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Original Research

The Effect of a 4-Week Training Regimen on Body Fat and Aerobic Capacity of Professional Soccer Players During The Transition Period

Sotiropoulos, Aristomenis1; Travlos, Antonios K2; Gissis, Ioannis3; Souglis, Atnanasios G1; Grezios, Apostolos3

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Journal of Strength and Conditioning Research: September 2009 - Volume 23 - Issue 6 - p 1697-1703
doi: 10.1519/JSC.0b013e3181b3df69
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Abstract

Introduction

There are several studies in the scientific literature that report soccer is a dynamic, complex, and particularly demanding sport (21). Body fat percentage is an important parameter that can influence performance. Soccer players with a high body fat percentage, and therefore with extra body mass, have difficulty in meeting the demands of game and practice sessions, which require frequent changes between aerobic and anaerobic physiological systems (30). Scientific literature supports that the body fat percentage of top players can rise to 20% between seasons (25,27), and can reduce to approximately 10% during the playing season (17,27). It is also well known “that about 5% body fat is common in distance runners, and can be inferred that soccer players have traditionally carried more than an optimal amount of body fat, and that between seasons in particular it is important to limit the accumulation of body fat” (27, p. 763).

Aerobic capacity has been examined more than any other physiological variable as a representative parameter of good cardiovascular function in soccer (1,2,25). The nature of the game is such that it demands constant mobility on the part of the player. The variety of kinetic activities indicates that soccer players have to be in a state of constant motion and readiness in order to function efficiently in the environment of the game (20). This requires a sufficiently developed aerobic capacity, so that the player can be at a state of readiness for at least 90 minutes. The former component reflects the ability to produce aerobic energy at a high rate and is characterized by maximal oxygen intake (O2max). Aerobic capacity expresses the ability to sustain exercise for a prolonged period and is synonymous with endurance. The maximum oxygen intake for elite male players has been determined to range from 56 to 69 ml·kg−1·min−1 (26). These values are similar to those obtained in other team sports, but are considerably lower than those for elite athletes within endurance sports, where O2max in excess of 80 ml·kg−1·min−1 has been observed (26). Studies of soccer players show a variation in O2max that is influenced by stress at the time of testing and is also partly associated with the different positions of the players within the team (3,7,10-12,23,24,26,31).

The importance of aerobic capacity and body composition in soccer performance is of great interest for coaches and conditioning specialists. Soccer players that begin the competition season with a high level of fitness are able to improve their aerobic capacity and body composition from preseason to postseason (28). However, entering the season unprepared (e.g., high catabolic metabolic status), soccer athletes may experience reductions in performance and inefficient changes in body composition (15,28). Moreover, to meet the demands of high-intensity soccer games, it becomes apparent that professional soccer players have to at least maintain similar rates of body fat and aerobic capacity during the transition period as the ones developed during the playing season. Because goalkeepers carry more body fat (7) and have greater variation in aerobic capacity (24), they were not included in the study. Therefore, the purpose of this study is to evaluate the changes in body weight, body fat percentage, and aerobic capacity in professional soccer players, after the implementation of a specific 4-week training regimen during the transition period (end of May to the beginning of July).

Methods

Experimental Approach to the Problem

During the transition period, soccer players go on vacation and usually follow a “loose program” of low-intensity aerobic physical activities (e.g. jogging, beach volleyball, swimming). Most of the players return for the preseason preparation with extra weight and decreased aerobic endurance. To deteriorate this negative profile and for the purpose of evaluating the maintenance of aerobic capacity and body composition, soccer players had to follow a specific 4-week training regimen during the transition period (see Table 1). To examine the effect of the training regimen, we used professional soccer players of the Greek Premier Division that volunteered for the study at the end of the 2004-2005 National Football Association season. Soccer players were separated in experimental (specific program) and control groups (loose program) and measured for body composition (weight, percent body fat) and aerobic capacity at the beginning (pretest) and the end of the transition period (posttest).

Table 1
Table 1:
Transition period training program.*
Table 1
Table 1:
(continued) Transition period training program.*

Subjects

Fifty-eight professional soccer players of the Greek Premier Division served as volunteers for the study. All of them had at least 10 years of soccer experience (12.32 ± 2.40) and were playing in professional divisions for 5.20 ± 2.3 years. Twenty of the participants were randomly selected for the control group (age 24.4 ± 2.97 years, height 178.6 ± 4.1 cm) and the rest of them created the experimental group (age 23.2 ± 2.55 years, height 179.0 ± 4.5 cm). The Ethics Committee approved the study and all players consented to the study in writing before participation and were free to withdraw without repercussion.

Procedure

All soccer players were measured on aerobic capacity and body composition within a 6-day period (pretest measure). The training program started the next day and lasted 4 weeks. The training program included aerobic and strength conditioning activities (see Table 1, for a description of the transition period training program) and consisted of warm up, main training (strength and/or aerobic capacity maintenance), and cool down. The experimental group of soccer players followed the training program, while the control group did not participate in any specific training program. With the termination of the training program, the participants went through the same measures for the estimation of aerobic capacity and body composition (posttest measure).

Evaluation of Body Composition

Body weight was measured to the nearest 0.1 kg using a standard beam balance. Skinfold thickness was estimated using a Harpenden skinfold caliper (John Bull, British Indicators, Ltd., West Sussex, United Kingdom). Skinfold measures were taken in duplicate at seven sites (abdominal, triceps, chest/pectoral, midaxillary, subscapular, suprailiac, and thigh), according to the standards of the American College of Sports Medicine. Measures of chest, abdominal, and thigh were used for the calculation of body density (13). Siri's equation (29) was used to estimate percent body fat.

Evaluation of Aerobic Capacity

Maximum oxygen intake was measured on a treadmill (Powerjog). Initially, the athlete warmed up for 5 minutes on the treadmill at a speed of 7 km·h−1. This was followed by a regime of stretching exercises lasting 5 minutes, prior to the measurement procedure. A variation of the Bruce (4) protocol was followed. The procedure was as follows: The speed started at 10 km·h−1, and was increased by 1 km·h−1 every 2 minutes. The procedure was interrupted when the athlete indicated that he could no longer continue this effort, or when there was another indication that the tested athlete reached the maximum of his ability (oxygen uptake levels remained constant or reduced when the workload increased, value of respiratory quotient (R) exceeded 1.1, or cardiac frequency approached or exceeded maximum cardiac frequency [220-age]).

During the procedure the subject inhaled atmospheric air and exhaled through a tube into a gas analyzer (Sensor Medics Vmax 29, Yorba Linda, CA, USA). The analyzer was calibrated before each measurement using an air syringe of known quantity (3 L), and gases with specific concentrations of oxygen (16%) and carbon dioxide (4%). The criteria by which O2max findings were evaluated were those accepted by the American College of Sports Medicine.

Statistical Analyses

The experimental design used for analyzing weight (kg), percent body fat (%), and O2max values (ml·kg−1·min−1) was a 2 × 2 (Groups × Measures), with Groups as a between-subjects factor and Measures as a within-subjects factor. The assumptions associated with the aforementioned design were tested (14). Bonferroni's post-hoc analyses were used to further examine any statistical significance (8,14). The level of significance was set at p ≤ 0.05 for all analyses. The means and the standard deviations for body weight, percent body fat, and O2max values for experimental and the control groups as a function of pretest and posttest measures are presented in Tables 2-4.

Table 2
Table 2:
Pretest and posttest body weight (mean ± SD).
Table 3
Table 3:
Pretest and posttest body fat (mean ± SD).
Table 4
Table 4:
Pretest and posttest Table 1O2max values (mean ± SD).

Results

Body Weight

Analysis of variance of the body weight data indicated the main effects of groups did not reach statistical significance (F1,56 = 1.13, p > 0.05), while the main effect of measures and the groups by measures interaction reached statistical significance (F1,56 = 142.84, p < 0.0001 and F1,56 = 24.14, p < 0.0001, respectively). The significant main effect of measures was due to the increase of the overall weight at the posttest measure (78.45 ± 4.36) relative to the pretest measure (77.57 ± 4.21). Post-hoc analyses of the significant groups by measures interaction revealed the experimental group was not significantly different from the control group condition at the pretest (78.14 ± 4.77 and 76.48 ± 2.65, respectively) and posttest measures (78.74 ± 5.00 and 77.90 ± 2.82, respectively). However, the experimental and the control groups showed statistically significant increases in body weight from pretest to posttest measures (0.595 kg and 1.425 kg, respectively). Additional analysis indicated that the aforementioned differences were statistically significant (t56 = −4.91, p < 0.005).

Percent Body Fat

The results of the analysis of variance of the percent body fat data indicated a significant main effect of measures (F1,56 = 249.52, p < 0.0001) and significant groups by measures interaction (F1,56 = 70.81, p < 0.0001), while the main effect of groups did not reach statistical significance (F1,56 < 1, p > 0.05). The significant main effect of measures can be attributed to the overall increase of percent body fat during the posttest measure (8.31 ± 1.80) as compared with the pretest measure (7.87 ± 1.70). Post-hoc analyses of the significant interaction indicated that the experimental and control groups did not differentiate significantly at the pretest (7.92 ± 1.68 and 7.77 ± 1.79, respectively) and posttest measures (8.17 ± 1.81 and 8.59 ± 1.80, respectively). The experimental and control groups showed statistically significant increases in percent body fat (0.25 and 0.82, respectively) from pretest to posttest measures. Additional analysis of the aforementioned differences indicated that the control group (0.82 ± 0.29) gained significantly (t56 = −8.42, p < 0.005) more body fat than the experimental group (0.25 ± 0.22).

Maximal Oxygen Capacity (O2max)

The analysis of variance of the O2max values yielded a significant main effect for measures (F1,56 = 648.62, p < 0.0001) and a significant groups by measures interaction (F1,56 = 257.96, p < 0.0001). However, the main effect of groups did not reach statistical significance (F1,56 = 1.80, p > 0.05). The significant main effect for measures was due to the greater O2max values of the pretest (57.80 ± 2.56) as compared with the posttest measures (56.05 ± 2.83). Post-hoc analyses indicated that (a) the experimental (57.66 ± 2.56) and control (58.08 ± 2.60) groups were not significantly different at the pretest measures, (b) the experimental group (56.85 ± 2.52) was significantly better than the control group (54.52 ± 2.80) at the posttest measure, (c) the experimental group had a small but significant decrease (0.81 ml·kg−1·min−1) from pretest (57.66 ± 2.56) to posttest (56.85 ± 2.52), and (d) the control group showed a large and significant decrease (3.56 ml·kg−1·min−1) from pretest (58.08 ± 2.60) to posttest (54.52 ± 2.80) measures. Additional analysis on the pre-posttest differences between experimental (−0.81 ± 0.42) and control (−3.56 ± 0.89) groups indicated that the control group decreased significantly O2max values as compared with the experimental group (t56 = 16.06, p < 0.0001). The means for the O2max values for the significant interaction are plotted in Figure 1.

Figure 1
Figure 1:
Table 1O2 max values (ml·kg−1·min−1) of the experimental and control groups at the pretest and posttest measures.

Discussion

The training regimen was designed in order to maintain the values of the above-mentioned variables, rather than increasing them. Based on the present findings, it appears the absence of organized physical activity during the transition period adds extra kilograms of body fat to soccer players and decreases their aerobic capacity.

The results of this study demonstrated that the players in experimental and the control groups exhibited a significant increase in their body fat percentage within a 4-week time period. The soccer players that followed the training program achieved significantly lower body fat percentages as compared to the players that did not follow any organized training program. Moreover, the changes that have been observed on body weight can be attributed to the changes on body fat. Regarding the body fat percentage of professional soccer players, the present findings are in agreement with other studies (5-7,11,19,23,24,31). The body fat percentages were lower than those for men of the same age, who exhibit a mean body fat percentage of approximately 16%, but they were higher than the percentages for long-distance runners who exhibit mean body fat percentages between 4% and 7% (16).

Regarding the findings of O2max values, the present results indicated that after a four-week training program, the maximal oxygen capacity levels of the experimental group remained close to the initial measures (difference of −.81 ml/kg/min) as compared to the higher reduction in oxygen capacity by the control group (difference of −3.56 ml·kg−1·min−1). This finding is noteworthy as it indicates the players in the experimental group will begin the regular play season with higher O2max values as compared to the control group.

Comparing the O2max values of the experimental and control groups at the pretest and posttest measures with the values reported for Swedish (9) and German soccer players (22), it is reasonable to assume that the reported values of the tested Greek soccer players are at a moderate level. It may be the case that the players' coaches preferred to spend more time training with the ball rather than purely on physical conditioning (18).

It becomes apparent that soccer players have to be involved in organized physical activity during the off-season period in order to maintain physical conditioning components at reasonable levels that will permit them to return to their teams for their preseason preparation.

Practical Applications

The results of this study showed that the amount of body fat increased as aerobic capacity decreased after the application of a specified training program lasting 4 weeks during the transition period, when compared to the end of the regular play season during which the players were at peak playing activity. Of course, the players in the group that followed the training regimen demonstrated improved values, and therefore began their preseason period with better values than the players in the group that did not follow the regimen. As a result of this study, it is obvious that the application of a training program, as opposed to a suspension of training activities, is deemed necessary in order for the players to begin their preseason period at a satisfactory level of physical condition.

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Keywords:

soccer; body composition; maximal oxygen capacity (O2max); transition period

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