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The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers
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ORIGINAL ARTICLE
The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers Influence de la force maximale des muscles des membres supérieurs et inférieurs et du tronc sur la performance en natation de sprint chez les nageurs adolescents M. Keiner a,∗,b, D. Yaghobi b, A. Sander a,c, K. Wirth a, H. Hartmann a a
Institute of sport science, Johann Wolfgang Goethe-University, Frankfurt, Germany Swimming Federation of the State Lower Saxony, Hannover, Germany c German Luge and Bobsled Federation, Berchtesgaden, Germany b
Received 13 November 2014; accepted 7 May 2015
KEYWORDS 1RM; Swim sprint performance; Swim starts; Trunk strength
∗
Summary Objectives. — Strength and speed are 2 major factors that determine a swimmer’s sprint performance, especially swim sprint performance and swim starts. This study identified and examined variables that determine the influence of maximal strength performance on different swim performance styles and distances in trained adolescent swimmers. Equipment and methods. — Twenty-one regional swimmers (12 males and 9 females, 17.5 ± 2 years; mass: 69.5 ± 11.4 kg; height: 177.3 ± 10.1 cm) volunteered to take part in the present study. One-repetition-maximum (1RM) in the back squat, dead lift, bent-over row and sit-up were used to determine maximum strength. Squat jump (SJ) and countermovement jump (CMJ) were evaluated to determine speed-strength performance. Swim performances of 15 to 100 meters in freestyle, breaststroke and backstroke were measured in a 25-m indoor
Corresponding author. E-mail address: [email protected] (M. Keiner).
http://dx.doi.org/10.1016/j.scispo.2015.05.001 0765-1597/© 2015 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001
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M. Keiner et al. pool. Pearson correlation analysis was used to assess the relationships between strength and power variables and swim variables. Results. — Strong negative correlations between leg strength (1RM squat), speed-strength (SJ and CMJ) and swim performance were found in this investigation, especially for short distances (up to 25 m, r = −0.75 to −0.94, P < 0.05). Additionally, moderate to mostly strong correlations (r = −0.37 to −0.85, P < 0.05) were found between the strength tests of the upper extremities, and non-uniform correlations were found for the trunk strength test (r = −0.05 to −0.68) and swim performance. Conclusion. — The maximal strength parameters of the upper and lower extremities and maximal trunk strength are good predictors of performance in sprint swimming in trained adolescent swimmers in different disciplines. © 2015 Elsevier Masson SAS. All rights reserved.
MOTS CLÉS 1RM ; Natation ; Sprint ; Départs en natation ; Force du tronc
Résumé Objectifs. — La force et la vitesse sont les deux facteurs principaux qui déterminent les performances d’un nageur en sprint, ainsi que les départs en natation. Cette étude a pour but d’identifier les variables qui déterminent l’influence des performances maximales dans différents styles de nage et distances de natation chez les nageurs adolescents entraînés. Équipement et méthodes. — Vingt et un nageurs de niveau régional (12 masculins et 9 féminins, âgés de 17,5 ± 2 ans ; poids : 69,5 ± 11,4 kg ; taille : 177,3 ± 10,1 cm) se sont portés volontaires pour participer à la présente étude. La performance sur un test d’une répétition maximum (1RM) en squat, en tirage en position assise a été utilisée pour déterminer la force maximale. Un « squat jump » (SJ) et « countermovement jump » (CMJ) ont été utilisés pour évaluer les performances de type force-vitesse. Les performances de natation sur des distances de 15 m à 100 m en nage libre, brasse et dos ont été évaluées dans un bassin de 25 m. Une analyse de corrélation de type Pearson a été utilisée pour évaluer la relation entre les variables de force et de puissance et les variables de performance en natation. Résultats. — Des corrélations négatives significatives ont été observées entre la force des membres inférieurs, la performance en SJ et CMJ et les performances en natation, notamment pour les courtes distances (jusqu’à 25 m, r = −0,75 à −0,94, p < 0,05). Des corrélations modérées à fortes (r = −0,37 à −0,85, p < 0,05) ont également été constatées entre les valeurs de force des membres supérieurs et les performances en natation alors que ces corrélations sont non significatives ou faiblement significatives pour la force des muscles du tronc (r = −0,05 à −0,68). Conclusion. — Les paramètres de force maximale des membres supérieurs et inférieurs, ainsi que la force maximale des muscles du tronc constituent de bons indicateurs des performances de natation en sprint chez des nageurs adolescents entraînés. © 2015 Elsevier Masson SAS. Tous droits réservés.
1. Abbreviations 1RM SJ CMJ s kg m FS BS BackS
one-repetition-maximum squat jump countermovement jump seconds kilogram meter freestyle breaststroke backstroke
2. Introduction A small range between winning and losing was shown during the 2014 European Swimming Championships, especially in short distances. These tight margins in achieving success
emphasize that each athlete must optimize every aspect of the race. Start performance in swimming requires a combination of reaction time, vertical and horizontal force off the block, and low resistance during underwater gliding. Ruschel et al. [1] reported that flight distance is one variable that determine start performance (r = −0.48). Therefore, swimmers need to jump as far as possible during a block start and travel the maximum distance at the highest velocity to influence this important factor [2]. It is not surprising that Breed and Young [3] identified countermovement jump (CMJ) performance as significantly related to flight distance (r = 0.69—0.84). Some investigations demonstrated a strong relationship between maximal strength in squat and jump performances [4,5]. West et al. [6] also showed that lower body strength and power are significantly related to swim time of 15 m in international male swimmers (r = −0.66 to −0.74). Therefore, there may be an advantage of high maximum strength level in turning (pushes of the wall). Strength training or vertical jump training programs seem appealing because of their high correlation with start performance
Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001
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Strength predictors of swim performance in swimming, which may indicate that greater leg power and jumping ability would improve start performances and overall race times [7]. An increase in swimming speed may be accomplished from a biomechanical point of view in two ways: optimizing stroke frequency [8] or extending stroke length [9—11]. Higher-level swimmers also present higher efficiencies, which are expressed by higher stroke index values [8,12]. Therefore, an apparent trend exists between optimal stroke length and frequency. Stroke length and frequency benefit from a high level of maximal strength. The basic approach for increasing stroke length is the development of the maximum force possible, which increases the force maxima per single stroke. Strength training to increase stroke length increases the single impulse through the development of maximum strength. It also improves fatigue resistance by reducing the time period of a single impulse to the smallest possible time. Training to optimize stroke frequency also benefits from an accompanying strengthtraining plan to increase maximum strength levels. An increase in frequency (the number of impulses per unit of time) is expected in athletes with low maximum strength. Swimmers with increased maximum strength should maintain a certain frequency for longer periods of time, which contributes to an increase in impulse (frequency sum). The longer the distance, the less the pulse sum depends on maximum strength. Therefore, Hawley and Williams [13] and Smith et al. [14] demonstrated a strong relationship (r = 0.82 to 0.93) between upper body strength using peak torque and sprint swimming performance over 25 yards and 50 meters. Some studies reported that muscular strength correlated significantly with swim velocity [15], and upper body muscular strength output highly correlated with swim velocity over short swimming distances (r = 0.87) [13,14,16]. Additionally, longitudinal investigations demonstrated that an increase in strength level is beneficial for improving swim performance in water polo players and swimmers of different playing levels and ages [17—19]. All movements and forces of the extremities create high forces that act on the trunk, which is also true for swimming. The trunk muscles must control the extremities and transfer the forces to ensure efficient locomotion. Therefore, athletes are constantly transferring forces between the extremities, which require support from the musculature of the trunk to maintain the kinetic chain of the body intact. Therefore, trunk muscle strength may also be performance limiting. To our best knowledge, no study examined the associations between swimming performance and dynamic maximal trunk strength. Correlation analyses of different test protocols, trunk strengths and athletic performance measurements [20—28] and longitudinal studies of the effect of trunk muscle strength training on athletic performance [29—33] are found in the literature. These analyses generally show low to moderate correlations between trunk strength and athletic performance, with the exceptions of investigations of Dendas, Ikeda et al. and Iwai et al. [20,23—25]. In summary, strength and speed are 2 major factors that determine a swimmer’s sprint performance during training and competition, especially swim sprint performance and swim starts [19,34]. Therefore, this study identified and examined variables that determine the influence of maximal
3 strength performance on different swim performance styles and distances in trained adolescent swimmers.
3. Methods 3.1. Subjects Written informed consent was obtained from twenty-one regional swimmers (12 males and 9 females, 17.5 ± 2 years; mass: 69.5 ± 11.4 kg; height: 177.3 ± 10.1 cm) who volunteered to take part in the present study. Recruited subjects were all participants of the Youth German Championships or Northern German Championships. The study was performed at the end of May, two weeks after the seasonal highlight of the swimmers. Swimmers in the current study specialized in 50- and 100-m freestyle swimming. The subjects had little strength training experience. Subjects did not participate in fatiguing training sessions for a minimum of 2 days before testing. None of the participants reported any injuries at the time of testing. The same researchers collected anthropometric and performance measurements at the same time on testing day, and all participants were asked to wear the same clothing and footwear, for the strength test. All participants were asked to eat and drink a sufficient amount until 1 hour before testing. Each subject and their parents were informed of the experimental risks involved with the research. All subjects provided written informed consent to participate. Informed consent was also obtained from the subjects’ parents if the subjects were less than 18 years of age. The institutional review board approved the research design. The study was performed with respect to the use of human subjects in accordance with the Helsinki declaration.
3.2. Testing protocol The performance tests were evaluated on 3 testing days. Subjects were randomly divided into 5 groups (each with 4 or 5 subjects) to minimize the influential factor ‘‘order of the test days’’. All groups completed the tests in a different order (Table 1). Testing day 2 was completed 2 days after testing day 1 and testing day 3 was completed 2 days after testing day 2. All tests were performed after a standardized warm-up routine. Subjects had 10 minutes of active recovery between each start and a 1-hour break before the strength tests were performed. 3.2.1. Swim tests The evaluation process was conducted in a 25-m indoor swimming pool. Two trained subjects determined performance times using a chronometer (Schütt PC-90, Marburg, Germany), and the mean value of both measurements was obtained for each trial. All starts were performed from a standard poolside mounted starting block under simulated race conditions. The subject swam distances up to 25 m at a maximal sprint. Distances over 50 m were subsequently performed at optimal speed. For the block starts, subjects were instructed to mount the block, and they were given a verbal command ‘‘take your mark’’ when in position, which was shortly followed by the starting signal. Breaststrokepulling tests (pool-kick between the legs) at 15 m and 25 m and breaststroke-kick tests (with stretched out arms and a
Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001
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board in hands) at 25 m were started in the pool. Swimmers pushed themselves off from the wall, and the time was started when the feet of the subjects left the wall. A coach motivated and coached the swimmers at all times during the swim tests. The test-retest correlations of the swim tests were between r = 0.84 to r = 0.93 (Pearson; P < 0.05). 3.2.2. Strength tests The one-repetition-maximum (1RM) measurement is recommended for swimmers as an appropriate test to determine maximum strength during childhood and adolescence [6,35]. Therefore, swimmers participated in technique training for the strength tests twice weekly for 2 weeks before they were tested and completed a familiarization test. The warm-up was standardized and consisted of 2 sets with 6—8 repetitions using a submaximal weight. Strength tests were evaluated in a maximum of 5 trials. The 1RM in the back squat was used to determine the maximum strength of the lower extremities in the swimmers. The parallel (60◦ knee angle) version of the squat was performed. The test-retest correlation was r = 0.97 (Pearson; P < 0.05) for the back squat. The 1RM dead lift started with the bar on the floor and shoulder blades directly over the bar. The bar was kept close to the body while pulling until the hips and knees were locked. The hands were kept pronated, and the back was kept straight. The test-retest reliability of both pretest sessions constituted a r = 0.96 (Pearson; P < 0.05). For the bench press exercise, the bar was lowered to touch the chest gently at the level of the nipples and pushed up to arms’ length. Cheating by bouncing the bar on the chest in the eccentric-concentric transition phase was not allowed. The test-retest reliability of both pretest sessions constituted a r = 0.98 (Pearson; P < 0.05). For the 1RM in the bent-over row, the swimmers used both arms (close to the torso) to lift a barbell from the floor to the stomach in a bent-forward position (hip angle = 90◦ ). Subjects were instructed to bring the upper body into a horizontal position and to keep the knee almost stretched. The hands were kept pronated, and the back was kept straight. The test-retest reliability of both pretest sessions constituted a r = 0.92 (Pearson; P < 0.05). For the 1RM sit-up, swimmers started in an upright position (back straight) on an ab-bench. The feet were fixed. The subjects had a barbell on their shoulders (grip similar to the front squat), but the hands supported the weight. The subjects slowly lowered themselves, gently touched the bench with their shoulders and started pushing into an upright position (always keeping a straight back). The test-retest reliability of both pretest sessions constituted a r = 0.91 (Pearson; P < 0.05). 3.2.3. Jump performance The SJ is a vertical jump from a crouched position that is performed without using momentum (test-retest correlation, r = 0.87, Pearson, P < 0.05). The knees were bent to 90◦ , the body was upright, and the hands remained at the hips. The CMJ is a vertical jump that uses momentum (testretest correlation, r = 0.94, Pearson, P < 0.05). The jump was initiated from an upright position, and the center of the body was lowered until the knees were bent at a 90◦ angle. The
CMJ is a rapid movement with no pause between eccentric and concentric phases.
3.3. Statistical analysis Normality of the distribution was tested using the Kolmogorov-Smirnov test, and normally distributed data are expressed as the means ± standard deviation. Bivariate Pearson correlation analysis was used to assess the relationship between the strength and power variables and the swim variables. If the data were not normally distributed, relationships between the test variables were calculated using Spearman correlation coefficients. The significance level was set at P < 0.05. The relationships were classified as follows: 0 = no correlation, 0 < | r | < 0.2 = very weak correlation, 0.2 ≤ | r | < 0.4 = weak correlation, 0.4 ≤ | r | < 0.6 = moderate correlation, 0.6 ≤ | r | < 0.8 = strong correlation, 0.8 ≤ | r | < 1.0 = very strong correlation, 1 = perfect correlation.
4. Results All data were normally distributed. The subjects performed a mean of 73.1 ± 20.5 kg 1RM in the squat, 58.5 ± 20.0 kg in the bench press, 62.5 ± 18.2 kg in the bent-over row, 85.3 ± 27.2 kg in the dead lift and 22.3 ± 5.8 kg in the ab-bench. The subjects reached a mean of 32.8 ± 7.4 cm in the SJ and 34.7 ± 8.1 cm in the CMJ. The swimmers passed 15 m and 25 m in freestyle starting from the block in 7.38 ± 0.76 s and 13.65 ± 1.45 s, respectively. The swimmers passed 50 m and 100 m in freestyle after 30.08 ± 3.81 s and 68.39 ± 9.27 s, respectively. Swimmers finished the 15-m breaststroke-pulling test starting in the pool in 10.8 ± 1.3 s. Swimmers finished the 25-m breaststroke-kick and breaststroke-pulling in a mean time of 22.5 ± 3.3 s and 20.06 ± 2.36 s, respectively. The swimmers completed the 50-m and 100-m backstroke tests in 36.98 ± 4.72 s and 82.37 ± 12.50 s, respectively. The results of the correlation analysis are shown in Tables 2—4. The correlation coefficient between the 1RM dead lift and squat performance was r = 0.60 (P < 0.05). The correlation coefficient between the 1RM sit-up and squat performance was r = 0.60 (P < 0.05).
5. Discussion The present study examined the relationship between maximum strength variables and swim performances in trained swimmers. This study demonstrated that maximum strength of the upper and lower limbs and speed-strength performance of the lower body were strongly related to swim performance. Additionally, trunk strength was moderately to strongly related to swim performance. The strong correlations between leg strength (1RM squat), speed-strength (SJ and CMJ) and swim performance found in this investigation are not surprising, especially for the short distances tested (up to 25 m, r = 0.75—0.94), unless flight distance at the start is considered the dominant variable [1], even if our subjects comprised a heterogeneous group. Bishop et al. [36] identified in a review that a strong start accounts for 30% of a 50-m race, which suggests that a strong dive is essential to maximize performance. Cronin
Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001
Speed-strength Swim tests
Block 2
SJ 15 m freestyle 25 m freestyle 50 m freestyle 100 m freestyle 1RM squat
Strength tests
Block 3 CMJ 15 m breaststroke-pulling 50 m backstroke 100 m backstroke 1RM bent-over row 1RM dead lift
SJ: squat jump; CMJ: countermovement jump; m: meters; 1RM: one-repetition-maximum; 1RM sit-up: performance in sit-up.
Table 2
Correlations between lower limb performance and swimming performance. 15 m FS
25 m FS
50 m FS
100 m FS
BS-kick 25 m
BS-pulling 15 m
BS-pulling 25 m
50 m BS
100 m BS
50 m BackS
100 m BackS
−0.76* 0.58
−0.75* 0.56
−0.72* 0.52
−0.68* 0.46
−0.58* 0.33
−0.69* 0.48
−0.72* 0.52
−0.70* .049
−0.73* 0.53
−0.54* 0.29
−0.33* 0.11
r r2
−0.94* 0.88
−0.94* 0.88
−0.82* 0.67
−0.77* 0.59
−0.78* 0.61
−0.86* 0.74
−0.86* 0.74
−0.87* 0.76
−0.86* 0.74
−0.53* 0.28
−0.36* 0.13
CMJ r r2
−0.92* 0.85
−0.91* 0.83
−0.82* 0.67
−0.77* 0.59
−0.75* 0.56
−0.83* 0.69
−0.85* 0.72
−0.85* 0.72
−0.84* 0.71
−0.53* 0.28
−0.37* 0.14
Squat r r2 SJ
FS: freestyle; BS: breaststroke; BackS: backstroke; SJ: squat jump; CMJ: countermovement jump; m: meters; * P < 0.05.
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25 m breaststroke-kick 25 m breaststroke-pulling 50 m breaststroke 100 m breaststroke 1RM bench press 1RM sit-up
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Overview of performance test order.
Strength predictors of swim performance
Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001
Table 1
5
15 m FS
50 m FS
100 m FS
BS-kick 25 m
BS-pulling 15 m
BS-pulling 25 m
50 m BS
100 m BS
50 m BackS
100 m BackS
Bench press r −0.84* r2 0.71
−0.85* 0.72
−0.83* 0.69
−0.81* 0.66
−0.68* 0.46
−0,85* 0.72
−0.81* 0.66
−0.79* 0.62
−0.82* 0.67
−0.65* 0.42
−0.37* 0.14
Bent-over row r −0.81* 2 r 0.66
−0.83* 0.69
−0.80* 0.64
−0.77* 0.59
−0.70* 0.49
−0.86* 0.74
−0.83* 0.69
−0.78* 0.61
−0.80* 0.64
−0.65* 0.42
−0.39* 0.15
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25 m FS
FS: freestyle; BS: breaststroke; BackS: backstroke; m: meters; * P < 0.05.
Table 4
Correlations between trunk performance and swimming performance. 15 m FS
25 m FS
50 m FS
100 m FS
BS-kick 25 m
BS-pulling 15 m
BS-pulling 25 m
50 m BS
100 m BS
50 m BackS
100 m BackS
Dead lift r −0.68* 2 r 0.46
−0.68* 0.46
−0.68* 0.46
−0.64* 0.41
−0.61* 0.37
−0.67* 0.45
−0.65* 0.42
−0.65* 0.42
−0.67* 0.45
−0.51* 0.26
−0.20 0.04
Ab-bench −0.51* r r2 0.26
−0.42 0.18
−0.48* 0.23
−0.38* 0.14
−0.26* 0.07
−0.30* 0.09
−0.30* 0.09
−0.39* 0.15
−0.38* 0.14
−0.31* 0.10
−0.05 0.00
M. Keiner et al.
FS: freestyle; BS: breaststroke; BackS: backstroke; m: meters; * P < 0.05.
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Correlations between upper body performance and swimming performance.
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Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001
Table 3
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Strength predictors of swim performance et al. [37] demonstrated that faster swimmers with better speed-strength performance had faster turn velocities, and speed-strength performances explained 19 percent of the turn performance. For example, a swimmer has 1 block start and 3 turns (pushes of the wall) in a 100-m FS performance in a 25-m pool. This arrangement may be one argument for our other findings of strong correlations between leg strength and speed-strength for distances over 25 m. The moderate to mostly strong correlations of the strength tests of the upper extremities and swim performance also show the importance of maximal strength for short distance swimmers, not only for start performance. Therefore, it can be assumed that swimmers with high maximum strength have the advantage of a high single impulse. This relationship is relevant for performance of the legs and upper extremities in the BS and other swim styles up to 100 m. The results of this investigation are consistent with the results of West et al. [6], Hawley et al. [13,38], Garrido et al. [39] and Breed and Young [3]. However, West et al. [6] evaluated better performance parameters, which may be explained by subject selection. The subjects in West et al.’s study [6] were members of the British Sprint Development squad, and they were currently engaged in a structured weight-training program for 2 years before the start of the study. The heterogeneous performance of the tested participants in this study suggests that statistically higher correlations could be calculated. Therefore, the data of this investigation should be handled with caution when drawing conclusions for elite athletes. Nevertheless, our data show that maximum strength and speed-strength tests of the upper and lower extremities are 2 major factors that determine a swimmer’s sprint performance [6,19,34]. The 1RM in a parallel squat, bench press and bent-over row could be key performance tests in elite and [6] young athletes [35] provided that the technique is learned accurately under expert supervision. Therefore, our results may identify a test battery for sprint swimmers that could aid in the selection process for elite swim academies. The literature review on the relationship between maximal dynamic trunk strength performance and swimming performance revealed that no investigation previously analyzed these parameters. However, the data show a nonuniform direction of correlations between trunk strength and swim performance (r = −0.05 to −0.68). The data of this investigation demonstrated that the 1RM in the dead lift and sit-up were the correct tests designs to analyze trunk strength performance in the context of swimming. Most of the strength tests used in literature are strength isometric (e.g., McGill protocol [40]), dynamic (e.g., time sit-ups [41]) test protocols or core stability test protocols [42]. No isometric action of trunk muscles can be assumed in sport performance and swimming, just nearly isometric actions. Furthermore, it can be argued that trunk muscle endurance tests primarily activate slow-twitch muscle fibers because of the submaximal character of muscle actions, whereas strength and power tests involve both slow- and fast-twitch muscle fibers because of maximal activation levels. Therefore, our results indicate that dynamic maximal strength tests (sit-up, dead lift) may be good performance predictors for some sprint swim styles. Nevertheless, our data on the influence of trunk strength appeared to differentiate between swim styles (e.g., FS vs. BackS), but the reason for
7 this differentiation cannot be answered on the basis of our results. Notably, but not surprisingly, a strong correlation was observed between trunk strength (1RM sit up and 1RM dead lift) and squat performance. This is consistent with the observations of the researchers that in the determination of 1RM in squat of this population (low strength training experience), the limiting factor often seemed to be trunk strength. In summary, the maximal strength parameters of the upper and lower extremities and maximal trunk strength are good predictors of performance in sprint swimming in different disciplines. Therefore, the 1RM of the squat, bench press, bent-over row, dead lift and sit-up, and SJ and CMJ should be a part of the test battery for sprint swimmers in the weight room. Furthermore, these data imply that swimmers must incorporate lower and upper body strength and power training into their training schedule to improve the swim start, which is a key component of the overall sprint swimming performance. The squat, bench press, bent-over row, dead lift and sit-up are good training exercises for sprint swimmers to enhance their maximum strength in these exercises [18].
Disclosure of interest The authors declare that they have no conflicts of interest concerning this article.
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ORIGINAL ARTICLE
The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers Influence de la force maximale des muscles des membres supérieurs et inférieurs et du tronc sur la performance en natation de sprint chez les nageurs adolescents M. Keiner a,∗,b, D. Yaghobi b, A. Sander a,c, K. Wirth a, H. Hartmann a a
Institute of sport science, Johann Wolfgang Goethe-University, Frankfurt, Germany Swimming Federation of the State Lower Saxony, Hannover, Germany c German Luge and Bobsled Federation, Berchtesgaden, Germany b
Received 13 November 2014; accepted 7 May 2015
KEYWORDS 1RM; Swim sprint performance; Swim starts; Trunk strength
∗
Summary Objectives. — Strength and speed are 2 major factors that determine a swimmer’s sprint performance, especially swim sprint performance and swim starts. This study identified and examined variables that determine the influence of maximal strength performance on different swim performance styles and distances in trained adolescent swimmers. Equipment and methods. — Twenty-one regional swimmers (12 males and 9 females, 17.5 ± 2 years; mass: 69.5 ± 11.4 kg; height: 177.3 ± 10.1 cm) volunteered to take part in the present study. One-repetition-maximum (1RM) in the back squat, dead lift, bent-over row and sit-up were used to determine maximum strength. Squat jump (SJ) and countermovement jump (CMJ) were evaluated to determine speed-strength performance. Swim performances of 15 to 100 meters in freestyle, breaststroke and backstroke were measured in a 25-m indoor
Corresponding author. E-mail address: [email protected] (M. Keiner).
http://dx.doi.org/10.1016/j.scispo.2015.05.001 0765-1597/© 2015 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001
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M. Keiner et al. pool. Pearson correlation analysis was used to assess the relationships between strength and power variables and swim variables. Results. — Strong negative correlations between leg strength (1RM squat), speed-strength (SJ and CMJ) and swim performance were found in this investigation, especially for short distances (up to 25 m, r = −0.75 to −0.94, P < 0.05). Additionally, moderate to mostly strong correlations (r = −0.37 to −0.85, P < 0.05) were found between the strength tests of the upper extremities, and non-uniform correlations were found for the trunk strength test (r = −0.05 to −0.68) and swim performance. Conclusion. — The maximal strength parameters of the upper and lower extremities and maximal trunk strength are good predictors of performance in sprint swimming in trained adolescent swimmers in different disciplines. © 2015 Elsevier Masson SAS. All rights reserved.
MOTS CLÉS 1RM ; Natation ; Sprint ; Départs en natation ; Force du tronc
Résumé Objectifs. — La force et la vitesse sont les deux facteurs principaux qui déterminent les performances d’un nageur en sprint, ainsi que les départs en natation. Cette étude a pour but d’identifier les variables qui déterminent l’influence des performances maximales dans différents styles de nage et distances de natation chez les nageurs adolescents entraînés. Équipement et méthodes. — Vingt et un nageurs de niveau régional (12 masculins et 9 féminins, âgés de 17,5 ± 2 ans ; poids : 69,5 ± 11,4 kg ; taille : 177,3 ± 10,1 cm) se sont portés volontaires pour participer à la présente étude. La performance sur un test d’une répétition maximum (1RM) en squat, en tirage en position assise a été utilisée pour déterminer la force maximale. Un « squat jump » (SJ) et « countermovement jump » (CMJ) ont été utilisés pour évaluer les performances de type force-vitesse. Les performances de natation sur des distances de 15 m à 100 m en nage libre, brasse et dos ont été évaluées dans un bassin de 25 m. Une analyse de corrélation de type Pearson a été utilisée pour évaluer la relation entre les variables de force et de puissance et les variables de performance en natation. Résultats. — Des corrélations négatives significatives ont été observées entre la force des membres inférieurs, la performance en SJ et CMJ et les performances en natation, notamment pour les courtes distances (jusqu’à 25 m, r = −0,75 à −0,94, p < 0,05). Des corrélations modérées à fortes (r = −0,37 à −0,85, p < 0,05) ont également été constatées entre les valeurs de force des membres supérieurs et les performances en natation alors que ces corrélations sont non significatives ou faiblement significatives pour la force des muscles du tronc (r = −0,05 à −0,68). Conclusion. — Les paramètres de force maximale des membres supérieurs et inférieurs, ainsi que la force maximale des muscles du tronc constituent de bons indicateurs des performances de natation en sprint chez des nageurs adolescents entraînés. © 2015 Elsevier Masson SAS. Tous droits réservés.
1. Abbreviations 1RM SJ CMJ s kg m FS BS BackS
one-repetition-maximum squat jump countermovement jump seconds kilogram meter freestyle breaststroke backstroke
2. Introduction A small range between winning and losing was shown during the 2014 European Swimming Championships, especially in short distances. These tight margins in achieving success
emphasize that each athlete must optimize every aspect of the race. Start performance in swimming requires a combination of reaction time, vertical and horizontal force off the block, and low resistance during underwater gliding. Ruschel et al. [1] reported that flight distance is one variable that determine start performance (r = −0.48). Therefore, swimmers need to jump as far as possible during a block start and travel the maximum distance at the highest velocity to influence this important factor [2]. It is not surprising that Breed and Young [3] identified countermovement jump (CMJ) performance as significantly related to flight distance (r = 0.69—0.84). Some investigations demonstrated a strong relationship between maximal strength in squat and jump performances [4,5]. West et al. [6] also showed that lower body strength and power are significantly related to swim time of 15 m in international male swimmers (r = −0.66 to −0.74). Therefore, there may be an advantage of high maximum strength level in turning (pushes of the wall). Strength training or vertical jump training programs seem appealing because of their high correlation with start performance
Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001
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Strength predictors of swim performance in swimming, which may indicate that greater leg power and jumping ability would improve start performances and overall race times [7]. An increase in swimming speed may be accomplished from a biomechanical point of view in two ways: optimizing stroke frequency [8] or extending stroke length [9—11]. Higher-level swimmers also present higher efficiencies, which are expressed by higher stroke index values [8,12]. Therefore, an apparent trend exists between optimal stroke length and frequency. Stroke length and frequency benefit from a high level of maximal strength. The basic approach for increasing stroke length is the development of the maximum force possible, which increases the force maxima per single stroke. Strength training to increase stroke length increases the single impulse through the development of maximum strength. It also improves fatigue resistance by reducing the time period of a single impulse to the smallest possible time. Training to optimize stroke frequency also benefits from an accompanying strengthtraining plan to increase maximum strength levels. An increase in frequency (the number of impulses per unit of time) is expected in athletes with low maximum strength. Swimmers with increased maximum strength should maintain a certain frequency for longer periods of time, which contributes to an increase in impulse (frequency sum). The longer the distance, the less the pulse sum depends on maximum strength. Therefore, Hawley and Williams [13] and Smith et al. [14] demonstrated a strong relationship (r = 0.82 to 0.93) between upper body strength using peak torque and sprint swimming performance over 25 yards and 50 meters. Some studies reported that muscular strength correlated significantly with swim velocity [15], and upper body muscular strength output highly correlated with swim velocity over short swimming distances (r = 0.87) [13,14,16]. Additionally, longitudinal investigations demonstrated that an increase in strength level is beneficial for improving swim performance in water polo players and swimmers of different playing levels and ages [17—19]. All movements and forces of the extremities create high forces that act on the trunk, which is also true for swimming. The trunk muscles must control the extremities and transfer the forces to ensure efficient locomotion. Therefore, athletes are constantly transferring forces between the extremities, which require support from the musculature of the trunk to maintain the kinetic chain of the body intact. Therefore, trunk muscle strength may also be performance limiting. To our best knowledge, no study examined the associations between swimming performance and dynamic maximal trunk strength. Correlation analyses of different test protocols, trunk strengths and athletic performance measurements [20—28] and longitudinal studies of the effect of trunk muscle strength training on athletic performance [29—33] are found in the literature. These analyses generally show low to moderate correlations between trunk strength and athletic performance, with the exceptions of investigations of Dendas, Ikeda et al. and Iwai et al. [20,23—25]. In summary, strength and speed are 2 major factors that determine a swimmer’s sprint performance during training and competition, especially swim sprint performance and swim starts [19,34]. Therefore, this study identified and examined variables that determine the influence of maximal
3 strength performance on different swim performance styles and distances in trained adolescent swimmers.
3. Methods 3.1. Subjects Written informed consent was obtained from twenty-one regional swimmers (12 males and 9 females, 17.5 ± 2 years; mass: 69.5 ± 11.4 kg; height: 177.3 ± 10.1 cm) who volunteered to take part in the present study. Recruited subjects were all participants of the Youth German Championships or Northern German Championships. The study was performed at the end of May, two weeks after the seasonal highlight of the swimmers. Swimmers in the current study specialized in 50- and 100-m freestyle swimming. The subjects had little strength training experience. Subjects did not participate in fatiguing training sessions for a minimum of 2 days before testing. None of the participants reported any injuries at the time of testing. The same researchers collected anthropometric and performance measurements at the same time on testing day, and all participants were asked to wear the same clothing and footwear, for the strength test. All participants were asked to eat and drink a sufficient amount until 1 hour before testing. Each subject and their parents were informed of the experimental risks involved with the research. All subjects provided written informed consent to participate. Informed consent was also obtained from the subjects’ parents if the subjects were less than 18 years of age. The institutional review board approved the research design. The study was performed with respect to the use of human subjects in accordance with the Helsinki declaration.
3.2. Testing protocol The performance tests were evaluated on 3 testing days. Subjects were randomly divided into 5 groups (each with 4 or 5 subjects) to minimize the influential factor ‘‘order of the test days’’. All groups completed the tests in a different order (Table 1). Testing day 2 was completed 2 days after testing day 1 and testing day 3 was completed 2 days after testing day 2. All tests were performed after a standardized warm-up routine. Subjects had 10 minutes of active recovery between each start and a 1-hour break before the strength tests were performed. 3.2.1. Swim tests The evaluation process was conducted in a 25-m indoor swimming pool. Two trained subjects determined performance times using a chronometer (Schütt PC-90, Marburg, Germany), and the mean value of both measurements was obtained for each trial. All starts were performed from a standard poolside mounted starting block under simulated race conditions. The subject swam distances up to 25 m at a maximal sprint. Distances over 50 m were subsequently performed at optimal speed. For the block starts, subjects were instructed to mount the block, and they were given a verbal command ‘‘take your mark’’ when in position, which was shortly followed by the starting signal. Breaststrokepulling tests (pool-kick between the legs) at 15 m and 25 m and breaststroke-kick tests (with stretched out arms and a
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board in hands) at 25 m were started in the pool. Swimmers pushed themselves off from the wall, and the time was started when the feet of the subjects left the wall. A coach motivated and coached the swimmers at all times during the swim tests. The test-retest correlations of the swim tests were between r = 0.84 to r = 0.93 (Pearson; P < 0.05). 3.2.2. Strength tests The one-repetition-maximum (1RM) measurement is recommended for swimmers as an appropriate test to determine maximum strength during childhood and adolescence [6,35]. Therefore, swimmers participated in technique training for the strength tests twice weekly for 2 weeks before they were tested and completed a familiarization test. The warm-up was standardized and consisted of 2 sets with 6—8 repetitions using a submaximal weight. Strength tests were evaluated in a maximum of 5 trials. The 1RM in the back squat was used to determine the maximum strength of the lower extremities in the swimmers. The parallel (60◦ knee angle) version of the squat was performed. The test-retest correlation was r = 0.97 (Pearson; P < 0.05) for the back squat. The 1RM dead lift started with the bar on the floor and shoulder blades directly over the bar. The bar was kept close to the body while pulling until the hips and knees were locked. The hands were kept pronated, and the back was kept straight. The test-retest reliability of both pretest sessions constituted a r = 0.96 (Pearson; P < 0.05). For the bench press exercise, the bar was lowered to touch the chest gently at the level of the nipples and pushed up to arms’ length. Cheating by bouncing the bar on the chest in the eccentric-concentric transition phase was not allowed. The test-retest reliability of both pretest sessions constituted a r = 0.98 (Pearson; P < 0.05). For the 1RM in the bent-over row, the swimmers used both arms (close to the torso) to lift a barbell from the floor to the stomach in a bent-forward position (hip angle = 90◦ ). Subjects were instructed to bring the upper body into a horizontal position and to keep the knee almost stretched. The hands were kept pronated, and the back was kept straight. The test-retest reliability of both pretest sessions constituted a r = 0.92 (Pearson; P < 0.05). For the 1RM sit-up, swimmers started in an upright position (back straight) on an ab-bench. The feet were fixed. The subjects had a barbell on their shoulders (grip similar to the front squat), but the hands supported the weight. The subjects slowly lowered themselves, gently touched the bench with their shoulders and started pushing into an upright position (always keeping a straight back). The test-retest reliability of both pretest sessions constituted a r = 0.91 (Pearson; P < 0.05). 3.2.3. Jump performance The SJ is a vertical jump from a crouched position that is performed without using momentum (test-retest correlation, r = 0.87, Pearson, P < 0.05). The knees were bent to 90◦ , the body was upright, and the hands remained at the hips. The CMJ is a vertical jump that uses momentum (testretest correlation, r = 0.94, Pearson, P < 0.05). The jump was initiated from an upright position, and the center of the body was lowered until the knees were bent at a 90◦ angle. The
CMJ is a rapid movement with no pause between eccentric and concentric phases.
3.3. Statistical analysis Normality of the distribution was tested using the Kolmogorov-Smirnov test, and normally distributed data are expressed as the means ± standard deviation. Bivariate Pearson correlation analysis was used to assess the relationship between the strength and power variables and the swim variables. If the data were not normally distributed, relationships between the test variables were calculated using Spearman correlation coefficients. The significance level was set at P < 0.05. The relationships were classified as follows: 0 = no correlation, 0 < | r | < 0.2 = very weak correlation, 0.2 ≤ | r | < 0.4 = weak correlation, 0.4 ≤ | r | < 0.6 = moderate correlation, 0.6 ≤ | r | < 0.8 = strong correlation, 0.8 ≤ | r | < 1.0 = very strong correlation, 1 = perfect correlation.
4. Results All data were normally distributed. The subjects performed a mean of 73.1 ± 20.5 kg 1RM in the squat, 58.5 ± 20.0 kg in the bench press, 62.5 ± 18.2 kg in the bent-over row, 85.3 ± 27.2 kg in the dead lift and 22.3 ± 5.8 kg in the ab-bench. The subjects reached a mean of 32.8 ± 7.4 cm in the SJ and 34.7 ± 8.1 cm in the CMJ. The swimmers passed 15 m and 25 m in freestyle starting from the block in 7.38 ± 0.76 s and 13.65 ± 1.45 s, respectively. The swimmers passed 50 m and 100 m in freestyle after 30.08 ± 3.81 s and 68.39 ± 9.27 s, respectively. Swimmers finished the 15-m breaststroke-pulling test starting in the pool in 10.8 ± 1.3 s. Swimmers finished the 25-m breaststroke-kick and breaststroke-pulling in a mean time of 22.5 ± 3.3 s and 20.06 ± 2.36 s, respectively. The swimmers completed the 50-m and 100-m backstroke tests in 36.98 ± 4.72 s and 82.37 ± 12.50 s, respectively. The results of the correlation analysis are shown in Tables 2—4. The correlation coefficient between the 1RM dead lift and squat performance was r = 0.60 (P < 0.05). The correlation coefficient between the 1RM sit-up and squat performance was r = 0.60 (P < 0.05).
5. Discussion The present study examined the relationship between maximum strength variables and swim performances in trained swimmers. This study demonstrated that maximum strength of the upper and lower limbs and speed-strength performance of the lower body were strongly related to swim performance. Additionally, trunk strength was moderately to strongly related to swim performance. The strong correlations between leg strength (1RM squat), speed-strength (SJ and CMJ) and swim performance found in this investigation are not surprising, especially for the short distances tested (up to 25 m, r = 0.75—0.94), unless flight distance at the start is considered the dominant variable [1], even if our subjects comprised a heterogeneous group. Bishop et al. [36] identified in a review that a strong start accounts for 30% of a 50-m race, which suggests that a strong dive is essential to maximize performance. Cronin
Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001
Speed-strength Swim tests
Block 2
SJ 15 m freestyle 25 m freestyle 50 m freestyle 100 m freestyle 1RM squat
Strength tests
Block 3 CMJ 15 m breaststroke-pulling 50 m backstroke 100 m backstroke 1RM bent-over row 1RM dead lift
SJ: squat jump; CMJ: countermovement jump; m: meters; 1RM: one-repetition-maximum; 1RM sit-up: performance in sit-up.
Table 2
Correlations between lower limb performance and swimming performance. 15 m FS
25 m FS
50 m FS
100 m FS
BS-kick 25 m
BS-pulling 15 m
BS-pulling 25 m
50 m BS
100 m BS
50 m BackS
100 m BackS
−0.76* 0.58
−0.75* 0.56
−0.72* 0.52
−0.68* 0.46
−0.58* 0.33
−0.69* 0.48
−0.72* 0.52
−0.70* .049
−0.73* 0.53
−0.54* 0.29
−0.33* 0.11
r r2
−0.94* 0.88
−0.94* 0.88
−0.82* 0.67
−0.77* 0.59
−0.78* 0.61
−0.86* 0.74
−0.86* 0.74
−0.87* 0.76
−0.86* 0.74
−0.53* 0.28
−0.36* 0.13
CMJ r r2
−0.92* 0.85
−0.91* 0.83
−0.82* 0.67
−0.77* 0.59
−0.75* 0.56
−0.83* 0.69
−0.85* 0.72
−0.85* 0.72
−0.84* 0.71
−0.53* 0.28
−0.37* 0.14
Squat r r2 SJ
FS: freestyle; BS: breaststroke; BackS: backstroke; SJ: squat jump; CMJ: countermovement jump; m: meters; * P < 0.05.
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Overview of performance test order.
Strength predictors of swim performance
Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001
Table 1
5
15 m FS
50 m FS
100 m FS
BS-kick 25 m
BS-pulling 15 m
BS-pulling 25 m
50 m BS
100 m BS
50 m BackS
100 m BackS
Bench press r −0.84* r2 0.71
−0.85* 0.72
−0.83* 0.69
−0.81* 0.66
−0.68* 0.46
−0,85* 0.72
−0.81* 0.66
−0.79* 0.62
−0.82* 0.67
−0.65* 0.42
−0.37* 0.14
Bent-over row r −0.81* 2 r 0.66
−0.83* 0.69
−0.80* 0.64
−0.77* 0.59
−0.70* 0.49
−0.86* 0.74
−0.83* 0.69
−0.78* 0.61
−0.80* 0.64
−0.65* 0.42
−0.39* 0.15
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25 m FS
FS: freestyle; BS: breaststroke; BackS: backstroke; m: meters; * P < 0.05.
Table 4
Correlations between trunk performance and swimming performance. 15 m FS
25 m FS
50 m FS
100 m FS
BS-kick 25 m
BS-pulling 15 m
BS-pulling 25 m
50 m BS
100 m BS
50 m BackS
100 m BackS
Dead lift r −0.68* 2 r 0.46
−0.68* 0.46
−0.68* 0.46
−0.64* 0.41
−0.61* 0.37
−0.67* 0.45
−0.65* 0.42
−0.65* 0.42
−0.67* 0.45
−0.51* 0.26
−0.20 0.04
Ab-bench −0.51* r r2 0.26
−0.42 0.18
−0.48* 0.23
−0.38* 0.14
−0.26* 0.07
−0.30* 0.09
−0.30* 0.09
−0.39* 0.15
−0.38* 0.14
−0.31* 0.10
−0.05 0.00
M. Keiner et al.
FS: freestyle; BS: breaststroke; BackS: backstroke; m: meters; * P < 0.05.
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Correlations between upper body performance and swimming performance.
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Table 3
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Strength predictors of swim performance et al. [37] demonstrated that faster swimmers with better speed-strength performance had faster turn velocities, and speed-strength performances explained 19 percent of the turn performance. For example, a swimmer has 1 block start and 3 turns (pushes of the wall) in a 100-m FS performance in a 25-m pool. This arrangement may be one argument for our other findings of strong correlations between leg strength and speed-strength for distances over 25 m. The moderate to mostly strong correlations of the strength tests of the upper extremities and swim performance also show the importance of maximal strength for short distance swimmers, not only for start performance. Therefore, it can be assumed that swimmers with high maximum strength have the advantage of a high single impulse. This relationship is relevant for performance of the legs and upper extremities in the BS and other swim styles up to 100 m. The results of this investigation are consistent with the results of West et al. [6], Hawley et al. [13,38], Garrido et al. [39] and Breed and Young [3]. However, West et al. [6] evaluated better performance parameters, which may be explained by subject selection. The subjects in West et al.’s study [6] were members of the British Sprint Development squad, and they were currently engaged in a structured weight-training program for 2 years before the start of the study. The heterogeneous performance of the tested participants in this study suggests that statistically higher correlations could be calculated. Therefore, the data of this investigation should be handled with caution when drawing conclusions for elite athletes. Nevertheless, our data show that maximum strength and speed-strength tests of the upper and lower extremities are 2 major factors that determine a swimmer’s sprint performance [6,19,34]. The 1RM in a parallel squat, bench press and bent-over row could be key performance tests in elite and [6] young athletes [35] provided that the technique is learned accurately under expert supervision. Therefore, our results may identify a test battery for sprint swimmers that could aid in the selection process for elite swim academies. The literature review on the relationship between maximal dynamic trunk strength performance and swimming performance revealed that no investigation previously analyzed these parameters. However, the data show a nonuniform direction of correlations between trunk strength and swim performance (r = −0.05 to −0.68). The data of this investigation demonstrated that the 1RM in the dead lift and sit-up were the correct tests designs to analyze trunk strength performance in the context of swimming. Most of the strength tests used in literature are strength isometric (e.g., McGill protocol [40]), dynamic (e.g., time sit-ups [41]) test protocols or core stability test protocols [42]. No isometric action of trunk muscles can be assumed in sport performance and swimming, just nearly isometric actions. Furthermore, it can be argued that trunk muscle endurance tests primarily activate slow-twitch muscle fibers because of the submaximal character of muscle actions, whereas strength and power tests involve both slow- and fast-twitch muscle fibers because of maximal activation levels. Therefore, our results indicate that dynamic maximal strength tests (sit-up, dead lift) may be good performance predictors for some sprint swim styles. Nevertheless, our data on the influence of trunk strength appeared to differentiate between swim styles (e.g., FS vs. BackS), but the reason for
7 this differentiation cannot be answered on the basis of our results. Notably, but not surprisingly, a strong correlation was observed between trunk strength (1RM sit up and 1RM dead lift) and squat performance. This is consistent with the observations of the researchers that in the determination of 1RM in squat of this population (low strength training experience), the limiting factor often seemed to be trunk strength. In summary, the maximal strength parameters of the upper and lower extremities and maximal trunk strength are good predictors of performance in sprint swimming in different disciplines. Therefore, the 1RM of the squat, bench press, bent-over row, dead lift and sit-up, and SJ and CMJ should be a part of the test battery for sprint swimmers in the weight room. Furthermore, these data imply that swimmers must incorporate lower and upper body strength and power training into their training schedule to improve the swim start, which is a key component of the overall sprint swimming performance. The squat, bench press, bent-over row, dead lift and sit-up are good training exercises for sprint swimmers to enhance their maximum strength in these exercises [18].
Disclosure of interest The authors declare that they have no conflicts of interest concerning this article.
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Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001
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Please cite this article in press as: Keiner M, et al. The influence of maximal strength performance of upper and lower extremities and trunk muscles on different sprint swim performances in adolescent swimmers. Sci sports (2015), http://dx.doi.org/10.1016/j.scispo.2015.05.001