Swimmers performed a 15m swim start after each warm-up protocol. The control protocol consisted of a swim-specific warm-up (SW). One experimental protocol only included post-activation performance enhancement (PAPE). Another experimental protocol consisted of a swim-specific warm-up followed by post-activation performance enhancement (SW+PAPE). In the experimental protocols, the swim start was preceded by a PAPE induced by performing three series of jumps of 5 jumps while the controls performed the start without PAPE.
The sample for this study consisted of ten national-level male swimmers (age, 16 ± 2 years; height, 1.75 ± 0.07 m; body mass, 64.33 ± 6.08 kg). All participants had at least five years of racing experience. Participants completed eight training sessions per week, up to 2 hours per session. General swimming-specific conditioning and instructional training was carried out in the pool. Dry-field conditioning consisting of bodyweight exercises (squats, lunges, push-ups, and bilateral jumps) was performed twice a week for 30 minutes. All participants had no previous experience of heavy resistance training. The participants knew the test protocol and, at the time of the experiment, they were in good health and without any injuries. The experimental procedures reported in this study were performed in accordance with the ethical standards of the Declaration of Helsinki, and the participants and their parents signed informed consent forms. The experimental protocols were approved by the Ethics Committee of the Faculty of Sports and Physical Education of the University of Niš, Serbia.
Swim specific warm up (SW)
The total SW volume was set at 1,600 m. The SW consisted of 400m freestyle/backstroke (75m freestyle/25m backstroke), 2 × 100m individual medley (25m butterfly/25m backstroke/25m breaststroke/25m freestyle) with 20 s rest in between 200m front crawl exercises (25m easy/25m fast), 200m front crawl kick with a board (25m fast/25m easy), 4 × 50 m front crawl for 60 s (2 easy and 2 medium), 4 × 50 m front crawl with a starting block (one dive followed by 15 m fast/35 m easy) for 90 s, and 200 m easy swim with fins . A pre-competition warm-up is an integral part of every competition, usually an active pool warm-up that represents preparation for competitions and enhances athlete performance.38.39.
Drop Jump Protocol (PAPE)
The drop jump (DJ) was performed from an individualized box height according to the previously assessed physical capacity of the participants (40 cm). Participants performed three sets of 5 reps based on recommendations from a previous study30. The recovery between repetitions was no more than 15 s, while the pause between sets was 120 s. Drop jumps were performed by bouncing to minimize ground contact time40. Participants were suggested to use explosive arm swings to maximize their drop jump performance.
Before the experiment, and regardless of the protocol, it was necessary to carry out familiarization, to determine the continuity of CMY performance on the force platform and to exclude the influence of discontinuous performance on the results. of research. The first measurement was taken after a general warm-up. To ensure that the effects of PAPE came directly from the DJ and not from another protocol, swimmers performed 3 CMJs, each spaced 60 s apart. Intraclass correlation coefficients for test-retest reliability and typical errors for JH, PP, RSImod, ERFD and IES were 0.94, 0.96, 0.90, 0.98 and 0.99 and 2.76 , 2.66, 0.04, 5.16 and 4.56, respectively. After 48 h of recovery, the second measurement took place. The intraclass correlation coefficients for test-retest reliability and standard error for the 15 m swim start were 0.97 and 0.38, respectively.
The third, fourth and fifth measurements were the actual experimental measurements. Recovery between different warm-up protocols was not less than 48 h to allow adequate recovery. In addition, the participants did not undergo intensive training 48 h before the experiment, nor consumed cigarettes, alcohol or stimulants. The warm-up protocols were implemented in the following order: SW, PAPE and SW + PAPE. Testing procedures were always performed at the same time of day to exclude diurnal changes in performance. In addition, the tests were carried out under the same conditions (temperature, humidity, equipment). In the SW + PAPE protocol, participants performed PAPE 8 min after completing the SW. Instead of SW, the PAPE protocol included a general warm-up (10 min of light jumping, dynamic stretching, and general movement). Participants rested passively for 8 min after the protocols and performed the T15m test10.17.
Swimming start at 15m
On three separate days, divided by 48h recovery, swimmers completed a 15m swim start test, preceded by the warm-up protocols previously explained. The track start was adopted in all conditions. Participants were asked to perform a maximum effort dive, an underwater kick and a freestyle to the 15m mark. The specifications of the starting block were as follows: the height above the water surface was 0.72 m above the water surface, with a platform of 0.5 × 0, 5 m and an inclination of 8°. The Alge Swim Time platform (SO2-X, Alge Timing—Austria) which measures start reaction was placed on the starting block platform. Time was measured in seconds. Prior to making each start, the participant was instructed, by verbal command, of a position on the starting block. For greater efficiency, the participants performed the swimming start with maximum freestyle intensity, even a few meters after the 15 m mark.
To collect the swim start parameters, we used two digital cameras. A CASIO FX camera that records 300 frames per second was used for the kinematic analysis of the swim start. The camera was placed in the sagittal plane and perpendicular to starting lane 8. In addition, the camera was static and set on the horizontal optical axis, approximately 1 m in front of the vertical plane of the leading edge of the starting block and 1 m above the water surface. The second, a Canon RT digital video camera, which records 60 frames per second, was placed perpendicular to the 15m line from the starting block, and its role was to record the moment the participant’s head crossed the 15m mark. Both cameras recorded continuously during each test protocol. The cameras were configured to record visual and audio signals. Alge Timing emits the start-up sound signal and a simultaneous visual flash from a stroboscope placed in front of the cameras.
Kinematic analysis of the swim start was performed using 2D kinematic analysis computer software (Dartfish, v. 126.96.36.199, Fribourg, Switzerland).
Parameters measured for swim start performance were 15m time (T15m, time from start signal to swimmer’s head crossing the 15m mark) and entry time (ET, time from first contact with water to full body entry).
Jump in countermovement
The CMJ was used to measure the power of the lower limbs, with a force plate (Kistler, QuattroJump 9290DD, Winterthur, Switzerland), with a sampling rate of 500 Hz. Before performing the jump, the participants had to put their hands on their hips. The CMJ was carried out in the pool, in swimsuits and barefoot to bring the measurement procedure closer to real conditions and to obtain good ecological validity.
Prior to performing the CMJ, participants stood still on a force platform (Kistler QuattroJump) for more than one second to measure their body weight (N)41. Ground reaction force (GRF) raw data was exported for processing in custom software (MATLAB, v. R2018a (188.8.131.523654), MathWorks, Inc., Natick, Massachusetts, USA). Vertical GRF data was extracted only along the vertical axis (Fz). After extracting the raw Fz from a force plate, the data was smoothed using a fourth-order low-pass Butterworth digital filter with a cutoff frequency of 50 Hz.42. The Fz jump profile was divided into unloading, eccentric (cession and braking) and concentric phases (Fig. 5). The beginning of the movement43the start of braking and the concentric phase41and contact time43 were determined with the methods proposed in a recent study.
The parameters measured were jump height (JH), modified reactive strength index (RSImod), peak power (PP), eccentric rate of strength development (ERFD) and explosive strength index (IES). ). All calculations of the dependent variables are shown in Table 2.
All data analyzes were performed using SPSS statistical package for the social sciences (IBM SPSS, version 23.0; IBM SPSS, Armonk, NY, USA). Means, standard errors and the Kolmogorov-Smirnov test were calculated. Differences were compared using one-way repeated measures ANOVA and Bonferroni’s method. Effect size (ES) and percent change in performance were also calculated. Additionally, the smallest significant effect for each dependent variable was applied to observe the actual change in performance. The smallest significant effect was defined as the smallest valid change deemed practically significant for swimmers. For each effect, the threshold value for the smallest significant effect was 0.2. The probabilities that the actual performance difference was harmful, insignificant, or beneficial were expressed as percentages, reflecting the following descriptors: 1%, almost certainly not; 1-5%, very unlikely; 5–25%, unlikely; 25 to 75%, optionally; 75-95%, probably; 95–99%, very likely; 0.99%, almost certainly44.
The Ethics Committee of the Faculty of Sports and Physical Education of the University of Niš, Serbia, obtained an ethical review and approval. The experimental procedures reported in this study were performed in accordance with the ethical standards of the Declaration of Helsinki, and the participants and their parents signed informed consent forms.