Different loading schemes in power training during the pre-season promote similar performance...

Journal of Strength and Conditioning Research Publish Ahead of PrintDOI: 10.1519/JSC.0b013e3182772da6

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Different loading schemes in power training during the pre-season promote similar

performance improvements in Brazilian elite soccer players

Irineu Loturco1,2,3, Carlos Ugrinowitsch1, Valmor Tricoli1, Bruno Pivetti3, Hamilton Roschel1( )

1 - School of Physical Education and Sport, University of São Paulo, São Paulo, SP, Brazil

2 - Pablo de Olavide University, Faculty of Sport, Seville, Spain

3 - Pão de Açúcar Nucleus of High Performance in Sport, São Paulo, SP, Brazil

Hamilton Roschel, Ph.D. ()

School of Physical Education and Sport, University of São Paulo

Av. Prof. Mello Moraes, 65. Butantã, 05508-030 - São Paulo, SP, Brazil.

Tel: +55 11 3091-3120

Fax: +55 11 3813-5091

e-mail: [email protected]

Running Title: Power training in elite soccer players

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JSCR-08-1955 – Revision 4

ABSTRACT

The present study investigated the effects of two different power-training loading

schemes in Brazilian elite soccer players. Thirty two players participated in the study.

Maximum dynamic strength (1RM) was evaluated before (B), at mid-point (i.e. after three

weeks) (T1), and after six weeks (T2) of a pre-season strength/power training. Muscle power,

jumping, and sprinting performance were evaluated at B and T2. Players were randomly

allocated into one of the two training groups: velocity-based (VEL: n=16; 19.18 ± 0.72 years;

173 ± 6 cm; 72.7 ± 5.8 kg) or intensity-based (INT: n=16; 19.11 ± 0.7 years; 172 ± 4.5 cm;

71.8 ± 4.6 kg). After the individual determination of the optimal power load, both groups

completed a 3-week traditional strength-training period. Afterwards, the VEL group

performed three weeks of power-oriented training with increasing velocity and decreasing

intensity (from 60 to 30% 1RM) throughout the training period whereas the INT group

increased the training intensity (from 30 to 60% 1RM) and thus decreased movement velocity

throughout the power-oriented training period. Both groups utilized loads within ± 15%

(ranging from 30 to 60% 1RM) of the measured optimal power load (i.e. 45.2 ± 3.0% 1RM).

Similar 1RM gains were observed in both groups at T1 (VEL: 9.2%; INT: 11.0%) and T2

(VEL: 19.8%; INT: 22.1%). The two groups also presented significant improvements

(within-group comparisons) in all of the variables. However, no between-group differences

were detected. Mean power in the back squat (VEL: 18.5%; INT: 20.4%) and mean

propulsive power in the jump squat (VEL: 29.1%; INT: 31.0%) were similarly improved at

T2. The 10-m sprint (VEL: -4.3%; INT: -1.6%), the jump squat (VEL: 7.1%; INT: 4.5%), and

the counter movement jump (VEL: 6.7%; INT: 6.9%) were also improved in both groups at

T2. Curiously, the 30-m sprint time (VEL: -0.8%; INT: -0.1%) did not significantly improve

for both groups. In summary, our data suggest that male professional soccer players can

achieve improvements in strength and power-related abilities as a result of 6 weeks of power-

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oriented training during the pre-season. Furthermore, similar performance improvements are

observed when training intensity manipulation occurs around only a small range within the

optimal power training load.

Keywords: sprint performance; jump height; mean propulsive power; optimal load; power

training

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INTRODUCTION

It is well established that muscular strength and power play a significant role in soccer

performance (3-4, 10, 17, 20, 27). A top-class player performs 150-250 high-intensity and

explosive activities during a soccer game (1). Kicking, jumping, sprinting, accelerating, and

changing direction are important tasks within a soccer-match. Thus, strength and power have

become decisive for professional soccer players (24). In this regard, the use of resistance

exercises at the optimal power training load (i.e. the load that elicits the maximal power

production in a specific movement, 30-60% 1RM) (9) constitutes an important training tool,

as it has been shown to successfully increase power ability in sport-specific movements in

both physically active and well-trained individuals (6-8, 19, 22).

Despite of these previous findings, considerable controversy exists regarding the

manipulation of the training intensity around the optimal load throughout a training period.

In this concern, the manipulation of both the intensity and velocity of the training loads have

been long thought to significantly affect the force-velocity relationship and thus power

development and performance (13, 19). The classical concept of training periodization

assumes that overall training volume should decrease with a concomitant increase in training

intensity over time (23). However, one may speculate that, in spite of the previous suggestion

that strength and power gains can be achieved with maximal will lifting (32), this paradigm

may actually defy the specificity of power-training adaptations, as increasing training

intensities would impair movement velocity and thus compromise power ability in sport-

specific tasks. In fact, it has been proposed that the transfer of training to performance may be

maximized if training loads allows for similar movement velocities when compared to those

of the intended sport (9, 11, 18-19).

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Therefore, it is plausible to assume that a velocity-based loading scheme using loads

within the optimal power-training load range [i.e. increasing velocity and thus decreasing the

relative intensity (% 1RM) over time] throughout a given training period may be

advantageous over a traditionally employed intensity-based training program, in which the

relative intensity increases over time, thus hampering velocity production.

The present study investigated the effects of two different power-training loading

schemes in Brazilian elite soccer players. We hypothesized that a loading scheme that

favored increased movement velocity over time would greatly increase power in low external

load tasks such as sprinting and jumping when compared with a traditional loading scheme

(i.e. increased intensity over time).

METHODS

Experimental Approach to the Problem

In order to test if a velocity-based approach in power training is superior to the

classical one (i.e intensity-based), the present study evaluated the effects of two different

power-training loading schemes on the power development of Brazilian elite soccer players

during their pre-season training period. Subjects’ maximum dynamic strength (1RM) was

evaluated before (B), at mid-point (i.e. after three weeks) (T1), and after six weeks of a pre-

season strength/power training (T2). Muscle power, jumping, and sprinting performance were

evaluated at B and T2. Before the beginning of the training protocol, the individual’s optimal

power load (i.e. the load that elicits the maximal power production) (9) in the jump squat

exercise was also determined. The optimal power load in the jump squat was used as a

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reference load during the power training period. Afterwards, subjects were randomly

allocated into one of the two training groups: velocity-based (VEL) or intensity-based (INT).

As it has been suggested that training status (e.g. strength level) may play a role in power

ability (5, 26, 31), all of the subjects completed a 3-week strength-oriented training period

using the back squat exercise (50-80% 1RM) in order to minimize such effect. In this regard,

it is important to note that although the players had previous experience in strength training, a

30-day off-season period preceded the study. Then, a 3-week power-oriented training period

took place. Power training consisted of jump squats with either increasing velocity (VEL) or

increasing intensity (INT) every two training sessions. During the power-oriented training

period, both groups utilized loads within ± 15% (ranging from 30 to 60% 1RM) of the

measured optimal power load for the jump squat exercise (i.e. 45.2 ± 3.0% 1RM). The

experimental protocol took place during the players’ pre-season (6-week period) for the State

Championship. Figure 1 depicts the sequence of events over the experimental period.

INSERT FIGURE 1 HERE

Subjects

Thirty two professional soccer players regularly competing in both the State and

National Championships were randomly allocated into one of the two groups: a velocity-

based group (VEL: n = 16; 19.18 ± 0.72 years; 173 ± 6 cm; 72.7 ± 5.8 kg), and an intensity-

based group (INT: n = 16; 19.11 ± 0.7 years; 172 ± 4.5 cm; 71.8 ± 4.6 kg). Players have been

engaged in regular soccer training for at least 10 years and have been competing in a

professional level for at least 18 months. Subjects were informed of the experimental risks

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and signed an informed consent form prior to the investigation. The investigation was

approved by an Institutional Review Board for use of human subjects.

Maximum dynamic strength test (Squat 1RM)

The back squat 1RM test [within-group coefficient of variability (CV) < 5%] was

performed using a Smith machine (Cybex International, Inc. MA, USA). Subjects ran for five

minutes on a treadmill (Movement Technology®, Brudden, São Paulo, Brazil) at 9 km·h-1,

followed by five minutes of lower limb light stretching exercises. Afterwards, they performed

two squat warm-up sets. In the first set, subjects performed eight repetitions with 50% of the

estimated 1RM and in the second set they performed three repetitions with 70% of the

estimated 1RM (1RM estimation was based on their previous year pre-season 1RM testing

values). A 3-min resting interval was allowed between sets. Three minutes after the warm up,

participants had up to five attempts to obtain the 1RM load (e.g. maximum weight that could

be lifted once using proper technique), with a 3-min interval between attempts (2). Strong

verbal encouragement was given throughout the test.

Mean power (MP) in the Squat Exercise

All of the subjects were instructed to perform two sets of three repetitions of the

parallel back squat exercise with maximal speed at 60% of the 1RM load in the Smith

machine. A linear transducer (T-force, Dynamic Measurement System, Ergotech Consulting

S.L., Murcia, Spain) was attached to the Smith machine bar. Bar position data was sampled at

a frequency of 1000 Hz and recorded into a computer. Finite differentiation technique was

used to estimate the bar velocity and acceleration. The mean power (MP) on each repetition

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of the back squat exercise was obtained by multiplying the average force by the average

speed, over the entire concentric phase (MP) (within-group CV < 10%). The duration and

amplitude of the concentric phase were determined by taking the lowest and the highest

position instants of the Smith machine’s bar on each repetition. The duration of the

propulsive phase of the concentric phase of each repetition was defined as the time interval in

which the acceleration of the Smith machine’s bar was positive (25).

Mean power (MP) and mean propulsive power (MPP) in the Jump Squat Exercise

This test was performed following the same basic procedures described for the

previous test. Subjects were instructed to start from a static squat position (i.e. ~90° of knee

flexion) and jump as high as possible without losing contact with the bar. For the optimal

power load determination, subjects were tested in a progressive overload fashion (starting

with 0% 1RM in 10% 1RM increments) until the maximum power was achieved. A 3-min

rest was given between each lift. The trial with the greatest power output was accepted for

further analysis. For the pre- and post-test evaluation, jump squat tests were conducted using

45% 1RM. The mean propulsive power (MPP) on each repetition of the jump squat exercise

was obtained by multiplying the average force by the average speed, over the entire

concentric phase (MP) and positive acceleration region of the concentric phase (MPP)

(within-group CV < 10%). The duration and amplitude of the concentric phase were

determined by taking the lowest and the highest position instants of the Smith machine’s bar

on each repetition. The duration of the propulsive phase of the concentric phase of each

repetition was defined as the time interval in which the acceleration of the Smith machine’s

bar was positive (25).

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Jump Squat and Counter Movement Jump (CMJ)

The jump squat was performed from an initial static position at 90o knee angle.

Subjects were instructed to maintain their hands on their waist and freely determine the

amplitude of CMJ in order to avoid changes in jumping coordination (31). Additionally, an

experienced researcher conducted all of the tests and visually checked for counter-movement

occurrence during the SJ in order to ensure reproducibility. They performed five jumps with a

15-s interval between attempts (within-group CV < 10%). Jumps were executed on a contact

platform (Winlaborat, Buenos Aires, Argentine). The best and the worst jumps were

discarded and the average of the remaining jumps was used for data analysis purpose.

10-m and 30-m Sprint Test

Three pairs of photocells were used to mark the starting point (i.e. 0-m), 10-m, and

30-m distances (within-group CV < 10%). Subjects accelerated as much as possible for 5 m

before crossing the starting point. They performed two attempts and the best one was

considered for further analysis.

Training Protocols

The strength-oriented training period (first three weeks) was composed of regular

back squat exercises. The strength-oriented training period followed standard load

progression, with loads ranging from 50 to 80% 1RM (16). The power-oriented training

period (following three weeks) was comprised of jump squat exercises. All of the exercise

sets were interspersed by a 2-min interval. Total training load was equated across the training

groups. During the power-training period, the VEL group increased the exercise velocity and

decreased the exercise intensity within ± 15% of the measured optimal power load (i.e. 45.2 ±

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3.0% 1RM), going from 60% 1RM during the first week to 45% 1RM during the second

week and ending the training period with a lighter load (i.e. 30% 1RM) and greater

movement velocity. The INT group increased exercise intensity within the established range

of the measured optimal power load (i.e. from 30 to 45 to 60% 1RM, during weeks 1, 2, and

3, respectively), thus decreasing exercise velocity. Players from both groups were instructed

to move the load as fast as possible and to jump as high as possible during the entire power-

oriented training period. All of the training sessions were supervised by an experienced

strength and conditioning training coach. The entire pre-season training period (6 weeks)

involved not only the strength/power training (twice a week), but also, training for general

development of soccer-specific technical-tactical skills (four times a week). Importantly, the

soccer-specific technical-tactical training was the same for both groups. Figure 2 depicts the

details of the strength/power training protocol for each group over the 6-week pre-season

training period.


Statistical Analysis

Data normality was assessed through visual inspection and the Shapiro-Wilk test. All

of the variables presented a normal distribution. Mixed models assuming group (VEL and

INT) and time (B and T2) as fixed factors and subjects as a random factor were used for the

MP, MPP, SJ, CMJ, 10-m and 30-m sprint speed analyses. An additional level for time was

considered when analyzing the 1RM data (B, T1, and T2). In case of significant F-values, a

Tukey adjustment was used for multiple comparison purposes. Significance level was set at

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p≤0.05. An initial analysis revealed no between-group differences for any of the variables at

B.

RESULTS

The strength-oriented training period was effective in increasing maximum dynamic

strength. At T1, both groups displayed comparable gains in 1RM (VEL: 9.2%; INT: 11.0%).

Similar strength gains were also observed between VEL and INT when compared at T2

(VEL: 19.8%; INT: 22.1%) (Figure 3).


Both groups similarly improved MP in the back squat exercise at 60% 1RM (VEL:

18.5%; INT: 20.4%) and MPP in the jump squat exercise at 45% 1RM at the end of the

training period (VEL: 29.1%; INT: 31.0%) (Figure 4 A and B). Accordingly, the 10-m

sprinting was similarly improved after T2 (VEL: -4.3%; INT: -1.6%) (Figure 4 C). The

jumping performance increments for both the SJ and the CMJ were also comparable across

groups (VEL: 7.1%; INT: 4.5% and VEL: 6.7%; INT: 6.9%, respectively) (Figure 4 E and F).

Curiously, the only variable that did not present a significant improvement for neither group

was the 30-m sprint time (VEL: -0.8%; INT: -0.1%) (Figure 4 D).


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DISCUSSION

We hypothesized that a loading scheme favoring increased movement velocity over

time would greatly increase sprinting and jumping performance when compared with a

traditional loading scheme (i.e. increased intensity and decreased velocity over time) within a

6-week training period. The findings reported herein do not support our hypothesis as distinct

power-oriented training schemes produced similar performance improvements. Furthermore,

the results of the present study suggest that different variations of the loading schemes around

the optimal load for power training may constitute similarly effective stimuli to improve

performance and muscle power production ability.

The training schemes used in the present study (i.e. VEL and INT) targeted at

developing the power abilities in the different components of the power equation. For

instance, the heavier loads (60% 1RM) utilized within the power-oriented training period

would favor increases towards the high-intensity end of the force x velocity curve whereas

the lighter intensities (30% 1RM) would provide improvements towards the high-velocity

end of the curve. As a distinct temporal organization of the lighter and heavier loads was

provided between VEL and INT, we expected that it would differently affect the low external

load tests (i.e. sprinting and jumping).

It has been previously demonstrated that distinct power-training loads (i.e. between 30

and 100% of the maximal isometric force) promote similar increases in maximal power and

velocity in the elbow flexion (28-29). However, both studies utilized single-joint movements.

Conversely, the study by McBride et al. (19) demonstrated that ballistic training using

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different intensities (i.e. 30 and 80% 1RM) produced load-specific adaptations. Only the low-

intensity group displayed a significant increase in peak power in the low-intensity (30%

1RM) jump squat whereas the high-intensity group improved the 50 and 80% 1RM jump

squat peak power.

One may argue that the loads employed in the latter study were considerably different

than the ones used in the present study. That may actually have been the case. However, as

several studies have suggested that the use of the optimal load for power training (i.e. the load

that elicits the maximal power production in a specific movement) (9) may constitute an

effective stimulus for power development, we opted for varying loads within a spectrum

around the optimal load and keeping a more feasible approach to realistic training scenarios.

Nonetheless, it is tempting to speculate that if a broader range of loads were used, a different

outcome could have been found. Supporting this concept, others have also found that when

testing loads that were not dramatically different (i.e. ~50 vs. 80% 1RM), comparable results

were found between groups in sport-specific tasks across an intermediate- to high-velocity

spectrum (12).

Furthermore, it is possible to speculate that the lack of differences between the

experimental groups in the post-training tests may be related to the rather short training

period adopted (6-week pre-season training period). Although we agree with such argument,

it is imperative to highlight the fact that the pre-season in professional soccer in Brazil

consistently ranges from 4-6 weeks. Additionally, other studies have shown performance

improvements in similar time-frame pre-season periods (15, 30, 33). Alternatively, we could

have designed a 6- instead of a 3-week power-oriented training. However, as athletes were

previously in an off-season period, and given the previous suggestions that training status

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(e.g. strength level) may play a role in power ability (5, 26, 31), we opted for a 3-week basic

strength-training period. Moreover, it has been advocated that combining the development of

both the components of the power equation (i.e. strength and velocity) may reflect in better

power development across a training period (14, 21, 28), further corroborating our strategy.

Finally, unfortunately, it is unfeasible to conceive that coaches and professional players will

be available for a year-round experimental study, which could interfere with their training

program. Instead, the cooperation with the Brazilian professional soccer team in this study,

constitutes an unique opportunity to gather knowledge regarding strength training effects on

soccer players’ performance during their actual pre-season training

Nonetheless, caution should be exercised when considering the practical application

of our findings. Even though the subjects of the present study were elite Brazilian soccer

players it is possible that these athletes are sensitive to a more dramatically different

distribution of the training loads across the training period.

In summary, our data suggest that trained individuals have similar performance

improvements when training load manipulation occurs just around the optimal load for power

training.

PRACTICAL APPLICATIONS

Soccer competitive seasons are becoming longer and, consequently, less time is

devoted for pre-season preparation. The current study indicates that male professional soccer

players can achieve improvements in strength and power-related abilities as a result of 6

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weeks of power-oriented training during the pre-season. There were no differences in

performance between treatment groups, indicating that both forms of training load

manipulation (i.e. velocity- or intensity-oriented) were equally effective. Thus, our results

highlight the possibility of using both strategies to improve the power-related components of

soccer. In addition, we suggest that coaches involved in power-training for team sports such

as soccer should be concerned about the selection of the most appropriate training load range

rather than with loading-schemes variations. According to our results, we suggest that using

loads within a small range around the individual’s peak power output (e.g. from 30-60% of

the 1RM, assuming a measured optimal power training load of 45% 1RM) leads to

improvements in power-related performance during the pre-season training period in elite

soccer players.

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Acknowledgments

C.U. (470207/2008-6) and VT (304814/2010-5) are supported by Conselho Nacional

de Desenvolvimento Científico e Tecnológico (CNPq).

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Figure legends

Figure 1. Timeline of the study design over the 6-week period. MP: Mean Power (W); MPP:

Mean Propulsive Power (W); V-10: 10-m sprint time; V-30: 30-m sprint time; JS: jump squat

height; CMJ: counter-movement-jump height.

Figure 2. Training protocol for groups VEL and INT throughout the 6-week training period.

INT: intensity-based group; VEL: velocity-based group.

Figure 3. Squat 1RM (kg) for both the velocity-based (VEL) and the intensity-based (INT)

groups at baseline (B), after three weeks of strength-oriented training (T1) and after three

weeks of power-oriented training (T2). * indicates p<0.05 when compared with B (intra-

group comparison); ** indicates p<0.05 when compared with T1 (intra-group comparison).

Figure 4. Mean Power [MP in Watts (W)] in the squat exercise using 60% 1RM (Panel A);

Mean propulsive power [MPP; in Watts (W)] in the jump squat using 45% 1RM (Panel B);

10-m and 30-m sprint time (sec) (Panels C and D, respectively); jump squat height (cm)

(Panel E); counter-movement jump height (cm) (Panel F). * indicates p<0.05 when compared

with B (intra-group comparison).

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