) exercise of the elbow flexors was performed using a unilateral dumbbell preacher curl. The external load was set at 70% of each participant's one-repetition maximum. Each repetition began with a sustained isometric contraction at 90 degrees of elbow flexion until task failure, followed immediately by a very slow eccentric lengthening to full elbow extension while participants continued to resist the load. One repetition was defined as the continuous task from the onset of the isometric hold to full elbow extension. Participants completed five sets of one repetition with 90 seconds of rest between sets. All repetitions were performed to voluntary fatigue under supervision.
Active Comparator: Traditional Eccentric Exercise (ECC); Participants assigned to this arm performed traditional eccentric-only exercise of the elbow flexors using a unilateral dumbbell preacher curl. The external load was set at 70% of each participant's one-repetition maximum. From a starting position of 90 degrees of elbow flexion, participants repeatedly lowered the dumbbell through the full range of motion using controlled eccentric contractions at a cadence of approximately 2.5 seconds per repetition, guided by a metronome. Each set was performed to voluntary failure, and a total of five sets were completed with 90 seconds of rest between sets.	Behavioral: Traditional Eccentric Exercise; Traditional eccentric-only exercise of the elbow flexors was performed using a unilateral dumbbell preacher curl. The external load was set at 70% of each participant's one-repetition maximum. From a starting position of 90 degrees of elbow flexion, participants repeatedly lowered the dumbbell through the full range of motion using controlled eccentric contractions at a cadence of approximately 2.5 seconds per repetition, guided by a metronome. Each set was performed to voluntary failure, and a total of five sets were completed with 90 seconds of rest between sets.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Maximal Voluntary Isometric Contraction (MVC) Torque	Maximal voluntary isometric contraction (MVC) torque of the elbow flexors was assessed using an isokinetic dynamometer with the elbow positioned at 90 degrees of flexion. Participants performed three maximal 3-second isometric contractions with standardized verbal encouragement. The highest torque value obtained across trials was used for analysis as an indicator of muscle function and strength loss following exercise.	Baseline (Day 0) and Days 1, 2, 3, and 7

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Elbow Joint Range of Motion (ROM)	Elbow joint range of motion (ROM) was assessed using a manual goniometer by measuring the relaxed elbow joint angle and the fully flexed elbow joint angle. ROM was calculated as the difference between these two angles and used as an indicator of joint mobility restriction following exercise-induced muscle damage.	Baseline (Day 0) and Days 1, 2, 3, and 7
Upper Arm Circumference (CIR)	Upper arm circumference (CIR) was measured at the midpoint between the acromion and the lateral epicondyle with the arm relaxed and extended. Circumference measurements were used as an indirect indicator of muscle swelling following exercise.	Baseline (Day 0) and Days 1, 2, 3, and 7
Pressure Pain Threshold (PPT)	Pressure pain threshold (PPT) of the elbow flexors was assessed using a digital pressure algometer at the proximal, middle, and distal regions of the biceps brachii. PPT values were used to quantify changes in pain sensitivity following exercise.	Baseline (Day 0) and Days 1, 2, 3, and 7
Plasma Creatine Kinase (CK)	Plasma creatine kinase (CK) activity was measured from venous blood samples using an automated clinical chemistry analyzer. CK concentration was used as a biochemical marker of muscle membrane disruption following exercise.	Baseline (Day 0) and Days 1, 2, 3, and 7
Plasma Myoglobin (Mb)	Plasma myoglobin (Mb) concentration was determined from venous blood samples using a chemiluminescent immunoassay. Myoglobin levels were used as a biochemical indicator of muscle damage following exercise.	Baseline (Day 0) and Days 1, 2, 3, and 7
Time Under Tension (TUT)	Time under tension (TUT) was recorded during the exercise session as the total duration of muscle contraction. TUT was measured for each exercise set and used to characterize differences in contraction duration between exercise conditions.	Day 1

Collaborators and Investigators

• Sponsor: Chinese Culture University

Study record dates

Study Major Dates

• Study Start (Actual): August 1, 2020
• Primary Completion (Actual): August 1, 2021
• Study Completion (Actual): August 1, 2021

Study Registration Dates

• First Submitted: February 10, 2026
• First Submitted That Met QC Criteria: February 21, 2026
• First Posted (Actual): February 25, 2026

Study Record Updates

• Last Update Posted (Actual): February 25, 2026
• Last Update Submitted That Met QC Criteria: February 21, 2026
• Last Verified: February 1, 2026

More Information

Terms related to this study

• Keywords: Resistance exercise; Muscle fatigue; Exhaustive exercise; Mechanical tension; Contraction characteristics
• Other Study ID Numbers: PCCU; MOST 109-2410-H-034-041 (Other Grant/Funding Number: National Science and Technology Council)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

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