Authors:  Rıdvan Çolak1, Eda Ağaşcıoğlu2

1 Department of Physical Education and Sports, Ardahan University, Ardahan, Turkey.
2Department of Sports Training, Galata University, İstanbul, Turkey.

Corresponding Author:
Rıdvan Çolak, Ph. D., Assistant Professor
E-mail: [email protected]
GSM: +905556229421, Fax: +904782117514
Orcid ID: https://orcid.org/0000-0002 -7998-5847

Rıdvan Çolak, Ph. D., is an Assistant Professor of Physical Education and Sports at Ardahan University in Ardahan, Turkey. His research interests focus on free radicals and protein oxidation markers associated with exercise, exercise at altitude, physical activity and performance related measurements.

Eda Ağaşcıoğlu, Ph. D., is an Assistant Professor of Training at Galata University in İstanbul, Turkey. Her research interests focus on free radicals and protein oxidation markers associated with exercise, exercise and ageing, hypoxia, physical activity and performance related measurements.

An evaluation of professional regional soccer goalkeepers using three different choice reaction times and vertical jumps

ABSTRACT

Soccer goalkeepers’ (GKs) role in a team is important, but they are either disregarded or considered like fielders in current literature. This study aims to evaluate 1) soccer GKs’ reaction times with tree different decision making visual reaction time tests (shapes, directions and number), 2) relationship between reaction times and vertical jumps (Countermovement Jump (CMJ) and Squad Jump (SJ)). Turkish professional male soccer players were classified into four groups: GKs, defenders (DFs), midfielders (MFs) and attackers (ATs) (n = 10 for each). Reaction times and vertical jumps tests were done using Sport Expert TM-MPS-501. One-way ANOVA and Pearson Correlation of SPSS V.22 were used for data analysis. GKs were taller and heavier than fielders. GKs were fast in number reaction time (NumRT) and shape reaction time (ShaRT) than fielders, but they had no difference in direction reaction time (DirRT). GKs had higher scores in both vertical jumps than MFs and DFs, but not ATs. In general, the high negative correlations were observed between vertical jumps, and ShaRT and NumRT in GKs. The results illustrate that professional GKs are as talented as ATs; however, considering their height and body mass, they may be the best in motor abilities.

Key Words: soccer players, shape reaction time, number reaction time, direction reaction time, countermovement jump, squad jump

INTRODUCTION

Soccer is one of the most popular sports in the World (26) and played in almost all countries. Professional soccer playing demands special talents. There are many of studies that examine physiological parameters of soccer players. Most of these studies are related to fielders (11, 39, 41, 42) not soccer goalkeepers (GKs). However, the role of soccer GKs in success of a team is not negligible. Only a few studies have investigated soccer GKs. These studies are mainly focused on training approaches (14, 18, 29), and general performance characteristics comparing with those of fielders’ (2). In these, strength, power, agility type of physical characteristics of GKs are studied which are similar to field players. There might be other unique physical characteristics of GKs which would differ from fielders i.e., fast reaction and accuracy.

Reaction time is a measure of time elapsing between the onset of a stimulus and the initiation of the action (12, 23). It has been related to motor performance, which often depend on the rapid reactions required to perform successfully basic tasks such as defending an unpredictable goal from an opponent’s attack. Reaction times can be measured in three different ways; simple, choice or discrimination reaction time (23). Simple reaction time is only one signal and only one response. It does not require a decision (27). Choice reaction time necessitates more than one signal and each signal has a specified response, which requires decision-making or integration (23, 33). Discrimination reaction time requires more than one signal but only one response (23).

GKs always have to adjust their behavior to altering conditions (15). It looks that reaction time for GKs is not a simple reaction. It requires a very quick decision since GKs have to defend a ball coming from different directions, different players with different numbers. Therefore, we thought that choice visual reaction time and different type of stimuli are more important for GKs.

GKs should perform short lasted, explosive actions with high level of technique (22). In other words, they have to react quickly in response to a stimulus with powerful performance. GKs’ role requires quick whole-body movements and directional changes (40), which is termed as agility (34). GKs need to be agile in order to defend a goal with changing speed and direction with taller and heavier body mass (8).  In order to react and move quickly with big bodies, GKs have to have strong and powerful leg muscles. In soccer, performance of fielders and GKs is influenced in great extent by lower limp power (1, 5). Throughout the world, countermovement jump (CMJ) and squad jump (SJ) are considered as valid and outstanding ways of determining leg muscles’ power CMJ gives information about the reactive strength of the leg muscles (38), while SJ provides information about lower limp power performance (3, 38).

Both vertical jumps have been used as a measure of lower limp power in soccer (10, 20, 42). The research has illustrated that there is a relation between vertical jump performance and both 10m and 30m sprint time in well-trained elite soccer players (42). A SJ and a CMJ of soccer GKs were similar to those of the fielders, though they have big body masses (1). Sporis et. al., (35) reported that soccer GKs have higher body masses then the fielders. In brief, GKs have to jump better in order to leap vertically to catch or deflect the ball quickly against their relatively big body masses. In other words, shorter reaction time for GKs mandates stronger and powerful leg muscles. In the current study, we thought that power of leg muscles support reaction time of soccer GKs. Therefore, determining professional GKs’ jumping performance with relation to reaction time could give an idea about training strategy.

GKs react against several types of visual stimuli and they have to move against a ball in changing condition that require decision-making reaction not simple reaction. Moreover, soccer GKs have to react quickly with their big body mass to catch a ball, which requires powerful lower limps. Therefore in this study we aimed to determine a) whether or not there is a difference among three different types of visual stimuli i.e., ShaRT, NumRT and DirRT in decision making (choice) reaction time measurement, b) whether or not there is relationship between choice visual reaction times and vertical jumps (CMJ and SJ).

METHODS

Participants

In the current study, forty Turkish professional male soccer players were classified into four groups: GKs, defenders (DFs), midfielders (MFs) and attackers (ATs) (n = 10 for each). All participants were professionals and played in the regional league teams. Demographics and anthropometric information of soccer players were illustrated in Table 1. A stable stadiometer (Seca 217, Germany) was used to measure weight and height of participants. The body fat percentages (BF %) were determined by Tanita Electronic Scale (Model TBF 300, Germany) and overnight fasting-state nude weight of participants was measured to ± 0.01 kg. According to the description of Morrow et al., (25) body mass index (BMI) was calculated. All participants had 10-12 years of professional experience, in which they exercised 3-5 hours a day and 5-6 days per week. Inclusion criteria required players to be professional soccer players in Turkish first league, free from current injury at the time of testing, and currently participating in full soccer training. They were also asked not to take any caffeine during the three hours before the `12` measurements and to keep their regular diet and sleep regimens prior to experiment date. All participants were informed about the tests and participants gave their consent before data collection.

 Measurements of Visual Reaction Times

The visual reaction times were measured by a portable reaction time device (Sport Expert MPS-501, Tümer Engineering, CO., Turkey). The device had three parts, which are 1) central unit having LCD display screen, 2) stimulus generator and 3) junction box. Junction box had sensors pads (piezo type hand switches). Stimulus generator had visual apparatus. 

The participants were required to press either of the touch pads with the same type of the stimuli. The central unit measures the duration between the participants seeing the stimuli and pressing touch pad. Each visual reaction time tests (shapes, directions, and numbers) with different stimuli were taken with three-choice visual signals. Triangle, circle, or square shapes of stimuli were used for shape type of visual reaction time test. Right, left, and forward arrows were used for direction type of reaction time measurement. Finally, 1, 2 or 3 numbers were used for number type of reaction time measurement. Each stimulus is appeared inside an 8X8 matrices multi-color LED screen. During the measurements, soccer players were asked to stay 10 cm away from sensor pads and to react to each visual stimulus by touching the same stimuli type relevant pad as fast as they could. Soccer players were asked to use their dominant hand. The device was arranged to give a stimuli every 3 seconds over a 20 second-time period for each visual reaction time test. First, visual reaction time measurement was demonstrated by the researcher and then each player had a trial. After that, the actual measurements were taken. They repeated the test twice and the best one was selected as their result for each reaction time measurements. Before each measurement, a ‘ready’ command was given by the researcher.

Countermovement Jump and Squad Jump Measurements

All the soccer players performed both vertical jump protocols with a different apparatus of Sport Expert TM, MPS-501 device (Tümer Electronic LDT., Turkey). This device was a conductor carpet (dimensions L-175 x W-70 cm) connected to an electronic timing system. The timer switched on automatically when a subject jumped and switched off at the time when a foot made contact with the plate again. The height of the both jumps were recorded as centimeters.

The players’ soles were on the platform; their feet were parallel and a shoulder width apart. They were asked to keep good balance of upright position and their trunk remained as vertical as possible while their hands kept on the hips throughout the test. For CMJ, the soccer players stood straight (0 degree “180-degree” knees angles) for 2 s and then performed a jump beginning with a counter movement down to a knee angle of 90 degrees, because, the optimal range of movement for CMJ testing is about 90 degrees knee flexion. For SJ, initially the participants held about 3 s with 90 degrees knees angles position. Then they were asked to jump up as much as possible with maximum power for each jumping protocol. The device began to measure at the instant the soccer player took-off from the mat and stopped at the instant of landing contact on the mat. After three trial jumps, the best one was recorded for both jumping protocols. Then calculations of the jump height were automatically made by the device, which was based on description of Bosco et. al. (9).

Data Analyses

Descriptive statistics were given as mean and standard deviation (SD). All data were normally distributed and the variances of the data were homogeneous. A one-way analysis of variance (ANOVA) was run for the data analysis of each reaction times and vertical jumps with a Tukey post-hoc correction. A Pearson correlation matrix was used for determination of the relationship between reaction times and vertical jumps. All data were processed using SPSS V.22 (IBM, Chicago, IL, USA). When not specified, p < 0.05 was considered significant.

RESULTS

Demographics and Anthropometric Characteristics of Goalkeepers and Fielders

Demographics and anthropometric characteristics for all groups of soccer players are given in Table 1. Results indicated goalkeepers were taller than ATs (p=0.001), DFs (p = 0.014) and MFs (p = 0.003). They were also heavier than ATs (p=0.004), and MFs (p = 0.025). However, there were no statistical difference observed in age, BF % and BMI among the soccer players.

Table 1. Demographics and anthropometric characteristics of GKs and fielders, with means and standard deviations (SD).

Variable GKs (n=10)
Mean ± SD		 DFs (n=10)
Mean ± SD		 MFs (n=10)
Mean ± SD		 ATs (n=10)
Mean ± SD
Age (years) 20.90 ± 2.02 21.30 ± 1.56 20.80 ± 1.75 21.40 ± 1.78
Height (cm) 1.85 ± 0.04 1.77 ± 0.07* 1.76 ± 0.03* 1.75 ± 0.05**
Weight (kg) 78.18 ± 7.62 70.39 ± 8.51 69.22 ± 3.27* 67.19 ± 6.17*
BF % 13.08 ± 5.22 10.53 ± 3.25 11.30 ± 3.36 10.86 ± 2.80
BMI (kg/m2) 22.92 ± 2.06 22.36 ± 1.76 22.42 ± 1.44 21.99 ± 1.58

GKs= goalkeepers, DFs= defenders, MFs= midfielders, ATs= attackers; SD= standard deviations.  *p <0.05 or **p<0.001 indicates significantly greater values of GKs compared to fielders.

Choice Reaction Times

GKs generally had the shortest reaction time scores in number, direction and shape reaction time measurements among the soccer players (Figure 1, 2, 3). GKs had statistically better scores in NumRT measurement than ATs (p= 0.014), DFs (p = 0.005) and MFs (p = 0.002). Similarly, they had statistically lower scores in DirRT than ATs (p= 0.019) and MFs (p = 0.033), while they illustrated no difference from DFs. In ShaRT they had significantly lower score than DFs (p = 0.011) and MFs (p = 0.032).

Figure 1. NumRT-Çolak
Figure 1. Differences in NumRT scores between GKs and fielders. NumRT= number reaction time, GKs= goalkeepers, DFs= defenders, MFs= midfielders, ATs= attackers; *p <0.05.
Figure 2. DirRT-Çolak
Figure 2. Differences in DirRT scores between GKs and fielders. DirRT=direction reaction time, GKs= goalkeepers, DFs= defenders, MFs= midfielders, ATs= attackers; *p <0.05.
Figure 3. ShaRT-Çolak
Figure 3. Differences in ShaRT scores between GKs and fielders. ShaRT= shape reaction time, GKs= goalkeepers, DFs= defenders, MFs= midfielders, ATs= attackers; *p <0.05.

Countermovement Jump and Squad Jump

Significant differences were apparent in CMJ and SJ among GKs, ATs, DFs and MFs (Table 2). CMJ performance of GKs were statistically higher than DFs (p = 0.001) and MFs (p = 0.015) but there was no difference between GKs and ATs. Moreover, GKs performed higher SJ than DFs (p = 0.011) and MFs (p = 0.047), while there was no difference between ATs and GKs.

Table 2. CMJ and SJ measurements of GKs and fielders are demonstrated with means and SD.

Variable GKs (n=10)
Mean ± SD		 DFs (n=10)
Mean ± SD		 MFs (n=10)
Mean ± SD		 ATs (n=10)
Mean ± SD
CMJ (cm) 41.9 ± 2.12 36.8 ± 3.01** 38.03 ± 3.33* 40.1 ± 2.23
SJ (cm) 39.9 ± 1.66 35.3 ± 3.23* 36.1 ± 3.92* 38.2 ± 3.23

GKs= goalkeepers, DFs= defenders, MFs= midfielders, ATs= attackers; CMJ= countermovement jump, SJ= squad jump, SD= standard deviations; *p <0.05, **p<0.001.

Correlations of Visual Reaction Times and Vertical Jumps

There was statistically significant high correlation between ShaRT and CMJ in GKs (p = 0. 006), MFs (p = 0.021) and ATs (p = 0.035). There was also statistically high correlation between ShaRT and SJ in GKs (p = 0. 026), MFs (p = 0.022) and ATs (p = 0.042). A correlation was only observed in GKs between NumRT and CMJ, and NumRT and SJ (p=0.021, p=0.019 respectively). Albeit, there were no correlations between any of the reaction time measurements and jumping performances in DFs. There were no correlations observed between jumping performances and DirRT in any groups of other players (Table 3).

Table 3. Correlations between jumping performances and visual reaction times measurements.

Groups (n=10 for each) Jumps ShaRT DirRT NumRT
GKs CMJ -.791* -.403 -.713*
SJ -.695* -.225 -.720*
DFs CMJ -.485 -.099 -.011
SJ -.395 -.136 -.218
MFs CMJ -.710* -.390 -.103
SJ -.708* -.388 -.104
ATs CMJ -.666* -.436 -.089
SJ -.651* -.315 -.001

GKs= goalkeepers, DFs= defenders, MFs= midfielders, ATs= attackers ShaRT = shape reaction time, DirRT = direction reaction time, NumRT = number reaction time; CMJ = counter measure jump, SJ = squad jump; *p < 0.05.

DISCUSSION

Being worldwide popular sport, professional soccer playing requires special talents for not only field players but also GKs. There are restricted number of studies related to soccer GKs (14, 18, 26, 29). The role of soccer GKs in a team success is critique. The present study investigated professional soccer GKs’ reactions against different types of visual stimuli, relations of choice reaction times with vertical jumps and difference of GKs in these parameters from fielders.

The study outcomes show that professional soccer GKs were taller than ATs, MDs, DFs, and they are heavier than ATs, MDs. Their BF percentage and BMI were similar to fielders (Table 1). These findings are in line with the literature. Croatian premier league GKs were also heavier, taller than fielders, but Croatian premier league GKs had higher BF percentage (24). Davis et al (13) reported that English premier and second division league’s GKs were heavier than fielders were, as well. These results imply that professional GKs are generally taller, heavier than fielders with higher or similar BF percentage are.

Since reaction time is an important aspect of professional athletes (4, 17) and visual signal perception has priority for soccer GKs, in the present study, three different visual choice reaction time tests were chosen. The choice reaction time lasts longer than the simple reaction time (30). The increase in the number of stimulus-response alternatives increases the choice reaction time, as well (16, 19). Soccer GKs have to react fast and accurate in response to unpredictable stimulus i.e., a ball coming from changing directions (22). Besides, they should execute these motor skills requiring constant adaptation. In the current study, professional GKs scored the shortest time in NumRT than all fielders (Figure 1). In DirRT, there were no difference between GKs and DFs, while GKs were faster than MFs and ATs (Figure 2). In ShaRT, GKs were better than MFs and DFs, but they got similar scores with ATs (Figure 3). GKs are generally better at all three reaction time tests. These results emphasize that besides their inherited motor skills, the GKs should receive a specific training. GKs should pay attention to the numbers on ATs’ uniform of an opponent team in order to follow coming attacks during a game. Moreover, GKs should have a well-developed spatial perception in relation to changing position of the ball and opponent team’s players. This means GKs should follow a ball as the ATs do and they should be as fast as DFs in changing direction during the game. In fact, GKs with their big body masses have to be quick at whole-body movements and directional changes (8, 40) in pursuit of the spatial orientation of the game.

Professional GKs are trained for long periods of time for every possible probability to catch a ball, which improves their decision making and performance. Savelsbergh et al. (31) studied skill-based differences in anticipation and visual search behavior during the penalty kick in professional and novice soccer GKs. They pointed that expert GKs were generally more accurate in anticipating the direction of the penalty kicks. Savelsbergh et al. (32) further investigated successful or unsuccessful expert soccer GKs on visual search behavior during simulated penalty kick situations. They reported that the successful experts were more accurate in predicting the height and direction of the penalty kick, waited longer before initiating a response. Linford et al. (21) demonstrated that neuromuscular training leads to lessen the reaction time. In their study, six weeks neuromuscular training program was applied on five men and eight women of the peroneus longus muscle of the electromechanical delay and reaction time. Moreover, Zouhal et al., (39) illustrated that 6 weeks of neuromuscular training with two sessions per week, significantly improved agility performance in professional soccer players. Aforementioned four studies would be an ample evidence about training effects on reaction time and support the findings of the shortest reaction time scores of professional GKs in the present study.

In the literature, the studies illustrated that left hand would be better than right hand (6, 7), or dominant hands would be generally better than non-dominant hands in reaction (28). In the current study, all the soccer players were asked to select their dominant hand. Therefore, hand selection in the study would not be a case for GKs success in three different reaction times. Silverman (36) stated that the shortest way neural impulse travels the fastest reaction time takes place. The neural impulses involved in the production of a motor response have less distance to travel in women than in men. Because women are on average shorter than men. Since being the tallest among the soccer players, GKs have natural disadvantage in reaction time, though they had better scores in three choice visual reaction time measurements. All these mean that GKs with their taller and heavier bodies should have higher motor abilities to become successful.

GKs have to perform fast, accurate and explosive actions on right time with high level of technique, though being taller and heavier than fielders.  This inquired us to think about the power of leg muscles. The present study results demonstrated that professional GKs are as good as ATs and they are better than DFs and MFs at both SJ and CMJ (Table 2). Similarly, Sporis et al. (35) tested SJ performance of GKs from premier league of Croatia and they demonstrated that GKs jumped higher than fielders did. Albait, Arnason et al. (1) tested that SJ and CMJ performances of the Icelandic elite and first divisions’ soccer players and they found that SJ and CMJ performances of GKs were similar to those of the fielders in the study. However, in the same study a leg extensor power test results illustrated that GKs had higher power values than the fielders. Arnason et al. (1) concluded that higher leg extensor power did not result in higher jumping scores due to the higher body mass of GKs. Considering absolute vertical jumps scores, the studies illustrate that either GKs have similar scores to the fielders or they are better than the fielders are. However, if vertical jumps scores were taken into account relative to a body mass, GKs would appear to be the best among the other soccer players.

In this study, we wondered whether there is a correlation between vertical jumps and three different visual reaction times. To the best of our knowledge there is no study looking for a relation between vertical jump and reaction time in soccer GKs in the literature. Both SJ and CMJ jumps showed correlation to ShaRT in GKs, MFs and ATs, but not in DFs. There were no relation between vertical jumps and DirRT in all soccer players. However, both SJ and CMJ correlates to NumRT only in GKs (Table 3). Şahin (37) demonstrated that vertical jump was highly correlated with acceleration and agility in young volleyball players. According to Coker (12) and Magill (23), when reaction time finishes, the movement time begins. In another words, stimuli lead to mental processing, mental processing leads to an action. This information supports the present study results that GKs’ success to defend a ball, contrary to the longer processing time due to their height, requires even higher power potential of leg muscles. 

CONCLUSION

The present study showed that professional GKs are better at three different choice visual reaction time tests and vertical jumps despite having the biggest body mass among soccer players. This underlines that being GKs necessitates high level of motor abilities in spite of being taller and heavier. This inherited talent of GKs is supported by power of leg muscles.

APPLICATION IN SPORT

The future soccer GKs should be selected among the ones who has the highest motor abilities requiring mental processing. They should also be genetically tall. Moreover, their training programs should be oriented to develop motor abilities, while developing leg muscles power.

ACKNOWLEDGMENTS

The authors would like to acknowledge regional league soccer goalkeeper Gökhan Eşençayı who volunteered to help this project and assisted in data collection. The authors also thank all the soccer players of the regional league soccer teams who participated voluntarily in this research, for their time and effort.

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