effect of 4 months of training on aerobic power ...

EFFECT OF 4 MONTHS OF TRAINING ON AEROBIC POWER, STRENGTH, AND ACCELERATION IN TWO UNDER-19 SOCCER TEAMS MANUEL LO´PEZ-SEGOVIA,1 JOSE´ M. PALAO ANDRE´S,2

AND

JUAN J. GONZA´LEZ-BADILLO3

1

Research Section Soccer Federation of the Region of Murcia, Murcia, Spain; 2Department of Physical Activity and Sport Sciences, Catholic University San Antonio, Murcia, Spain; and 3Faculty of Sport, Pablo de Olavide University, Seville, Spain

ABSTRACT Lo´pez-Segovia, M, Palao Andre´s, JM, and Gonza´lez-Badillo, JJ. Effect of 4 months of training on aerobic power, strength, and acceleration in two under-19 soccer teams. J Strength Cond Res 24(10): 2705–2714, 2010—The purpose of this study was to assess the effect of the training executed by 2 under-19 teams from the first Spanish division on aerobic power, strength, and acceleration capacity. Two under-19 soccer teams that competed in the same league were evaluated on 2 occasions. The first evaluation (E1) was done at the beginning of the competitive period, and the second evaluation (E2) was done 16 weeks later, coinciding with the end of the first half of the regular season. The following were evaluated: lower-body strength through jump height with countermovement with and without load (CMJ/CMJ20), speed of the Smith machine bar movement in a progressive load test of full squats (FSL), acceleration capacity in 10, 20, and 30 m (T10, T20, T30, T10–20, T10–30, T20–30), and maximal aerobic speed (MAS). Team A executed complementary strength training, and training loads were determined with regard to the speed with which each player moved the bar in FSL. Between the evaluations, the training sessions of each team were recorded to assess their influence on the changes in E2. Team A significantly improved its MAS (p , 0.01) and its application of strength in the CMJ20 (p , 0.05) and FS20–30–40 (p , 0.01), while significantly worsening their acceleration capacity in all the splits (p , 0.01). Team B slightly worsened its MAS and significantly improved its application of strength in the CMJ20 (p , 0.01) and FS50–60 (p , 0.05). Its acceleration capacity improved insignificantly except for in the 20- to 30-m interval/T20–30 (p , 0.05). The present study demonstrates that the use of loads as a function of the speed of movement, without the need to determine maximum repetitions

Address correspondence to Lo´pez-Segovia M, manlopezsegovia@ hotmail.com. 24(10)/2705–2714 Journal of Strength and Conditioning Research ! 2010 National Strength and Conditioning Association

is a methodology that is adequate for the improvement of the application of strength in under-19 soccer players.

KEY WORDS concurrent training, performance, physical capacities, test, team sport

INTRODUCTION

S

occer is a sport that is characterized by the high presence of intermittent efforts during the 90 minutes that the match lasts (3,6,15,27,33,35). This has been the conclusion drawn from various research studies that try to clarify the physical and physiological requirements of this sport. These studies focus on (a) the study of mechanical variables such as the distance covered, the number of actions taken with the ball, or the speed of movement; and (b) the study of different physiological variables such as heart rate, maximal oxygen consumption, and the production of metabolites such as lactate or ammonium. Through the analysis of these variables, and from descriptive studies about the capacity for performance in soccer players (28,31,42), researchers have tried to establish a profile of physical requirements that determine the level of physical conditioning necessary for players to face the competition in the best possible conditions. Within this profile of physical performance, aerobic power is presented as an essential quality. This is because there is an important relationship between maximal oxygen consumption and the distance covered, the number of sprints completed, and the number of direct interventions made with the ball (2,4,15,38,45). In the aerobic context of the 90-minute match, strength is also an essential capacity for the soccer player to execute the constant muscular adjustments for the different actions (17). This capacity is decisive in players’ performance, and it is a variable that allows one to differentiate the performance when comparing players of different categories (1,9,41,45). This variable is normally evaluated in soccer players through different methodologies (e.g., isokinetic, jump test, and application of force on external loads). This makes comparing published data difficult. Isokinetic evaluations of strength have been used in soccer players (9,21,29), but they VOLUME 24 | NUMBER 10 | OCTOBER 2010 |

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Aerobic Power, Strength, and Acceleration have the disadvantage of being executed in unnatural movements and their measurement is carried out on isolated actions of the musculature. Therefore, the results are not very applicable to more complete actions (20). Still, a relationship between relative knee extensor torque at 240"s21 and acceleration capacity in 10 m has been found (r = 20.714, p , 0.01) (28). Different jump tests have also been employed for the evaluation of strength in soccer players (14,15,25,30, 36,39,40,44). A relationship has been found between jump capacity and acceleration capacity in soccer players (r = 0.72, p , 0.001) (44), and in the changes produced after training in both variables (r = 0.92, p , 0.01) (14). Differences were also found between players of different categories in jump capacity (1,12,41). The evaluation of the application of force on external loads has been used on few occasions (14,36,37,44,45). The choice of squats for these evaluations has been based on the relationship (44) between a maximal repetition in this exercise and the acceleration capacity over 10 m (r = 0.94), 10 m fly (r = 0.68), 20 m (r = 0.71), and vertical jump (r = 0.78). Studies about the changes or interventions on aerobic performance of Under-19 players are numerous (7,8,11,13, 15,25,32). However, the interventions done to assess the capacity for force production have been done almost entirely on professional players (1,9,44,45). The studies done with Under-19 players have focused on the study of the capacity for jumping and for accelerating different distances (7,11,14,15,19,21,25,34,37), but data have not been found about the application of strength in squats against external resistances. Likewise, no studies were found with Under-19 players that analyze the effect of training in 2 teams with the same competitive demands on their physical performance. Only one study was found about monitoring the effect of the different types of strength training in this age group (case study) (14). Currently, in soccer, there is a tendency for coaches to work on the physical capacities during field training as opposed to working on technical and tactical aspects during field training and physical capacities outside of field sessions. Therefore, the purpose of this study was to assess the effect of the training executed by 2 under-19 teams from the first Spanish division on strength, acceleration capacity, and aerobic power.

METHODS Experimental Approach to the Problem

Two under-19 soccer teams belonging to the first Spanish division participated in the study. Both teams executed a battery of tests for the evaluation of their performance at the end of the preseason, after at least 4 weeks of practice, and a posttest after the first half of the regular season, which was after 16 matches. A quasiexperimental design with a pretest and a posttest was used. The independent variable was the training variable executed by the teams (team A, 4 field sessions and 2 resistance training sessions; and team B, 3–4 field sessions). The dependent variables were jump height in

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countermovement jump with and without load (CMJ/CMJ20), speed of the Smith machine bar movement in a progressive load test of full squats (FSL), acceleration capacity in 10, 20, and 30 m (T10, T20, T30, T10–20, T10–30, T20–30), and maximal aerobic speed (MAS). Subjects

Thirty-seven under-19 soccer field players belonging to 2 teams (team A, n = 19; team B, n = 18) voluntarily participated in this study. Of these players, only the data from those that took part in both evaluations were analyzed. The mean (6SD) age, weight, and height of those in the 2 teams were 18.43 (60.6) years, 73.8 (68.1) kg, and 178.92 (67.9) cm for team A, and 18.08 (60.8) years, 69.9 (66.6) kg, and 175.45 (64.9) cm for team B. The 2 teams competed in the under-19 Spanish first division. The study was approved by the Research Ethics Committee beforehand. The subjects received information about the characteristics and goals of the study, the procedures, voluntary participation, possibility of quitting at any moment, and confidentiality of the data. Written informed consent was obtained from the subjects before beginning the study. For those players who were minors, the written consent of their parents was obtained. Procedures

All the tests were carried out on 3 consecutive weeks and each one was done at least 48 hours after the most recent game. Between the initial evaluation (E1) and the final evaluation (E2) there were 16 weeks of training, which consisted of the first half of the regular season. Before the tests were completed, the subjects executed a standardized warm-up directed by the primary researcher along with the coach. During the execution of these tests, the players were verbally encouraged to give their maximal effort. The tests executed by both teams for the measurement of performance are explained in detail below. Measuring Force

Force was measured in standardized conditions in a laboratory through the following tests: a CMJ, a CMJ with external load on the Smith machine, and a progressive FS with external load on the Smith machine. Countermovement Jump. The height of the jump on a contact platform (Ergo Jump Bosco System, S. Rufina di Cittaducale, RI, Italy) was measured. Each athlete completed 5 jumps. Two minutes of rest for complete recovery was given between jumps. The best and the worst jumps were eliminated from the data, and the average of the other 3 jumps was recorded. The coefficient of variation for test–retest reliability (CV) and the intraclass correlation coefficient (ICC) for this test were 5.8% and 0.95 (0.92–0.97), respectively. After the 5 jumps, the players executed the CMJ test with external load. Countermovement Jump with External Load on the Smith Machine. The height of the jump on a contact platform (Ergo Jump, Bosco System) was measured after 2 jumps. Four minutes

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50% 234 235

1234

FS (m!s21) (S 3 R) 1.2 8 3 4 1 6 3 6 1 3 3 6 0.9 4 3 4 0.9 2 3 4 0.9 2 3 4 0.8 2 3 4 0.8 3 3 4 0.8 4 3 4 HS (%W1m!s21) 100% 100% 110% 110% 120% 120% (S 3 R) 234 334 134 234 234 234 CMJL (%W 20 cm) 50% 50% 60% 60% 60% 70% 70% 70% (S 3 R) 434 234 334 134 334 334 534 434 CMJ 434 434 Sled towing 3 3 3 3 Step phase 235 335 435 635 635 435 435 435 435 triple jump DL 5 2 3 3

*FS = full squat; HS = half squat; CMJL = CMJ with load; m!s21 = load lifted in the FS test at 1 m!s21; %W1m!s21 = percent of the load lifted in the FS test at 1 m!s21; %W 20 cm = % of the load with which the player jumps approximately 20 cm. S 3 R = series 3 repetitions; DL = displacements with loads; CMJ = countermovement jump.

3

1 7 3 4 1 5 3 4 0.9 5 3 4 100% 90% 334 334 50% 50% 40% 734 534 534 634 435 435 3 3 6 635 635 6

2 2 2 1 1 Control test 2 2 1 1 1 2 1 2 Sessions per week Exercises

2

11 10 9 8 7 6 5 4 3 2 1

The players ran 3 30-m races on the artificial grass field, separated by 5 minutes for recovery. The starting position was standardized, with the lead-off foot behind the starting line. The photoelectric cell barriers were placed at the start, and at 10, 20, and 30 m. The players ran under the premise of running the 30 m in the least possible time. The quickest time of the 3 attempts in the following splits was recorded: 0–10 m (T10), 0–20 m (T20), 0–30 m (T30), 10–20 m (T10-20), 10–30 m (T10–30), and 20–30 m (T20–30). Wind speed was less than 1.5 m!s21, and wind conditions were monitored constantly by an Oregon Scientific WMR-918 (Oregon Scientific, Tigard, OR, USA) meteorological station. The CV for test–retest

Week number

Measurement of Acceleration Capacity

TABLE 1. Complementary training for team A each week volume and intensity of the session and exercises.*

Progressive Test of Full Squats with External Loads on the Smith Machine. The average speed in the concentric phase of the FS for each of the loads used was measured (CV 2.9–4%; ICC 0.92–0.94). This measurement was done with the Smith machine starting with a resistance of 20 kg (FS20). These data were obtained in real time through a Globus Real Power (Italy) digital rotary position transductor that was connected to the Smith machine bar through a steel cable. The transductor was connected to a portable computer on which force data were recorded, with a sample rate of 1,000 Hz and an incorporated timer with a precision of 0.2 microseconds. From the data, about the position of the cable and according to the time taken to complete the movement, the speed of movement was calculated. From this calculation and the displaced load in the multipower bar, the power that was generated was calculated. The number of repetitions executed by each athlete with each load was determined according to the speed of the first repetition. With the loads in which the subject moved the bar an average speed of $1 m!s21, 3 repetitions were done. When the subject moved the bar an average speed of ,1 m!s21, 2 repetitions were done. The best datum for speed of the repetitions done with external loads was the datum that was kept in mind for the later analysis. The increase in the load was done in 10-kg increments. Four minutes of recovery was taken between each series of repetitions. The test ended for each subject when the average speed of movement was less than 0.7 m!s21. This speed was chosen as the reference because in a pilot study, it was observed that the maximum average power was attained at higher speeds.

12

13

14

15

of recovery was given between jumps, and each of the established loads was set with the Smith machine. The test began with a load of 20 kg (CMJ20), and the weight was increased in 10-kg increments. The test ended when the subject jumped a height of less than 20 cm. This height was used because jumps lower than that progressively decrease the reliability of the jump (43) and it decreases the risk of injury. The CVs for test–retest reliability for CMJ20 and CMJ30 were 4 and 4.3%, respectively, and the ICCs were 0.97 (CMJ20) and 0.93 (CMJ30).

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TABLE 2. Week of training for team A. Monday

Tuesday

Strength Field training training + take-offs/sled field training towing physical conditioning and physical conditioning and technical and technical and tactical work tactical work

Wednesday Rest

Thursday

Friday

Field training Strength strategy and training + shots field training take-offs/Sled towing progressions and 2 3 20’ 11 vs. 11

reliability for these variables were 1.2–2.6%. The ICCs were 0.92–0.99. Progressive Maximal Aerobic Speed Test

This is a test of maximal effort with progressive intensity that is done on a track with visual markers every 25 m. It is a test with a progression of 1 km!h21 every 2 minutes after the protocol of the University of Montreal Track Test (23), with the exception that the speed increments were continuous. The athletes followed a speed that was determined by audio cues, and the test ended when the athlete did not arrive at the designated marker. The initial speed of the test was 8 km!h21, and this speed increased continuously from the start of the test until the finish. This test estimates the MAS as an indicator of the aerobic power of the players. Maximal aerobic speed is defined as the minimum speed in which the oxygen consumption is maximal in a progressive test. Maximal aerobic speed was the speed that corresponded to the last stage completed by the subject according to the established protocol (23). Training

The players from team A carried out 4 weekly training sessions on the field in addition to a weekly match, throughout the period between the initial evaluation and the final evaluation. Of the 4 training sessions, 2 were focused on the development of the physical conditioning of the players. The work during these sessions was focused on the improvement of the aerobic performance of the soccer players. Therefore, the players

Saturday Sunday Match

Rest

executed interval high-intensity runs, physical–technical circuits, and game-like activities with small groups and large spaces, with the intent that the intensity during the 4- to 6minute series was maximal. This training was complemented by 1 or 2 specific-strength training sessions in the weight room with a duration of 30–45 minutes before the field training. Strength training was developed using essential exercises such as jumps with and without external loads, half squats, and FSs (Table 1). The loads used by each player were assigned according to the speed of movement of the Smith machine bar in the jump with load and the FS obtained in the initial test and the intermediate test for monitoring speed. The progression was done with the objective of having the players always work with a load that they were able to lift in a FS at approximately 1 m!s21. In our laboratory, we have observed that the speed of 1 m!s21 corresponds with approximately 55% of 1 repetition maximum (1RM) and 0.8 m!s21 to 70% of 1RM for the FS exercise. In the 10th week, the load moved in 1 m!s21 in the FS and the load with which each subject was able to jump approximately 20 cm were recalculated for the following weeks’ sessions. Strength training was completed on the field by executing displacements with loads (5 kg) with changes in direction in series of 6–8 seconds, series of 6–8 executions of the step phase of the triple jump, and take-offs of 15–20 m with resisted sled towing (10 kg). A week of training in the style of team A is demonstrated in Table 2. Players from team B executed 4 weekly training sessions on the field in addition to a weekly match during the first 8 weeks of

TABLE 3. Week of training for team B. Monday

Tuesday

Wednesday Thursday

Field training Scrimmage Field training physical conditioning recovery continuous jumps/take-offs running, small-sided matches, rest

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Rest

Friday Field training strategy, small-sided matches, games

Saturday Sunday Rest

Match

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TABLE 4. Number of training sessions and their duration for teams A and B. Team A

Team B

Number

Duration (h)

Number

Duration (h)

64 32 23 118

1.75 1.75 0.75 185.25

40 16 0 56

1.75 2

Technical/tactical Physical conditioning Strength training Total

102

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competition. During the following 8 weeks, they executed 3 weekly training sessions in addition to a weekly match. During both periods, of the 3 or 4 weekly training sessions, 1 session had the primary objective of developing the physical condition of the players. During that session, the players executed continuous running series of low to moderate intensity, intervallic training of moderate to high intensity, and game-like activities in small

TABLE 5. Initial and final test results for the variables used for the evaluation of physical conditioning in under-19 soccer players.*† Team A

CMJ (cm) CMJ20 (cm) FS20 (m!s21) FS30 (m!s21) FS40 (m!s21) FS50 (m!s21) FS60 (m!s21) FS70 (m!s21) T10 (s) T20 (s) T30 (s) T10–20 (s) T10–30 (s) T20–30 (s) MAS (km!h21)

Team B

E1

E2

SE

E1

E2

35.37 6 5.1 (n = 13) 22.78 6 3.6§ (n = 13) 1.37 6 0.15 (n = 12) 1.27 6 0.13 (n = 12) 1.16 6 0.11 (n = 12) 1.06 6 0.12§ (n = 11) 0.88 6 0.17 (n = 12) 0.78 6 0.14 (n = 8) 1.82 6 0.06§ (n = 13) 3.08 6 0.11 (n = 13) 4.25 6 0.15§ (n = 13) 1.24 6 0.05 (n = 13) 2.4 6 0.09§ (n = 13) 1.15 6 0.05§ (n = 13) 16.39 6 0.28 (n = 15)

37.12 6 4.5 (n = 13) 24.33 6 3.4‡ (n = 13) 1.45 6 0.12‡‡ (n = 12) 1.36 6 0.12‡‡‡§ (n = 12) 1.22 6 0.12‡‡‡ (n = 12) 1.1 6 0.12 (n = 11) 0.93 6 0.14 (n = 12) 0.82 6 0.16 (n = 8) 1.85 6 0.1 (n = 13) 3.15 6 0.13‡‡ (n = 13) 4.35 6 0.19‡‡ (n = 13) 1.28 6 0.04‡‡‡ (n = 13) 2.48 6 0.09‡‡‡ (n = 13) 1.18 6 0.05‡ (n = 13) 16.91 6 0.9‡‡§§ (n = 15)

0.34

34.2 6 5.1 (n = 12) 18.93 6 2.9 (n = 12) 1.33 6 0.1 (n = 11) 1.256 0.1 (n = 11) 1.07 6 0.15 (n = 11) 0.89 6 0.19 (n = 11) 0.78 6 0.14 (n = 9) 0.74 6 0.11 (n = 5) 1.88 6 0.05 (n = 10) 3.16 6 0.1 (n = 10) 4.4 6 0.15 (n = 10) 1.27 6 0.06 (n = 10) 2.5 6 0.12 (n = 10) 1.22 6 0.07 (n = 10) 15.72 6 1.3 (n = 13)

35.44 6 5.2 (n = 12) 22.9 6 4‡‡ (n = 12) 1.39 6 0.07 (n = 11) 1.29 6 0.08 (n = 11) 1.15 6 0.1 (n = 11) 1.01 6 0.12‡ (n = 11) 0.87 6 0.17‡ (n = 9) 0.87 6 0.1 (n = 5) 1.85 6 0.06§ (n = 10) 3.14 6 0.09§§ (n = 10) 4.36 6 0.17§§ (n = 10) 1.27 6 0.03§ (n = 10) 2.49 6 0.1§§§ (n = 10) 1.2 6 0.07‡§ (n = 10) 15.66 6 1.2 (n = 13)

0.44 0.59 0.72 0.52 0.33 0.32 0.27 0.36 0.58 0.58 0.88 0.89 0.6 0.78

SE 0.24 1.14 0.7 0.44 0.63 0.76 0.58 1.24 20.54 20.21 20.25 0 20.09 20.29 20.05

*Values represented as mean 6 SE. CMJ = countermovement jump; CMJ20 = countermovement jump with 20 kg; FS20 = full squat with 20 kg; FS30 = full squat with 30 kg; FS40 = full squat with 40 kg; FS50 = full squat with 50 kg; FS60 = full squat with 60 kg; FS70 = full squat with 70 kg; T10 = time 10 m; T20 = time 20 m; T30 = time 30 m; T10–20 = time 10–20 m; T10–30 = time 10–30 m; T20–30 = time 20–30 m; MAS = maximal aerobic speed; E1 = initial evaluation; E2 = final evaluation; SE = size effect. †Intragroup analysis (‡p # 0.05; ‡‡p # 0.01; ‡‡‡p # 0.001). Intergroup analysis (§p # 0.05; §§p # 0.01; §§§p # 0.001).

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Aerobic Power, Strength, and Acceleration spaces. A week of training in the style of team B is demonstrated in Table 3. The comparison between the number of sessions and total work time for the 2 teams in presented in Table 4.

14 points after 4 wins, 10 losses, and 2 ties. This team made 17 goals, and its opponents made 31. These numbers resulted in a 14th-place position, which is a position that descends to the second national division.

Statistical Analyses

DISCUSSION

Standard statistical methods were used to calculate the means and SDs. A covariance test was used to compare the teams in E1. A t-test for related samples was used to compare E1 and E2 measurements. The alpha-level was set at p # 0.05. The SPSS 15.0 statistics package was used for the analysis.

RESULTS The results of the initial (E1) and final (E2) performance measurements for both teams are presented in Table 5. Countermovement Jump and Countermovement Jump with Load

For these variables, each group improved in performance, but they were not statistically significant differences. On the other hand, for the CMJ20 variable, both teams significantly improved (team A, p # 0.05; team B p # 0.01). For the comparison between teams, team A had a statistically significant better score (p # 0.01) for the CMJ at E1 than team B. These differences were not found at E2. Progressive Full Squat Test with External Loads on the Smith Machine

The average speed of displacement during the concentric phase on the Smith machine improved for both teams with all of the tested loads. These improvements were significant for team A for FS20 (p # 0.01) and highly significant (p # 0.001) for FS30 and FS40. Team B had statistically significant improvements (p # 0.05) for FS50 and FS60. Team A had significantly better scores (p # 0.05) for FS50 at E1 and for FS30 at E2. Maximal Aerobic Speed

For this variable, team A improved significantly at E2 (p , 0.01), whereas team B worsened. The differences between the 2 teams at E2 were significant (p , 0.01). Acceleration Capacity

Team A worsened its performance in all splits, and this decrease in performance was statistically significant for tests T20, T30, T10–20, T10–30, and T20–30. Team B improved in splits T10, T20, T30, T10–30, and T20-30, and this was significant (p # 0.05) in T20–30. The significant differences (p # 0.05) found in T10, T30, T10–30, and T20–30 in favor of team A at E1 were not observed at E2. At E2 the differences are significant for team B for all the distances tested. Classifying Position

After the first half of the regular season, coinciding with E2, both teams had played 16 matches. Team A achieved a total of 28 points, after 9 wins, 6 losses, and a tie. It made 26 goals, and its opponents made 18. These numbers resulted in a sixth-place position in the classification. Team B achieved

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The present paper studies the changes in physical performance (strength, acceleration capacity, and aerobic power) because of different training orientations in 2 under-19 soccer teams. Regarding jump capacity, team A improved in the CMJ (5%) and CMJ20 (6.8%). Team B improved in the CMJ (3.2%) and significantly in the CMJ20 (20%). Team A’s improvements in both tests are similar to those found in under-19 soccer players after 11 weeks of training (5.1% for the CMJ and 7.5% for the CMJ20) (14). The players from that study performed 2 weekly strength sessions executed with light and moderate loads at high speeds of contraction, similar to team A. This training program of explosive strength could explain the improvement in the vertical jump. The training carried out by team B achieved smaller improvements in CMJ. The large increase obtained in the CMJ20 may be because the training that this team executed during the preseason did not achieve optimal force levels at E1. The lesser experience of this team in this type of jump for external loads may have also influenced the initial results. These aspects could also explain the fact that team B improved significantly more than team A did. As a result of these changes, the statistically significant difference found at E1 in favor of Team A for the CMJ20 does not appear at E2. In another study with professional players (36) that also trained twice weekly during the 7-week preseason, with 3–5 series of 6–4RM in half squats, the nonsignificant improvements in the CMJ were similar (4.9%). Within the same team, another group executed the same training in addition to plyometric exercises (double-arm single-leg forward jumps, single-arm alternate-leg forward bounces, and double-leg hurdle jumps) and obtained slight insignificant improvements in the CMJ (1.9%). With these data, it seems that the use of maximal efforts (XRM) for soccer players has no advantages for the improvement of jump capacity when compared with using light and moderate loads at high contraction speeds. With regard to the application of force measured through the bar movement speed in the FS, both teams improved with all loads. Although team A’s improvements of were greater with loads lifted at a speed higher than 1 m!s21, team B’s improvements were greater with loads lifted below 1 m!s21. The training executed by team B achieved greater improvements at lower speeds, though it was less effective when high contraction speeds were required. Team A’s improvements in strength application evaluated by the jump and the FS, when compared with team B, are lower than expected after the execution of complementary strength training. This may be because of the high load of endurance training by team A. The same tendency was found in a study done with

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Journal of Strength and Conditioning Research physically active university students (5). The subjects were divided up to work on strength training, endurance training, or a combination of the 2 for 12 weeks. The improvement of strength measured by the 1RM for the knee extension was significantly greater (p , 0.05) in the group that worked on strength training only. Between the subjects that worked on only endurance training and those that worked on both strength and endurance training, there were no differences in _ 2max. However, the group that the improvement of the Vo worked on both qualities improved less in strength but significantly increased the number of capillaries per muscle fiber and the activity of the succinate dehydrogenase enzyme. That study showed that the combination of the 2 types of training can reduce the improvements in strength and favor the capilarization of skeletal muscle, increasing its oxidative capacity. Other studies have also found inhibitions in the improvement of strength when this training was executed simultaneously with endurance training (16,22). In the study done by Gorostiaga et al. (14), where subjects executed a complementary strength training program, as team A from the present study did, the improvements produced by this training program decreased as the load lifted increased, and therefore, the contraction speed of the musculature involved was lower. If the speeds at the intermediate control test and at E2 are taken into account, it can be concluded that the players from team A never trained at speeds of 0.8 m!s21. This is based on the fact that the proposed loads of 0.8 and 0.9 m!s21 after E1 were lifted at 0.9 and 1 m!s21 in the intermediate control test, respectively, and this speed was maintained at E2. Therefore, it can be concluded that that the subjects never trained at speeds of 0.8 and 0.9 m!s21, which could explain the lesser improvement in application of strength when faced with the loads moved at these speeds. In our laboratory (unpublished data), we have verified that for the FS, the load lifted at 0.8 m!s21 corresponds to 70%RM. Consequently, we can confirm that in the present study, improvements were achieved in strength application while training with loads that were less than 70%RM and without the use of XRM. This avoids the risks that the calculation of the 1RM and the use of the XRM involve. We consider this new possibility, based on a strength training program that is determined by the displacement speed of the Smith machine bar as a consequence of strength application, very useful for programing strength training for all athletes and especially for soccer players. From the data obtained in this study, it has been verified that the use of external loads that are determined by speed displacement, without needing to calculate a 1RM nor use X maximal repetitions (XRM) as proposed in other studies (18,19,36, 44,45), is an adequate work methodology for the improvement of the strength application in under-19 soccer players. Regarding acceleration capacity, team A decreased after the 4 months of training and competition in all the splits evaluated. All the decreases in performance were significant except for T10 (1.6% for T10, 2.3% for T20, and T30, 3.2% for T10–20, 3.3% for

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T10–30, and 2.6% for T20–30). Team B improved minimally in T10 (1.6%), T20 (1%), T30 (1%), T10–30 (1%), and T20–30 (1%), but the improvement was only significant in T20–30. The results of teams A and B are similar to those found for under-19 soccer players in 10 m (1.87 seconds) (7,15), in 20 m (3.1 seconds) (26), and in 30 m (4.38 seconds) (7). The values for professional soccer players are slightly lower in 10 m (1.8 seconds) (9,44), in 20 m (3 seconds) (44), and in 30 m (4 seconds) (44) and 4.2 seconds (9). However, for the comparison of the results, it should be taken into account that the surfaces over which the speed was measured were different. Moreover, some values can be influenced by the accumulated fatigue after the execution of other tests. When comparing the 2 teams’ acceleration capacity at E1, team A obtained better results in all splits, and the difference with team B was statistically significant in T10, T30, T10–30, and T20–30. At E2, team A worsened in acceleration capacity, whereas team B improved minimally, but this was only significant for team B in T20–30. Despite these changes, when applying the covariance analysis at E2, team B improved more in all the splits. The large quantity of aerobic work accumulated by team A’s players in their training could explain the lack of improvement in these variables. Only a small part of team B’s weekly training session was dedicated to training this quality. This volume of work does not appear to have enough stimulus to significantly improve this aspect among the soccer players that were evaluated. Team A’s training program for acceleration capacity included take-offs with sled towing, displacements with loads, and the step phase of the triple jump. The work with resisted sled towing has produced improvements in the capacity for acceleration in previous studies (24). This exercise, similar to the displacements with loads and the executions of the step phase of the triple jump, is executed while unilaterally involving the musculature of the lower body to bring about horizontal displacement. This similarity with the execution of a sprint favors the transfer that is sought in these exercises and with the strength training done by team A for the improvement of acceleration capacity (46). Despite what was expected, the stimulus brought about by both these exercises and the strength training was insufficient. Team A’s improvement in strength application of the lower body was not accompanied by an increase in the performance in acceleration capacity, which did occur in an intervention with professional soccer players (36). In that study after 7 weeks of preseason, the improvement in the lower-body strength of the experimental group brought about significant improvements in the capacity for acceleration that the control group did not experience. However, with under-19 players, after 11 weeks of strength training during the competitive period of the season, the capacity for acceleration did not change (14). It is important to consider the moment of intervention. The study by Ronnestad et al. (36)was done during the VOLUME 24 | NUMBER 10 | OCTOBER 2010 |

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Aerobic Power, Strength, and Acceleration preseason, with a large improvement in all the variables that were evaluated after the players’ seasonal break. The present study, like the one by Gorostiaga et al. (14), was done during the competitive period. As stated previously, the high aerobic work volume could have been responsible for inhibiting part of the potential adaptations in strength application in team A. In the same way, the improvement in acceleration capacity attempted through training with load displacements, resisted sled towing, and the step phase of the triple jump could also be compromised. Therefore, team B’s training program, which not only dedicated less time to training acceleration capacity, but also had an aerobic training component with less volume and less intensity, was effective. Having less interaction with the endurance training possibly allowed for this improvement. The time spent by each team on developing their physical conditioning (the high aerobic work volume) was reflected in changes in aerobic power. Team A’s aerobic power significantly improved when this was estimated through the MAS, increasing from 16.39 to 16.91 km!h21. After the 16 weeks of training and competition, team A’s improvement in this variable was significantly higher than that of team B. Team B’s aerobic speed worsened, although not significantly so, after the 4 months of training. Their MAS decreased from 15.72 to 15.66 km!h21. Team A’s MAS is similar to that obtained in professional players (17.1 km!h21) with the application of the same measurement protocol (10), whereas team B’s is lower. The number of sessions that team A executed for physical conditioning and the exercises executed in these sessions within the 16 weeks of training and competition could result in the improvement of the performance for this variable. Team A’s use of running intervals and game-like activities at 4–6’ of high intensity in the conditioning sessions has been employed in previous studies with soccer players as an effective method for improving maximal oxygen consumption (8,15,25). Executing the first test after at least 6 weeks of training, within the first week of the competitive period, may be the cause of the lower improvements (3.2%) when compared with the improvements in another study done with an under-19 population (10.8%). In that study (15), the initial evaluation of the aerobic power (V_ O2max) was done at the beginning of the preseason. Team B executed fewer physical conditioning training sessions. Team B’s training, with the use of moderate intensity running and game-like activities and with the volume dominating over the intensity of the effort, and with the low number of training sessions, may explain the slight decrease in the MAS. Previous studies have related the capacity for physical performance with final performance in competition (final ranking) (1,45). Along these lines, team A would be better equipped than team B at E1 to face the competitive demands. This assertion can be deduced from these players’ superior physical performance in all the tests. In 2 Norwegian first division teams, the V_ O2max and maximal strength in half

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squats presented significant differences in favor of the better classified (45). Arnason et al. (1) found similar results when comparing the best classified teams’ players of the first 2 Irish divisions. In this study, significant differences were observed in the V_ O2max. However, these authors only found a significant correlation between the teams’ average heights in the CMJ and in the squat jump and the final position in the classification (p = 0.009 and p = 0.012, respectively). Although the final classification could depend on technical, tactical, and strategical factors, in the present study, team A possessed greater strength application capacity, acceleration capacity, and MAS, and it achieved a better classification than team B. Within the 4 months of training and competition between E1 and E2, both teams played 16 official league matches (the first half of the regular season). Although team A achieved 28 points, team B achieved 14 of the 48 possible points, resulting in a position that would descend to the second national division. At E2, team A again had better performance values in the tests that were evaluated. After the following 16 competitive weeks, team A maintained its position finishing in sixth place and achieving 27 of the possible 48 points. Team B descended. Future studies with a longer duration and with a higher number of participating teams would help in the interpretation of the adaptations that different types of training provide in the physical performance of soccer players throughout a season. They would also help in the interpretation of the possible relationship between physical performance and the competitive results of different soccer teams with similar competitive demands.

PRACTICAL APPLICATIONS The following were noted: (a) Complementary strength training that is determined according to the speed of execution of the gesture can improve the levels of strength application in soccer players. This method also avoids the risks that determining and using the 1RM or XRM can involve. (b) The use of the speed of bar movement, as a consequence of the applied strength in the FS, can be used as a variable to monitor and individualize the strength load for training. (c) Because of the possible interference of the volume of aerobic training with the application of strength and acceleration capacity, it is necessary to control the amount of work done by the players. (d) The level of physical performance for the teams influences their final classification for under-19 soccer players.

ACKNOWLEDGMENTS The authors would like to express their gratitude to the Soccer Federation of the Region of Murcia, especially its President, Mr. Jose´ Miguel Monje; its General Secretary, Mr. Jose´ Fernańdez Soria; its Athletic Director, Mr. Jesu´s Rosagro; and its Human Resources Director, Mr. Juan Jose´ Villanueva; for the support received with the project" Effect of training and competition on body composition, strength,

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Journal of Strength and Conditioning Research speed, endurance, and various physical performance indicators in under-19 soccer players in the First Division." The present study has been done thanks to the Soccer Federation of the Region of Murcia and the Catholic University San Antonio.

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