Skip to main content
OpenTrials
Not Yet Recruiting

NCT Number: NCT07679971

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

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.

Not Yet Recruiting

Trial opening soon.

Get Notified

Key information

Conditions

Exercise-induced Muscle Damage

Age range

18 year–40 year

Sex eligibility

Male

Study type

Interventional

Phase

Not applicable

Primary location

About this study

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.

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

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.

Treatment and study plan

Flywheel resistance exercise with 1-minute inter-set rest

Behavioral

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.

Flywheel resistance exercise with 2-minute inter-set rest

Behavioral

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.

Flywheel resistance exercise with 3-minute inter-set rest

Behavioral

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.

Primary outcomes

  1. 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.

  2. 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.

Secondary outcomes

  1. 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

  2. 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

  3. 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

  4. 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

  5. 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.

  6. 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

  7. Change in serum creatine kinase and lactate dehydrogenase concentrations

    Time frame: Pre-exercise and 72 hours after the experimental exercise session

  8. 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.

  9. 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.

  10. 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.

  11. 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.

Sponsors and collaborators

Lead sponsor

Federal University of Vicosa

Other

Registry information

Official study title

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

Important dates

Study start
2026
Primary completion
2026
Study completion
2026
First posted
Jul 1, 2026
Registry last updated
Jul 1, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

Related clinical trials

Published trials that share one or more normalized conditions with this study.