Jump height and peak isometric force changes after different combinations of training volume and training intensities using velocity-based training in a flywheel half-squat exercise

INTERVENTION: Randomised flywheel half‐squat exercise, with different combinations of three velocity losses thresholds (5%, 10% and 15%) and three external loads or moments of inertia (0.05 kg·m2, 0.10 kg·m2, and 0.15 kg·m2). More specifically, the combinations will be: 1. Combination 1: Velocity Loss 5%, 0.05 kg·m2 moment of inertia 2. Combination 2: Velocity Loss 5%, 0.10 kg·m2 moment of inertia 3. Combination 3: Velocity Loss 5%, 0.15 kg·m2 moment of inertia 4. Combination 4: Velocity Loss 10%, 0.05 kg·m2 moment of inertia 5. Combination 5: Velocity Loss 10%, 0.10 kg·m2 moment of inertia 6. Combination 6: Velocity Loss 10%, 0.15 kg·m2 moment of inertia 7. Combination 7: Velocity Loss 15%, 0.05 kg·m2 moment of inertia 8. Combination 8: Velocity Loss 15%, 0.10 kg·m2 moment of inertia 9. Combination 9: Velocity Loss 15%, 0.15 kg·m2 moment of inertia Each participant will execute three combinations on a single session, repeated twice a week, with 48‐72h interspersed (wash‐out period). Each session will last about 60 min per participant, and the total intervention duration will be five weeks. Each session will be attended by pairs. The flywheel device will be a cylindrical shaft FRTD (Kbo X3, Exxentrix, Sweeden), with a load range ranging from 0.005 to 0.300 kg·m2 and an axis radius width of 0.025 m, monitored with a rotary encoder (SmartCoach Lite, SmartCoach Tech, USA). The main intervention will be supervised by a sport scientist with expertise in the execution of resistance training with flywheel devices. CONDITION: Cardiovascular ‐ Normal development and function of the cardiovascular system Exercise‐induced neuromuscular changes; ; Exercise‐induced neuromuscular changes Musculoskeletal ‐ Normal musculoskeletal and cartilage development and function PRIMARY OUTCOME: Jump height (CMJ)[Participants will execute CMJ in a contact mat (Chronojump Contact Platform Kit DIN‐A2, Chronojump, Barcelona, Spain). The participants will jump twice in each temporary assessment (Pre, Post0, and Post5). Participants will be instructed to perform a quick stretch‐shortening cycle, with a free‐fall distance, trying to jump as high as possible. Jumps with incorrect technique (e.g., flexing knees or ankles during the flight phase or moving horizontally from the starting position) will not be considered. Jump height will be calculated by the manufacturer's software (Chronojump 2.3.0‐39, Chronojump, Barcelona, Spain). The trial outcome will be selected as the mean of the two jumps, interspersed 30 seconds along each trial. baseline and immediate post‐exercise in every combination execution throughout the intervention period (two times a week for 3 weeks)] Maximum rate of force development (MRFD)[To determine the force production capacity of the lower limbs, an isometric squat test will be used. Participants will remain in a static position at 90º of knee and hip flexion, wearing the same harness flywheel used for the main exercise. A strain gauge (Chronojump, BoscoSystem, Madrid, Spain) will be attached to the harness and to the floor using chains, which will allow standardization of the individual squat position. The strain gauge will have a capacity of 500 kg, a 24‐bit digital analog converter, and 80 Hz. For that reason, participants will be instructed to hold the chains in pretension to avoid any countermovement once they start pulling. After one second of pretension ( 100 N), participants will have to pull with the instruction of 'as fast and hard as possible' for three seconds. Before each training session, the participants will perform two sets, with one minute of recovery between each set in a sitting position. After each VL, they will only execute once to stabilize baseline values and avoid extra fatigue after measurement. The raw data will be acquired using the manufacturer’s software (Chronojump, Barcelona, Spain) and exported to Matlab (version. 2023a) to calculate MRFD with a custom Matlab routine. MRFD will be calculated as the highest slope of the force‐time curve from the onset to the peak force. The execution onset will be established as 10N baseline and immediate post‐exercise in every combination execution throughout the intervention period (two times a week for 3 weeks)] Peak isometric force (PIF)[To determine the force production capacity of the lower limbs, an isometric squat test will be used. Participants will remain in a static position at 90º of knee and hip flexion, wearing the same harness flywheel used for the main exercise. A strain gauge (Chronojump, BoscoSystem, Madrid, Spain) will be attached to the harness and to the floor using chains, which will allow standardization of the individual squat position. The strain gauge will have a capacity of 500 kg, a 24‐bit digital‐analog converter, and 80 Hz. For that reason, participants will be instructed to hold the chains in pretension to avoid any countermovement once they start pulling. After one second of pretension ( 100 N), participants will have to pull with the instruction of 'as fast and hard as possible' for three seconds. Before each training session, the participants will perform two sets, with one minute of recovery between each set in a sitting position. After each VL, they will only execute once to stabilize baseline values and avoid extra fatigue after measurement. The raw data will be acquired using the manufacturer’s software (Chronojump, Barcelona, Spain) and exported to Matlab (version. 2023a) to calculate PIF with a custom Matlab routine. PIF will be calculated as the average of the highest values during one second. The execution onset will be established as 10N baseline and immediate post‐exercise in every combination execution throughout the intervention period (two times a week for 3 weeks)] SECONDARY OUTCOME: mean velocity [Using the smartcoach rotary encoder, we will monitor each repetition providing real time feedback using the mean velocity assessed continuously throughout every exercise combination during the exercise execution component completed throughout the intervention period (two times a week for 3 weeks)] INCLUSION CRITERIA: Participants will be required to be at least 18 years old and to have been participating regularly in physical activities that engage the muscles of the lower limbs for a minimum of the last si Xmonths. The participants will have previous experience in performing the main exercise (a minimum of three months, twice a week).