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.
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;
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;
Parallel
Flywheel resistance exercise with 1-minute inter-set rest
BehavioralParticipants 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
BehavioralParticipants 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
BehavioralParticipants 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.
Change in maximal voluntary isometric contraction of the knee extensors
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.
Change in maximal voluntary isometric contraction of the knee flexors
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.
Change in vastus lateralis and biceps femoris long head muscle thickness
Change in vastus lateralis and biceps femoris long head echo intensity
Change in countermovement jump performance
Change in active and passive knee flexion and extension range of motion
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