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The effects of post-activation performance enhancement and different warm-up protocols on swim start performance

experimental design

The swimmers performed a swim start at 15 m after each warm-up protocol. The control protocol consisted of a swim-specific warm-up (SW). One experimental protocol included only 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 PAPE induced by performing three series of 5 drop jumps, while the controls performed the start without PAPE.

Participants

The sample for this study was composed of ten national-level male swimmers (age, 16 ± 2 years; stature, 1.75 ± 0.07 m; body mass, 64.33 ± 6.08 kg). All of the participants had at least five years of competition experience. The participants underwent eight training sessions per week, up to 2 h per session. General swim-specific conditioning and instructional training were performed in the swimming pool. Dry-land conditioning consisting of bodyweight exercises (squats, lunges, push-ups, and bilateral jumps) was performed twice a week for 30 min. All of the participants had no previous experience in heavy-resistance training. The participants were familiar with the testing protocol, and at the time of the experiment, they were healthy and without any injury. The experimental procedures reported in this study were performed following 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 Sport and Physical Education, University of Niš, Serbia.

Experimental procedures

Swim-specific warm-up (SW)

The total volume of SW was set at 1,600 m. The SW consisted of swimming 400 m free/back light swim (75 m freestyle/25 m backstroke), 2 × 100 m individual medley (25 m fly/25 m back/25 m breast/25 m free) with 20 s rest in between, 200 m of front-crawl drills (25 m easy/25 m fast), 200 m of front-crawl kick using a kickboard (25 m fast/25 m easy), 4 × 50 m front-crawl for 60 s ( 2 easy and 2 medium), 4 × 50 m front-crawl using a starting block (a dive followed by 15 m fast/35 m easy) for 90 s, and a 200 m easy swim using fins. A pre-competition warm-up is an integral part of every competition, typically an active pool-based warm-up that represents preparation for competitive events and enhances the performance of the athletes38.39.

Drop jump protocol (PAPE)

The drop jump (DJ) was performed from an individualized box height based on the participants’ previously evaluated physical ability (40 cm). The participants performed three sets of 5 repetitions based on the recommendations of a previous study.30. The recovery between repetitions was not longer than 15 s, while the break between sets was 120 s. Drop jumps were performed bouncingly to minimize the ground contact time40. It was suggested to the participants that they employ explosive arm swings to maximize their drop jump performance.

Before the experiment, and regardless of the protocol, it was necessary to conduct familiarisation, determine continuity in the CMJ performance on the force plate, and exclude the influence of discontinuous performance on the research results. The first measurement was conducted after a general warm-up. To ensure that the effects of the PAPE came directly from the DJ and not from any other protocol, the swimmers performed 3 CMJs, each separated by 60 s. The intraclass correlation coefficients for test–retest reliability and typical errors for the 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 typical error for the swim start to 15 m were 0.97 and 0.38, respectively.

The third, fourth, and fifth measurements were the actual experimental measurements. The recovery between different warm-up protocols was not shorter than 48 h to allow adequate recovery. Moreover, the participants did not undergo intensive training 48 h prior to the experiment, nor did they consume cigarettes, alcohol, or stimulants. 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, testing was performed under the same conditions (temperature, humidity, equipment). In the SW + PAPE protocol, the participants performed PAPE 8 min after completing the SW. Instead of SW, the PAPE protocol included a general warm-up (10 min of light skipping, dynamic stretching, and general movement). The participants rested passively for 8 min after the protocols and performed the T15m test.10.17.

measurements

Swim start to 15 m

On three separate days, divided by 48 h of recovery, the swimmers performed a 15-m swim start test, preceded by the previously explained warm-up protocols. Track start was adopted through all conditions. The participants were instructed to perform a maximum effort dive, underwater kick, and freestyle swim to the 15-m mark. The starting block specifications were as follows: the height above the water surface was 0.72 m from the water surface, with a 0.5 × 0.5 m platform and an 8° inclination. The Alge Swim Time platform (SO2-X, Alge Timing—Austria) that measures the start reaction was placed on the start block platform. Time was measured in seconds. Before performing each start, the participant was instructed, by a verbal command, to a position on the starting block. For better efficiency, the participants performed the swimming start with maximum freestyle intensity, even a few meters after the 15-m mark.

To collect the parameters of the swim start, 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. Moreover, the camera was static and adjusted to 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 15-m line from the starting block, and its role was to record the moment the participant’s head passed through the 15-m mark. Both cameras were recording continuously during each testing protocol. The cameras were set up to record visual and audio signals. Alge Timing emits the audio start signal and a simultaneous visual flash from a strobe placed opposite the cameras.

Kinematic analysis of the swim start was performed using computer software for 2D kinematic analysis (Dartfish, v. 4.5.2.0, Friborg, Switzerland).

The measured parameters for the swim start performance were time at 15 m (T15m, time from the start signal until the moment when the swimmer’s head passes through the 15-m mark) and entry time (ET, time from the first contact with the water to full body entry).

countermovement jump

The CMJ was used to measure the power of the lower extremities, with a force plate (Kistler, QuattroJump 9290DD, Winterthur, Switzerland), with a sampling rate of 500 Hz. Before performing the jump, the participants were instructed to put their hands on their hips. The CMJ was performed at the swimming pool, in a swimsuit and barefoot to bring the measurement procedure closer to actual conditions and achieve good ecological validity.

Before performing the CMJ, the participants stood motionless on a force plate (Kistler QuattroJump) for more than one second to measure their body weight (N)41. Raw ground reaction force (GRF) data were exported for processing into custom adapted software (MATLAB, v. R2018a (9.4.0.813654), MathWorks, Inc., Natick, Massachusetts, USA). Vertical GRF data were extracted only along the vertical axis (Fz). After extracting raw Fz from a force plate, the data were smoothed using a fourth-order low pass Butterworth digital filter with a cut-off frequency of 50 Hz42. The Fz jump profile was divided into unloading, eccentric (yielding and braking), and concentric phases (Fig. 5). The onset of movement43the onset of braking and the concentric phase41and contact time43 were determined with the methods proposed in a recent study.

The measured parameters were jump height (JH), the reactive strength index modified (RSImod), peak power (PP), the eccentric rate of force development (ERFD), and the index of explosive strength (IES). All dependent variable calculations are presented in Table 2.

Table 2 Calculation of dependent variables.

Statistical analysis

All data analyzes were carried out using the SPSS Statistical Package for Social Sciences (IBM SPSS, version 23.0; IBM SPSS, Armonk, NY, United States). Means, standard errors, and the Kolmogorov–Smirnov test were computed. Differences were compared by using the one-way repeated-measures ANOVA and the Bonferroni method. Effect size (ES) and percentage of change in performance were also computed. Moreover, the smallest important effect for each dependent variable was applied to observe the actual change in performance. The smallest important effect was defined as the smallest worthwhile change deemed practically significant to the swimmers. For each effect, the threshold value for the smallest important effect was 0.2. The probabilities that the actual difference in performance was harmful, trivial, or beneficial were expressed as percentages, reflecting the following descriptors: 1%, almost certainly not; 1–5%, very unlikely; 5–25%, unlikely; 25–75%, possibly; 75–95% likely; 95–99%, very likely; 0.99%, almost certainly44.

Ethics declarations

The Ethics Committee of the Faculty of Sport and Physical Education, University of Niš, Serbia, obtained ethical review and approval. The experimental procedures reported in this study were performed following the ethical standards of the Declaration of Helsinki, and the participants and their parents signed informed consent forms.

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