Swimming start performance (SS) is an important component of the swimming race, especially in short events (8). It consists of explosive movements intended to propel a swimmer from the starting block into the water (9,42). Among male elite swimmers, swimming velocities are on the order of 1.8–2 m·s−1, whereas typical average velocities over the first 15 m of the race are approximately 3 m·s−1 (8,12).
Many studies have shown improvements in the execution of sporting performances after warming up (3,6,7,25,31). However, a method called postactivation potentiation (PAP) has recently received considerable attention (15,19,34,35,41). Postactivation potentiation improves muscle contractility, strength, and speed in sporting performances by applying maximal or submaximal loads on the muscle before the performance. The effects observed with PAP are the result of a physiologic alteration that renders actin-myosin myofibril more sensitive to Ca2+, released from the sarcoplasmic reticulum, and an increase in muscle fiber recruitment, due to an intensification of the motor-neuron's excitation. This leads to an amplification of the muscle action potential, which improves the mechanical power and, consequently, the athletic performance (15,19,34,35,41).
Postactivation potentiation has been shown to be more effective in lower limbs when a rest period of 8 minutes is included after a submaximal stimulus application (24,29,39) because the optimum performance occurs when the fatigue has dissipated and the enhancement still exists (39); when it is applied to trained subjects or individuals with a high proportion of fast fibers (16,19,30,33,34,43); and when the PAP movement is biomechanically similar to the real movement (16,35). The use of the new Olympic OSB11 block (OMEGA, Zurich, Switzerland), which consists of a rear plate where swimmers can push with the rear foot, should therefore be considered when choosing an optimal activation exercise that is biomechanically similar to this movement (1,13,38).
Few studies to date have examined the SS performance using different types of warm-up, and those that exist were conducted without a specific stimulus to the lower limbs of the subjects (3,9,24). Moreover, no studies have been conducted to assess the effects of warm-ups on SS performance from the new block, where the legs have an asymmetric placement. Thus, there is an urgent need to identify asymmetric potentiation exercises that can provide a stronger and more specific stimulus. The lunge exercise, for example, primarily activates the hip and knee extensor muscles of the front leg (11,21) and, in track starts, causes the biggest impulse (20). The flywheel inertial device, YoYo squat (YoYo Technology AB, Stockholm, Sweden), however, draws on inertial systems to induce potentiation and, as has been reported in many EMG studies, leads to very high muscular activation (11,25–27,42). A potential benefit of flywheel inertial devices is that the resistance is independent of gravity. As such, the resistance can be applied from any direction, allowing for a wide variety of exercises (11,26–28,42). Because it is necessary be attached to a belt that emerges directly from the device, potentiation movements can also be applied with almost the same forward extension movement that the swimmer must perform on the block, thus avoiding falls.
The aim of this study was to compare the effects of 2 activation protocols for lower limbs on the variables that affect the swimming start. Two warm-up protocols were tested for induction of PAP: the lunge exercise, with maximum repetitions, and the YoYo squat flywheel inertial device, with maximum repetitions. These 2 protocols were compared with a standard warm-up (SWU) protocol. We hypothesized that PAP inducement using the flywheel inertial device would be the most appropriate warm-up for optimal performance in a swimming start.
Experimental Approach to the Problem
A repeated measures counterbalanced design was used in which swimmers performed 2 different activation protocols before performing an SS, after 8 minutes of rest. As a control, all participants first performed an SS after a SWU, which consisted of a varied swimming warm-up followed by dynamic lower limb stretching. Swimmers were then randomly separated into 2 groups. The first group performed the first activation protocol: Lunge Warm Up (LWU), which consisted of completion of a SWU followed by PAP inducement with 1 set of 3 lunge repetitions at 85% 1 repetition maximum (1RM). The second group performed the YoYo squat activation protocol (YWU), which consisted of completion of a SWU followed by PAP inducement with 1 set of 4 repetitions at maximal voluntary contraction on the YoYo squat flywheel device. The 4 repetitions on the YoYo squat flywheel device are necessary because the first repetition serves to charge the flywheel. To avoid a “fatigue/learning” effect, the group order was reversed in later tests. Three tests were carried out with 1-hour break between each.
Before the study, each participant was pretested in the pool with a timed 15-m swim, visited the laboratory to become familiar with the testing methods, and had their 3RM lunge measured (values = 77.1 ± 23.4 kg). During these sessions, swimmers also practiced the characteristic forward extension movement of the SS performance on the flywheel inertial device.
Fourteen trained swimmers (10 men and 4 women; height 176.3 ± 9.1 cm; weight 69 ± 11.4 kg) volunteered to take part in this study after being informed of all risks, discomforts, and benefits involved. All volunteers, from whom written informed consent and parental approval had been obtained, were members of swimming clubs in Granada (Spain), between the ages of 17 and 23 and federated swimmers with at least 5 years of participation in national competitions. The university ethics committee approved the study.
Before data collection, all subjects attended 3 training sessions on the YoYo squat flywheel inertial device. In these sessions, the RM values for the lunge were also obtained using a Multipower device (Technogym, Barcelona, Spain) according to the guidelines set by National Strength and Conditioning Association (21). In these sessions, swimmers also gave their informed consent and basic anthropometric measures were taken. These training sessions were conducted in the Physical Education and Sports Department, University of Granada (Spain), which is equipped with a Multipower device (Technogym). The experimental setting was the Olympic pool at the High Altitude Training Center, National Sports Council (Sierra Nevada) in the city of Pradollano, (Granada, Spain), which is equipped with the OSB11 block (OMEGA) and the flywheel inertial device (YoYo Technology AB), in the biomechanics laboratory.
Swimmers reported to the experimental setting on the morning of testing after having refrained from alcohol, caffeine, and strenuous exercise for the previous 48 hours. In the morning, between 9:00 and 15:00, after a standardized meal and fluid intake, swimmers performed 3 warm-ups with an hour break between each of them. Swimmers were allowed to drink water during the entire session.
Reference points were marked on the joints of the hip, knee, and ankle of swimmers on arrival. The swimmers were informed about the testing day procedures. Each time the swimmers completed a warm-up protocol, they had a rest period of 8 minutes after which they performed a competition SS at maximum speed. There was only 1 performance for each test to simulate the conditions of a competition “attempt” (FINA rules). During the entire session, there was an assistant who monitored the resting time for each subject. The starting signal was an auditory stimulus, in this case, the one usually used in competitions. In each trial, the subject was requested to mount the block. When in position, the subject was given the verbal command “take your mark,” and shortly afterward, the starting signal was sounded. After recording the trial, swimmers rested for an hour.
All swimmers first performed the SWU that included 400 m of varied swimming consisting of 200-m easy freestyle swim with 2 starts from the wall (one of them to get into the water and the other after 100 m); 1 × 50 m front crawl swim (12′5 fast/12′5 smooth); 1 × 50 m front crawl swim at race pace; and 100 m front crawl at a normal pace. To establish a sufficient time interval between one swimmer and the next, each swimmer began the warm-up when the previous swimmer was performing the second start of the first 200 m of the warm-up. After swimming, the participants began their dynamic stretching protocol, which consisted of forward leg swings, ankle dorsi- and plantar-flexion, side leg swings, high knees, heel flicks, squats, and lunges. Each exercise was performed 10 times, and the entire set was repeated twice (1 set per minute). Dynamic stretches were designed to have an effect on the musculature most closely related to the jump performance. An independent researcher monitored the entire stretching set to ensure that the stretching exercises were performed properly and at the right pace during the 4 minutes. After 8 minutes of rest, the swimmers performed an SS.
Next, swimmers were randomly divided into 2 groups of 7 people each. The first group performed the warm-up with the lunge repetitions (LWU). This consisted of warming and dynamic stretching, as in the SWU, followed by the PAP stimulus that consisted of lunge exercises performed in a Multipower machine (Figure 1). The position of the exercise was monitored to ensure compliance with the rules of the National Strength and Conditioning Association (21). In the starting position, the rear knee was placed on a lifted surface 5 cm from the ground so that the leg and thigh formed a 90° angle, while the foot of the front leg was placed entirely on the ground so that this leg and thigh also formed a 90° angle. When this position was set, the leg extensions were performed. To ensure consistency in the positioning of the front leg, swimmers placed their legs in the same position that they used to perform the swimming starts. All swimmers performed 3 repetitions at maximum speed to 85% of 1RM. During the entire exercise, a study collaborator monitored the initial position and the specific loads of each subject. After 8 minutes of rest, swimmers performed a swim start. The second group performed the warm-up with repetitions in the YoYo squat flywheel device (YWU). This consisted of warming up and dynamic stretching as in SWU, followed by the PAP stimulus that consisted of repetitions on the YoYo squat flywheel device (Figure 2). The starting position modeled the position used by the swimmers on the block in a swimming start performance, with the same front and rear placement of the legs. After attachment of the belt, swimmers performed 4 maximum intensity repetitions, with the first repetition serving to charge the flywheel. During the entire exercise, a study collaborator monitored the initial position and provided swimmers with device harnesses. After 8 minutes of rest, the swimmers performed an SS.
The third trial was carried out in the reverse order. The first group performed the YWU activation protocol and the second group performed the LWU activation protocol. After 8 minutes of rest, swimmers performed an SS.
Dive Distance (DD): The distance from the swimming pool wall, under the starting block, to the first contact of the swimmer's fingers with the water (in meters) (22).
Flight time (FT): The time between the last contact of the feet with the starting block and the first finger contact with water (in seconds) (22).
Mean Horizontal Hip Velocity (V × H): The horizontal hip distance during the flight, from the last contact of the feet with the starting block to the first finger contact with water, divided by the time elapsed for this action (in meter per second) (2).
Time to 5 m (T5 m): The time elapsed from when the strobe light flashed until the head arrived at the vertical 5-m line (in seconds) (2).
Time to 15 m (T15 m): The time elapsed from when the strobe light flashed until the head arrived at the vertical 15-m line (in seconds) (2).
Angle of Takeoff (AT): The angle between the horizontal line and the line that connects the body's center of mass with the reference spot on the foot, at the moment of the last contact of the foot with the starting block (in degrees) (36).
Angle of Entry (AE): The angle between the horizontal line and the line that connects the body's center of mass with the reference spot on the hand, at the moment of the first contact of the fingers with the water (in degrees) (36).
Block Time (BT): The time elapsed from when the strobe light flashed until the moment that the swimmer was separated from the block (in seconds).
Mean Angular Velocity of Knee Extension (VωK): The knee's angular difference between the moment of maximum extension and the moment of maximum flexion (“ready”), divided by the time elapsed for the performance of that extension (in radian per second).
Data Collection for Swim Starts
Each trial was recorded with 4 digital video cameras. One camera was a high-speed camera (HS Camera 300 Hz; Casio, Tokyo, Japan) that operated at a sampling rate of 300 Hz. This camera, which was mounted on a tripod and focused on the block, recorded the BT, AT, and VωK. The 3 other digital video cameras (Sony Video Camera, 50 Hz) were focused on the poolside. One of them recorded the block phase, another one recorded the underwater phase to 5 m and the last one recorded the swim phase to 15 m. These 3 sequences were overlapped in space and time by a video switcher (Digital Video Switcher SE-900, Whittier, USA). These cameras also recorded the DD, FT, V × H, AE, T5 m, and T15 m. The shutter speed was adjusted using a modality (Sport Mode) that maximized the shutter speed within the limits of the cameras being used (1/4,000 seconds), thereby minimizing any distortion within the movement of the swimmers. Both block cameras were focused on the starting system to detect the light emitted by the starting signal. The starting system (Signal Frame, Sportmetrics) simultaneously emitted an audible signal and a strobe flash; this was used to synchronize the starting signal with the video image. All video files were analyzed by 2 different researchers with the Kinovea (version 0.7.10.) software, which allowed for the analysis of the reference points drawn on the swimmers.
Statistical analysis was performed using SPSS (version 21.0; IBM, Chicago, IL, USA). Descriptive statistics of the data were expressed as the mean ± SD and the 95% confidence interval (CI). The test-retest reliability (intraclass correlation coefficient [ICC]), within and between observers, was analyzed for each of the variables.
After testing for the normality distribution, the analysis was carried out using a repeated measures ANOVA to determine the differences in SS performance within and between the subjects, after warm up with the 3 protocols. To detect differences between protocols, significance was accepted at the alpha < 0.05 level and paired comparisons were used in conjunction with Holm's Bonferroni method to control for type 1 errors.
To assess the reliability of the digitizing process (intraobserver and interobserver), 6 trials were quantified using intraclass correlation coefficients (ICC), 3 of them were digitized by the researcher and the other 3 by an investigator with experience in the Kinovea software digitization management. These correlations were calculated separately, for the repeated measures of all the variables, from 6 randomly chosen subjects. The intraobserver ICC ranged from 0.97 (95% CI, 0.96–0.98) to 0.99 (95% CI, 0.98–0.99); and the interobserver ICC ranged from 0.98 (95% CI, 0.97–0.98) to 0.99 (95% CI, 0.98–0.99). These results show a high correlation and reliability.
Mean, SD, and CI for all variables studied are summarized in Table 1.
The repeated measures ANOVA analysis revealed significant differences for DD (F2,12 = 35.861, p < 0.001) between the 3 warm-up protocols, and DD was highly significant after protocols with PAP inducement (p < 0.01) compared with the control. The distance to entry in the water was longer for YWU (304.28 ± 9.066 cm) and LWU (300.29 ± 8.654 cm) compared with SWU (294.2 ± 8.679 cm).
Significant differences in FT were also observed (F2,12 = 69.491, p < 0.001) after YWU compared with SWU (p < 0.001) and after YWU compared with LWU (p < 0.01). Mean times for YWU (0.28 ± 0.13 seconds) and LWU (0.31 ± 0.14 seconds) were shorter compared with SWU (0.33 ± 0.14 seconds).
The mean values recorded for V × H (during flight) were significantly different between the 3 warm-up protocols (F2,12 = 47.042, p < 0.001). Swimmers were faster during flight after the YWU activation protocol (4.89 ± 0.12 m·s−1) compared with the other 2 protocols (Table 1). The V × H was also significantly higher (p < 0.001) after LWU (4.15 ± 0.122 m·s−1) compared with SWU (3.63 ± 0.11 m·s−1).
The T5 m was significantly different between the 3 warm-up protocols (F2,12 = 24.453, p < 0.001; YWU and LWU, p < 0.001; SWU, p ≤ 0.001), where the mean time was shorter for YWU (1.65 ± 0.052 seconds) compared with LWU (1.71 ± 0.053 seconds) and both were shorter when compared with SWU (1.75 ± 0.057 seconds). LWU was significantly shorter compared with SWU (p = 0.03). In contrast, for T15 m, only YWU and SWU were significantly different (F2,12 = 4.262, p < 0.04), with mean values of 7.54 ± 0.23 seconds after SWU and 7.36 ± 0.22 seconds after YWU (p ≤ 0.05).
No differences were found for AE (F2,12 = 0.246, p = not significant) and AT (F2,12 = 0.457, p = not significant) between the 3 warm-up protocols (Table 1).
Although differences were found for BT (F2,12 = 6.595, p ≤ 0.05), pair comparisons only revealed differences between SWU and YWU (p ≤ 0.05), with shorter mean values recorded after YWU (0.741 ± 0.022 seconds) compared with the mean values recorded after SWU (0.792 ± 0.019 seconds).
Statistical analysis for VωK revealed significant differences between protocols (F2,12 = 23.286, p < 0.001). Mean values recorded after execution of the flywheel device (YWU) were significantly different compared with both SWU (p < 0.005) and LWU (p < 0.001). The mean knee extension velocity was the highest for YWU (107.41 ± 4.89 rad·s−1) in comparison with the 2 other warm-up protocols (Table 1).
The aim of this investigation was to compare the effects of 2 activation protocols for lower limbs on the variables that affect swimming start performance. Two specific ways of inducing PAP during the warm-up were studied: 3 maximum repetitions in a lunge exercise and 4 maximum repetitions in a YoYo squat flywheel inertial device. These 2 methods were compared with an SWU method. We hypothesized that an activation protocol that induced PAP using the flywheel inertial device would be the most appropriate warm-up for an optimal performance in a swimming start, and our results demonstrated that, indeed, YMU had the greatest enhancement on swimming start performance.
To improve SS, 2 activation protocols were added to the SWU. This activation should be applied to the lower limbs because, according to several studies in elite swimmers (5,18,36,44), there is a clear relationship between the propulsive actions of the legs and a good SS performance. The first protocol (SWU), which was established as the control, consisted of varied swimming, followed by dynamic lower limb stretching. This protocol was based on the performance improvement after physical warming that was previously shown by many authors (3,6,7,25,31) and on the demonstration that dynamic stretching protocols can improve the range of motion and explosive executions in swimmers (4,10,31,35,39). We decided to combine both aspects, physical warming and dynamic stretching, to provide specific stimuli and, thereby, enhance the effects achieved during warm-up as previously reported by Fletcher (17) and Samson (35).
In the LWU, the swimmers performed the same warm-up as in the SWU, which was then followed by PAP induction through a lunge repetition performed at 85% of 1RM. This protocol was based on the study of Kilduff et al. (24), which compared the effects of a warm-up and an activation protocol, based on PAP, on swimming starts. In that study, the authors found similar results after both the warm-up and after PAP, but they did not investigate whether the addition of PAP to the warm-up would be able to potentiate the stimulus or, in contrast, generate fatigue, which could counteract or even exceed the potentiation. Till and Cooke (40), reported that their participants did not react to the PAP because they were not able to recover after the PAP stimulus. In this study, although the load was heavy enough to cause activation, the short rest time did not allow the fatigue to be dissipated. For this reason, both appropriate load and rest were considered in our study. In the study of Kilduff et al. (24), PAP was induced by the squat exercise at 87% of 1RM. In our study, however, PAP was induced by the lunge exercise to provide a stimulus to the lower limbs that was biomechanically similar to the movement used in the new starting blocks (16) and that also considered the benefits of the free weight exercises used in the study of Kilduff et al. (24). During the lunge exercise, the front leg is mainly potentiated because of the asymmetry of the leg placement (11). According to the asymmetry study of leg arrangement carried out by Hardt et al. (20), the front leg causes the greatest impulse in track start.
In the YWU, the swimmers performed the same warm-up as in the SWU, which was then followed by PAP induction through 4 repetitions on the YoYo squat. The application of this activation system was an innovative aspect of our study because we have not found any reference to its use in swimming. The use of the YoYo squat was based on 2 clear objectives (a) to take advantage of the characteristics of the system to provide an activation movement that was biomechanically identical to the real action (16), without a risk of falling and (b) to generate, during the first repetition of each set, a high lower limb activation, due to the high requirements of power and strength in the concentric and eccentric phases (11,26–28,42). In several studies, the load is applied in accordance with a previous test of RM. However, throughout the entire process, subjects may vary their performance due to either a deterioration or an improvement in their skills or because the load was not obtained properly. This problem is resolved with the use of the YoYo squat because the resistance is proportional to the force applied. Hence, maximal performance can be achieved regardless of a subject's condition on the day of the test (11).
To assess the effectiveness of a swimming start, the analysis of the V × H is imperative because it accurately expresses the changes that occur in a swimmer's performance in distance, time, or both. We observed that V × H ostensibly improved after YWU (4.89 ± 0.12 m·s−1) compared with LWU and SWU (Table 1). This means that the swimmer's flight was longer and faster, as confirmed by the increased DD and the decreased FT (Table 1). There was also a significant improvement in these variables after LWU compared with SWU (V × H, p < 0.001; DD, p < 0.001; and FT, p = 0.004; Table 1). These results imply that activation protocols based on a PAP inducement can have positive effects on the participants during the first phases of the swimming start after takeoff. It is not possible to compare our results with those obtained by Kilduff et al. (24) because of differences in the activation protocols and variables recorded, such as horizontal and vertical peak forces recorded by Kilduff et al., which improved after PAP inducement. However, our results are clear evidence that an improvement in the peak forces occurred on the block. Several studies have reported that PAP inducement significantly improves peak forces because of the recruitment of fibers caused by maximal or submaximal voluntary muscular contractions (10,15,23,24,34,39,41). This leads to an increase in the velocity of the nerve fiber conduction and an increase in EMG activity. In explosive movements, such as jumping or an SS, this can lead to an increase in the height or distance, and jumping power. These results are in agreement with those obtained by Breed and Young (9), who assessed the effects of a specific resistance training that focused on SS and found that the improvement in the strength applied to the block was correlated with the improvement in the hip velocity during flight (p ≤ 0.05).
T5 m was shorter after the YWU protocol compared with that recorded after the LWU and the SWU protocols (Table 1). There was also a slight difference (p ≤ 0.05) between the values obtained after the LWU protocol compared with the SWU protocol, indicating that the LWU protocol is more effective (Table 1). The reduction in the recorded time was caused by the enhanced flight phase, as discussed above (5). The potentiation in takeoff ensures that swimmers enter the water with higher velocity, which can be used in the initial underwater gliding.
The results for T15 m show that the time was slightly decreased after the YWU. This supports the results previously obtained by West et al. (44) and Seifert et al. (36), where the best SS, defined as the time to 15 m, was correlated with the strength and power in the subject's lower limbs, which enabled development of a higher velocity at takeoff. However, we observed significant differences only between the YWU and the SWU protocols (p < 0.045; Table 1); the differences between the LWU and the 2 others protocols were not significant. These results could be because swimming to 15 m depends on other technical aspects, such as the power of the initial strokes or the effectiveness of undulatory swimming. For example, in the study of Elipot et al. (14), swimmers began the underwater kicks as soon as possible to gain speed. However, this caused an increase in the drag and, consequently, a loss of velocity. Swimming to 15 m could, in addition, have generated a level of fatigue that was higher than the potentiation, (40) thus requiring more rest time. However, the load applied may have been insufficient. Future studies should clarify this matter. Our results, from the PAP induction to the free weight exercises, were similar to those obtained by Kilduf et al. (24), and although T15 m did not increase or worsen, there was no significant improvement after PAP induction with the lunge.
The mean values obtained for VωK and BT were better after the YWU protocol compared with the other 2 protocols. The results for VωK indicate a better performance after the YoYo squat warm-up protocol (YWU vs. SWU, p < 0.01; YWU vs. LWU, p ≤ 0.001) because of the higher velocity of the knee extension compared with the others protocols (Table 1), thus enabling the swimmers to leave the block earlier. These results are in agreement with those obtained by Yamauchi and Ishii (45), who studied the relationships between force-velocity and vertical jump after resistance training for lower limbs. They concluded that the improvements gained in vertical jump were caused by a higher extension velocity of the knee, which was a consequence of the improvement in the power generated. In our study, the block phase of the swimmers was better after YWU because they were able to combine a shorter time on the block with a higher force production (9). This combination could be because the back leg was also potentiated during the YoYo squat executions, and according to Arellano et al. (1), the back leg provides a larger impulse on the new OSB11 block. It is not clear why such low mean VωK values were recorded after LWU (Table 1). Vertical jumping has been commonly used to improve swimming starts, and studies have shown an improvement after vertical movements (5,9,32). However, a recent study by Rebutini et al. (32), where they found an improvement in the SS performance after a plyometric horizontal training but not after a plyometric vertical training, is consistent with our low VωK values after LWU. Rebutini et al. concluded that enhancements to SS performance were caused by an increase in the rate of force development by the hip and knee due to the specific training. This suggests that the enhancement of general muscle performance is not sufficient to enhance overall performance. Rather, training for a specific skill is critical to achieving that goal because it ensures the control and training of the essential resultant force vectors. However, it is possible that the initial angle of the front knee of the swimmer was suboptimal for the required force production. In the study by Slawson et al. (37), they showed that, in SS, the optimal knee angle of the front leg should be fixed between 135 and 145°. It is possible that our subjects started with a knee angle greater than 145°. The balance between fatigue and potentiation generated may be the key to this issue and should be investigated in the future.
We observed a reduction in the time on the block (decreased BT) after YWU (0.741 ± 0.022 seconds) compared with SWU (0.792 ± 0.019 seconds), which may explain the dramatic improvement in VωK that we also observed. After YWU, the swimmers left the block earlier because their leg extension was faster. The BT observed after LWU was not significantly different compared with the other 2 protocols (Table 1), although the mean values were not longer than those obtained after SWU. These results are consistent with those observed for VωK after LWU. Because there is no improvement in the velocity of the extension of the legs, there is no reduction in the time on the block.
Neither AE nor AT were altered after any protocol (Table 1). Consequently, we can conclude that the technical aspects remained unchanged, and improvements in performance can be explained by the effects of different warm-up or activation protocols on the swimmers and not by technical variations in the execution of the SS.
In conclusion, the warm-up protocols evaluated in this study, which included a specific PAP application, showed better results than the SWU. Specifically, the application of the flywheel inertial device (YWU) is the most appropriate warm-up for optimal performance in a swimming start because it can enhance SS and may be especially relevant in short events.
Our study is important and relevant for the application of a system that can be used in the field of aquatic sports to enhance explosive movements, such as swimming start performances, which have been shown to improve the overall performance of swimmers, especially in short events. The benefit of the YMU protocol on start time and the increase in angular velocity of the knees lead us to recommend this protocol before competition in short events. The optimum performance occurs when the fatigue has dissipated and the enhancement is still present; therefore, improving the resistance to fatigue is an important consideration for coaches because this will allow for greater enhancement of performance after PAP. Although adaptation of this protocol to meet competitive constraints needs to be resolved in the future, its ability to improve the power applied during the first pulling strokes is an important subject and should be studied further.
The authors would like to acknowledge all the swimmers who voluntarily participated in this study. To the research group: CTS-527: “Physical Activity and Sport in Aquatic Environment,” for all their support that has made this study possible. The authors would also like to acknowledge the “High Altitude Training Center, National Sport Council” in Prado Llano (Granada, Spain) for allowing this study to be carried out in their sport facilities and the participation of the Biomechanics Lab member Blanca de la Fuente y Javier Argüelles.
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