Acute Effects of Different Warm-Up Protocols in Competitive Young Swimmers

Initially, the athlete stands upright on a flat surface or force platform, feet shoulder-width apart, hands on hips (to eliminate arm swing). Without a pause, the athlete performs a quick downward movement (countermovement) by bending the knees and hips, then immediately jumps vertically as high as possible. The athlete lands in an upright position on the same spot, trying to absorb the impact with knees slightly bent. Jump height and flight time is recorded using an optical system, Optojump™ system(Microgate, Bolzano, Italy) connected to a personal computer with dedicated software(OptojumpTM Next software). The system consists of two optical bars, a receiver and a transmitter, positioned 1m apart. The bars identify ground contact time(with a precision of 1ms) and then convert non-contact time into cm. Based on recommendations on optimal jump height (20 to 60cm).

In a second moment, after establishing the best warm-up protocol (from among those proposed) with the best recovery (derived from the CMJ height with the time ratio) for each individual, the 25, 50, and 100 m measurements will be evaluated in the pool. This will take place at a later stage in a 25 m pool. The first part of the warm-up will be the same for all subjects, while the second part will be personalized, based on their Post Activation Performance Enhancement.

The FLIR Foedge thermal imaging camera will be used to capture high-resolution thermal images of the target muscle area under controlled environmental conditions. The thermal imaging camera will be positioned approximately 0.5 meters from the subject's skin surface, with a fixed focal length lens to ensure sharp images. The room will be continuously monitored for temperature and humidity, minimizing external thermal influences. Ambient lighting will be kept low to avoid thermal interference from light sources. The thermal imaging camera will be calibrated before each session, connected to the same smartphone, and images will be captured at a frequency of 30 Hz to monitor temperature changes in real-time before and after muscle activity.

Heart rate (HR) will be measured with a Polar H10 chest strap sensor, a device known to give accurate results. To prepare, participants were asked not to drink coffee or alcohol, avoid hard exercise for 24 hours, and keep their normal sleep routine. The tests will always be done at the same time of day in every condition to avoid daily rhythm effects. The average HR over two minutes of recording will be recorded. The chest strap will be placed just below the chest bone and secured around the chest. Once the signal was ready, data will sent automatically to a mobile app (Elite HRV). All data will be later analyzed with special software (Kubios HRV).

The Moxy oxygen sensor will be positioned on the vastus lateralis portion of the quadriceps muscle to monitor muscle oxygenation dynamics before, during and after exercise. The probe will be securely attached using the appropriate elastic band to minimize motion artifact and oriented parallel to the muscle fibers. Data acquisition will performed at a sampling rate of 10 Hz, capturing relative changes in muscle oxygen saturation (SmO2) and total hemoglobin concentration. The site will be carefully cleaned and shaved when necessary to ensure optimal sensor contact. This setup allows for real-time, non-invasive assessment of local muscle oxygen utilization and hemodynamics, which is useful for evaluating muscular fatigue and metabolic responses.

The Rate of Perceived Exertion (RPE) scale will be employed to assess participants' subjective perception of exercise intensity during the protocol. The Borg Scale will be used following the pool warm-up, before each testing session, after each testing session, and at study conclusion.