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

Official 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

Overview

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.

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.

Interventions

• 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 possi
• 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 possi
• 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 possi

Primary outcome measures

• 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]
• 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]

Secondary outcome measures (11)

• 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]
• 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]
• 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]
• 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]
• 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]
• 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]
• Change in serum creatine kinase and lactate dehydrogenase concentrations [Time frame: 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]
• 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]
• 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 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]

Eligibility criteria

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.

Criteria are shown verbatim from the registry (in English). Final eligibility is always assessed by the study center.

Healthy volunteers: Yes

Study design

Allocation

Randomized

Model

Parallel assignment

Masking

Open label

Primary purpose

Basic science

Study locations

Brazil · 1 center

• Federal University of Viçosa — Viçosa

Identifiers

NCT: NCT07679971 · 7.151.525 · 81740024.5.0000.5153 · 7.151.525

Primary sources (government registries)

• ClinicalTrials.gov (US NIH)

View this study on ClinicalTrials.gov ↗