Effects of Inter-Set Rest Intervals on Muscle Damage After Flywheel Exercise in Untrained Men (RCT)

June 25, 2026 updated by: Federal University of Vicosa

Effects of Different Inter-Set Rest Intervals on Indirect Markers of Muscle Damage and Mechanical Parameters After Flywheel Resistance Training in Untrained Men: A Randomized Parallel-Group Clinical Trial

This randomized parallel-group clinical trial will compare the acute effects of three different inter-set rest intervals during a single lower-limb flywheel resistance exercise session in untrained men. Participants will be randomly allocated to one of three groups: 1-minute, 2-minute, or 3-minute inter-set rest interval. The primary outcome will be the change in maximal voluntary isometric contraction of the knee extensors 48 hours after exercise. Secondary outcomes will include mechanical variables during the exercise session, countermovement jump performance, knee flexor maximal voluntary isometric contraction, muscle soreness, pressure pain threshold, range of motion, ultrasound-derived muscle thickness and echo intensity, perceived exertion, perceived discomfort, perceived recovery status, creatine kinase, and lactate dehydrogenase.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Not yet recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Detailed Description

Participants will complete seven laboratory visits. The first two visits will be used for baseline assessments and test-retest reliability. The third and fourth visits will be used for technical familiarization with the flywheel exercises. The fifth visit will include the experimental flywheel resistance exercise session and immediate post-exercise assessments. The sixth and seventh visits will include follow-up assessments 48 and 96 hours after the experimental session, respectively. Blood samples for creatine kinase and lactate dehydrogenase will be collected before the experimental session and 72 hours after exercise in a partner laboratory.

The experimental session will include squat, Romanian deadlift, knee extension, and knee flexion exercises performed using flywheel devices. All groups will perform the same exercises, volume, inertia, and execution instructions. The only difference between groups will be the inter-set rest interval: 1 minute, 2 minutes, or 3 minutes.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
30

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Brazil
    • Minas Gerais
      • Viçosa, Minas Gerais, Brazil, 36570-900

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Age between 18 and 40 years;
  • Apparently healthy and clinically able to perform physical exercise;
  • No participation in structured resistance training during the previous 6 months;
  • Agreement to comply with all study visits and procedures;
  • Signed informed consent form.

Exclusion Criteria:

  • History of lower-limb musculoskeletal injury or surgery that may impair performance or safety during the proposed exercise protocol;
  • Current pain, injury, or functional limitation in the lower limbs;
  • Use of ergogenic aids that may affect physical performance or muscle recovery;
  • Use of analgesic or anti-inflammatory medication during the study period;
  • Failure to attend the scheduled visits required for the primary outcome assessment.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

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

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Experimental: 1-Minute Inter-set Rest Interval
Participants allocated to this group will perform a single lower-limb flywheel resistance exercise session using a 1-minute inter-set rest interval. The session will include squat, Romanian deadlift, knee extension, and knee flexion exercises.
Behavioral: Flywheel resistance exercise with 1-minute inter-set rest
Participants will perform a single lower-limb flywheel resistance exercise session using a 1-minute inter-set rest interval. The session will include squat, Romanian deadlift, knee extension, and knee flexion exercises. Each exercise will be performed for 4 sets of 2 preparatory repetitions followed by 8 valid repetitions, using the same flywheel inertia, exercise order, and execution instructions across all groups. Participants will be instructed to perform the concentric phase as fast as possible and to brake the eccentric phase during the final portion of the movement. The interval between exercises will be standardized at 3 minutes.
Experimental: 2-Minute Inter-set Rest Interval
Participants allocated to this group will perform a single lower-limb flywheel resistance exercise session using a 1-minute inter-set rest interval. The session will include squat, Romanian deadlift, knee extension, and knee flexion exercises.
Behavioral: Flywheel resistance exercise with 2-minute inter-set rest
Participants will perform a single lower-limb flywheel resistance exercise session using a 2-minute inter-set rest interval. The session will include squat, Romanian deadlift, knee extension, and knee flexion exercises. Each exercise will be performed for 4 sets of 2 preparatory repetitions followed by 8 valid repetitions, using the same flywheel inertia, exercise order, and execution instructions across all groups. Participants will be instructed to perform the concentric phase as fast as possible and to brake the eccentric phase during the final portion of the movement. The interval between exercises will be standardized at 3 minutes.
Experimental: 3-Minute Inter-set Rest Interval
Participants allocated to this group will perform a single lower-limb flywheel resistance exercise session using a 1-minute inter-set rest interval. The session will include squat, Romanian deadlift, knee extension, and knee flexion exercises.
Behavioral: Flywheel resistance exercise with 3-minute inter-set rest
Participants will perform a single lower-limb flywheel resistance exercise session using a 3-minute inter-set rest interval. The session will include squat, Romanian deadlift, knee extension, and knee flexion exercises. Each exercise will be performed for 4 sets of 2 preparatory repetitions followed by 8 valid repetitions, using the same flywheel inertia, exercise order, and execution instructions across all groups. Participants will be instructed to perform the concentric phase as fast as possible and to brake the eccentric phase during the final portion of the movement. The interval between exercises will be standardized at 3 minutes.

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Change in maximal voluntary isometric contraction of the knee extensors
Time Frame: Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Maximal voluntary isometric contraction of the knee extensors will be assessed using a load cell with the knee positioned at 90 degrees of flexion. The primary outcome will be the change in force between baseline and immediately, 48 hours, and 96 hours after the experimental exercise session using a flywheel.
Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Change in maximal voluntary isometric contraction of the knee flexors
Time Frame: Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
The maximum voluntary isometric contraction of the knee flexors will be assessed using a load cell with the knee positioned at 45 degrees of flexion. The primary outcome will be the change in force between baseline and immediately, 48 hours, and 96 hours after the experimental exercise session using a flywheel.
Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Change in vastus lateralis and biceps femoris long head muscle thickness
Time Frame: Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Change in vastus lateralis and biceps femoris long head echo intensity
Time Frame: Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Change in countermovement jump performance
Time Frame: Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Change in active and passive knee flexion and extension range of motion
Time Frame: Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Change in lower-limb muscle soreness score assessed by the Visual Analogue Scale
Time Frame: Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Lower-limb muscle soreness will be assessed using a 100-mm Visual Analogue Scale. The scale ranges from 0 to 100, where 0 indicates no pain and 100 indicates the worst possible pain. Higher scores indicate greater muscle soreness. The outcome will be reported as the change in muscle soreness score from baseline to the post-exercise time points.
Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Change in pressure pain threshold of the thigh muscles
Time Frame: Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Baseline, 10 minutes after the experimental exercise session, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Change in serum creatine kinase and lactate dehydrogenase concentrations
Time Frame: Pre-exercise and 72 hours after the experimental exercise session
Pre-exercise and 72 hours after the experimental exercise session
Peak concentric and eccentric power output during flywheel exercise
Time Frame: During all 16 sets performed in the experimental exercise session
Peak concentric and eccentric power output will be recorded during each valid repetition of the flywheel exercise session using a load cell connected to the flywheel device. Data will be collected for all sets and exercises, excluding the initial preparatory repetitions. The outcome will be reported as peak concentric power, peak eccentric power, and eccentric/concentric power ratio across the experimental exercise session.
During all 16 sets performed in the experimental exercise session
Rating of perceived exertion assessed by the OMNI-Resistance Exercise Scale
Time Frame: After each of the 16 sets performed during the experimental exercise session and 10 minutes after the experimental exercise session
Rating of perceived exertion will be assessed using the OMNI-Resistance Exercise Scale. The scale ranges from 0 to 10, where 0 indicates extremely easy and 10 indicates extremely hard. Higher scores indicate greater perceived exertion. The outcome will be reported after each set of the experimental flywheel exercise session and 10 minutes after the end of the session.
After each of the 16 sets performed during the experimental exercise session and 10 minutes after the experimental exercise session
Perceived discomfort assessed by the Discomfort Scale
Time Frame: After each of the 16 sets performed during the experimental exercise session and 10 minutes after the experimental exercise session
Perceived discomfort will be assessed using a 0-to-100 Discomfort Scale. The scale ranges from 0 to 100, where 0 indicates no discomfort and 100 indicates maximal discomfort. Higher scores indicate greater perceived discomfort. The outcome will be reported after each set of the experimental flywheel exercise session and 10 minutes after the end of the session.
After each of the 16 sets performed during the experimental exercise session and 10 minutes after the experimental exercise session
Perceived recovery status assessed by the Perceived Recovery Status Scale
Time Frame: Baseline, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session
Perceived recovery status will be assessed using the Perceived Recovery Status Scale. The scale ranges from 0 to 10, where 0 indicates very poor recovery and 10 indicates full recovery. Higher scores indicate better perceived recovery. The outcome will be reported as the perceived recovery status score at baseline and at the post-exercise follow-up time points.
Baseline, 48 hours after the experimental exercise session, and 96 hours after the experimental exercise session

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Federal University of Vicosa

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
June 1, 2026

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
July 1, 2026

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
July 1, 2026

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
May 29, 2026

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
June 25, 2026

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
July 1, 2026

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
July 1, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
June 25, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
May 1, 2026

More Information

Terms related to this study

Keywords

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • 7.151.525 (Other Identifier: Ethics Committee Approval Number)
  • 81740024.5.0000.5153 (Other Identifier: CAAE)

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

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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