Effect of CR Supplementation on Athletic Performance
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To succeed in a given sport at any level of competition, athletes must possess specific physiologic, psychologic, and biomechanic traits critical to success in that sport, but they must also receive optimal physical, mental, and biomechanical training to maximise this genetic potential (Williams, Kreider & Branch, 1999). However many athletes believe that the combination of genetic traits and optimal training alone are not sufficient to achieve maximum performance, therefore the use of ergogenic aids has become common to improve sports performance beyond the effect of training (Sundgot-Borgen, Berglund & Torstveit, 2003). The use of ergogenic aids will allow athletes to gain that competitive advantage over opponents therefore leading to potential success. According to Williams, Kreider & Branch, (1999) ergogenic aids are substances or treatments that are theoretically designed to enhance physical power, mental strength or mechanical edge therefore potentially improving athletic performance.
Given the various demands of team sports such as Soccer, Rugby and Hockey, which require short intermittent bouts of high intensity exercise which are interspersed by low level exercise, it seems feasible the use of ergogenic aids in such sports may enhance and benefit performance to gain that competitive edge over opponents. One ergogenic aid which has become popular among amateur, professional and recreational athletes over recent years is Creatine Monohydrate (Cr). Creatine is a naturally occurring amino acid derivative which is found in skeletal muscle, but is also a normal dietary constituent with a daily requirement of approximately 2 to 3 grams depending on body size (Ostojic, 2001). The majority of creatine in muscles is stored in the form of phosphocreatine (PCr) which serves as an important contributor to energy metabolism during high intensity exercise (Williams, Kreider & Branch, 1999). PCr provides the high energy phosphate for adenine diphosphate (ADP) to restore adenine triphosphate (ATP) concentration rapidly via the Cr kinase (CK) reaction (Clarkson, 1996).
Hultman, Bergstrom and McLennan-Anderson, (1967) demonstrated that depletion of PCr stores within the muscles can lead to a decline in athletic performance during high intensity exercise, so theoretically increasing PCr stores through Cr supplementation would enhance the ability to maintain high intensity exercise over a prolonged period of time, leading to increases in sporting performance. Ahmun (2005) and Hultman, Soderlund, Timmons, Cederblad, & Greenhaff, (1996) demonstrated that the average Cr concentration in human muscle can be increased through Cr supplementation over a 7 day period from 20% pre Cr to 50% post Cr.
Since PCr is a substrate for the ATP-PCr energy system which is essential for high intensity exercise of 30 seconds or less it seems logical that the supplementation of Cr would be beneficial to exercise tasks of this duration. Therefore the majority of previous research has focused on bouts of anaerobic performance of <30 seconds.
To date the effect of Cr supplementation on athletic performance has been widely researched. This includes include positive effects of Cr supplementation over a prolonged period of over 4 weeks which is otherwise known as the maintenance phase (Knehans, Bemben, Bemben and Loftiss, 1998; Larson, Hunter, Trowbridge, Turk, Harbin and Torman, 1998). Also demonstrated have been positive effects of Cr supplementation on exercise performance using a shorter ingestion period known as the loading phase (Stout, Echerson, Noonan, Moore, and Cullen, 1999; Volek, Boetes, Bush, Putukian, Sebastianelli and Kraemer, 1997a). This includes improvements in performance variables such as strength, speed and delaying the onset of fatigue (Okudan and Gokbel, 2004; Volek, Kraemer, Bush, Boetes, Incledon, Clark and Lynch 1997b; Kocak & Karli , 2003)
Team sports consist of repeated bouts of intermittent high intensity exercise therefore consistently relying on the ATP-PCr energy system which if depleted can have a major factor on performance and the outcome of a game (Ostojic, 2004). One such sport which consists of repeated bouts of high intensity exercise is soccer. Soccer players are required to produce high power outputs and maintain or repeat them with only a few seconds of recovery, (Reilly and Williams, 2003). Such high intensity instances could be the deciding factor of a game, for example sprinting back to make a game saving tackle or sprinting past a defender to the ball to make a shot.
One high intensity exercise instance which occurs in a soccer match are bouts of sprinting, which are estimated to consist of 8.1% of a 90 minute match and occur approximately every 90 seconds lasting between two to four seconds in duration (Bangsbo, Norregard & Thorso, 1991). Given the fact that there is considerable support for Cr as an ergogenic aid it would be reasonable to suggest that a soccer players sprint performance would benefit from Cr supplementation. However there is minimal research which has looked into the effects of Cr on sprint performance and variables of soccer match play such as agility running, lateral stepping and running backwards( Cox, Mujika, Tumilty and Burke 2002; Ostojic, 2004; Mujika, Padilla, Ibanez, Izquierdo and Gorostiaga, 2000). The aforementioned studies have determined the effects of Cr on elite soccer players, female soccer players and youth soccer players (Ostojic, 2004; Mujika et al., 2000; Smart et al 1998; Cox et al., 2002). However there is no present research that looks into the effects of acute ( <7 days) Cr supplementation on sprint performance in amateur soccer players.
Another aspect to consider upon testing the effects of Cr on sprint performance on amateur soccer players is the protocol to be used. Although there have been many protocols which have been designed to measure and simulate soccer performance, plenty of these have failed to adequately simulate the different movement patterns (sprinting, walking, running backwards, lateral stepping) which are involved in a game of soccer (Drust, Reilly and Cable, 2000; Abt, Reaburn, Holmes and Gear, 2003; Thatcher and Batterham, 2004). It seems rational that when assessing components of soccer performance that the protocol that is utilised replicates the different activity patterns and demands of soccer match. If this is not taken into consideration it becomes difficult to determine whether Cr supplementation will have any benefit on soccer performance. Therefore the utilised protocol needs to concisely replicate movement patterns in soccer so that a valid assumption can be made to determine the erogeneity of acute Cr supplementation on sprint performance in amateur soccer players.
Thus the purpose of this study is to conduct an investigation that will determine the effect of acute Cr supplementation on sprint performance in Caucasian male amateur soccer players, using a soccer simulation protocol in an accurate, valid and reliable manner with two trials consisting over a 7 day period. Concluding whether or not acute Cr supplementation can be used as an ergogenic aid to improve a footballer's sprint performance, therefore recommending to athletes and coaches alike.
Creatine Monohydrate: Background
Creatine monohydrate is one of the most popular sporting supplements in the world today and is used by high school athletes, the elderly, professional and recreational athletes in the hope of improving physical performance (Bemben and Lamont, 2005). It is the most commonly available Cr supplement and the form primarily used in most research studies. Cr monohydrate comes in a number of forms including powder, tablets, gel, liquid, chewing gum and candy (Williams, Kreider and Branch, 1999, p.43). Greenhaff (1997) indicated powdered Cr, ingested with solution to have a quicker absorption rate at raising muscle Cr concentration than using Cr supplementation of a tablet form. Conversely Vuckovich and Michaelis (1999) reported no significant difference in absorption rate between the two different forms.
The supplementation dosages of Cr can be broken down into two different phases, otherwise known as the loading phase and maintenance phase. The loading phase that is commonly used in research consists of ingesting daily, 20-30g of Cr in four equal doses of 5-7g dissolved in around 250ml of fluid interspersed throughout the course of the day (preferably morning, noon, afternoon and evening) for a period of 5 to 7 days (Greenhaff, 1997; Kreider, 1997). Hultman et al (1996) utilised a less intense loading method of 3g/day for 28 days and proposed it to be just as effective as the aforementioned loading protocol.
However this method places a longer dependency on subjects to comply with the supplementation program, therefore placing more variables into the reliability of results. Following the loading phase, maintenance dosages are considerably lower. Most research investigating the effects of Cr using the maintenance phase, have utilised dosages of 3 to 15g over a 4 to 10 week period (Bemben et al., 2001; Kreider et al., 1998; Stone et al., 1999; Vandenberghe et al., 1997). It is recommended to consume Cr with warm water, as it facilitates the dissolving of the solution and also aid absorption (Harris et al., 1992). It should also be noted that the ingestion of caffeine during Cr supplementation eradicates its potential ergogenic effect (Vandenberghe et al., 1996; Van Leemputte, Vanstapel & Hespel, 1997). Vandenberghe et al (1996) demonstrated that a control group that ingested Cr combined with caffeine to have a lessened ergogenic potential compared to a group that ingested Cr without caffeine during repeated bouts of high intensity exercise.
There is no conclusive scientific evidence to suggest that Cr ingestion has any negative side effects utilising the proposed dosage methods ( Larson et al., 1998; Schroder, Terrados & Tramullas, 2005). There is further evidence to support this as Kreider et al (1999) found no negative side effects in athletes who had been ingesting Cr for up to 3 years. Poortmans and Francaux (1999) demonstrated similar findings for athletes for taking Cr for up to 5 years. Only undocumented anecdotal reports have reported any adverse negative side effects through Cr supplementation, this includes gastrointestinal distress, muscle cramping and dehydration (Associated press 1997, 1998).
Taking dehydration into consideration such anecdotal research can be scrutinised. Oopik, Timpmann and Medijainen, (1995) demonstrated that Cr supplementation increased body mass, while also reporting increases in total body water. Such findings signify that Cr supplementation may prevent dehydration rather than be a cause, due to the fact it can promote water retention.
Cr supplementation has been demonstrated to increase body mass by up to 2kg over an acute period of time (Balsom et al., 1995; Becque et al., 1997). This could be recognised as a negative side effect for athletes that compete in weight control sports, as Cr ingestion may impede their ability to make regulated weight in a forthcoming event. This gives a consensus that athletes in such activities need to be made aware that although Cr can promote gains in strength and power, it can increase body mass.
Physiology of Soccer
Soccer players are frequently required to produce high power outputs and maintain of repeat them with only a few seconds of recovery (Reilly and Thomas, 2003). This includes intermittent bouts of kicking, tackling, turning, sprinting, changing pace and maintaining balance and control of the ball whilst under pressure from an opponent (Wisloff, Helgerud & Hoff, 1998). To gain a scientific perspective of the different physiological demands of soccer performance, match and time motion analysis have been utilised (Bangsbo, 1994). This analysis has allowed researchers to determine the overall workload of players during a 90 minute match by calculating total distance covered, and the pattern of activities performed during a game (e.g. sprinting, cruising, walking etc).
Movement patterns of Soccer
It is estimated that the total distance covered during a 90 minute soccer match varies from 8.7km to 11.5km ( Bangsbo & Lindquist, 1992; Ekblom, 1986; Ohashi et al., (1988); Reilly and Thomas, 1976; 1988; Rampini et al., 2007; Wade, 1962). The large variance in distances covered are due in part to the differing styles of play, levels of competition and skill level of the teams that were utilised (Luxbacher, 1997).
Reilly (1994) documented the different activity patterns of elite outfield players from the English top division and other major national leagues in Europe and Japan using different methods of match analysis. Results found that a 90 minute match consists of 24% walking, 36% jogging, 20% cruising sub maximally (striding), 11% sprinting, 7% moving backwards and 2% moving in possession of the ball.
The categories of sprinting and cruising are defined as high intensity exercise. In terms of distances covered the ratio of low intensity exercise to high intensity exercise during a soccer match is 7 to 1 denoting that the outlay of energy for soccer is predominately aerobic ( Reilly and Thomas, 1976). However the importance for high intensity bouts during soccer match play should not be underestimated. The timing of such a bout could be the defining factor of a game whether in possession of the ball or without the ball. Although work-rate profiles are relatively consistent for players from game to game it is the high intensity exercise which is the most constant feature (Bangsbo, 1994).
The number of sprints reported in a soccer game varies greatly from 17 to 62 (Bangsbo et al., 1991; Mohr, Krustrup & Bangsbo, 2003). This variance is largely determined by the positional role of the player. Findings by Reilly (1996) demonstrated that midfielders and strikers completed more sprinting bouts than centre backs or full backs therefore relying more on the anaerobic energy system.
However if there is not a prolonged recovery period or an individual is not properly conditioned they will not subsequently recovery from high intensity bouts of exercise and fatigue will occur (Reilly, 1996). This is evident as Reilly (1996, p.72) documented that the majority of goals conceded during a soccer match occurred in the final ten minutes of play. A popular theory for this occurrence has been found to be mental fatigue or lapses in concentration from defenders (Reilly, 1996, p.72). However this can theory can be scrutinised as research found that the onset of fatigue in intermittent exercise such as soccer is caused by low muscle glycogen stores (Balsom et al., 1999).
Acute Cr supplementation and sprint performance in team sports
Athletes in team sports such as soccer, rugby, hockey and American football are required to repeatedly reproduce intermittent bouts of high intensity exercise with minimal recovery. Being able to consistently reproduce such bouts at maximal ability (e.g. sprinting, jumping, running backwards) could be the deciding factor in competition to gain that extra edge of an opponent. During high intensity exercise of an intermittent nature the main contributor of energy is PCr (Williams, Kreider & Branch, 1999, p29). Depletion of PCr stores during high intensity exercise has been found to be a factor which has lead to a decline in athletic performance (Hultman, Bergstrom and McLennan-Anderson, 1967). Through the supplementation of Cr, it hypothesised that PCr stores are replenished at a faster rate therefore improving an athlete's ability to recover and perform intermittent high intensity bouts of exercise, leading to improved athletic performance (Greenhaff et al, 1993).
There have been various studies that have tested this hypothesis by investigating the ergogenic effect of acute Cr supplementation on sprint performance of athletes in team sports (Ahmun et al., 2005; Cornish, Chilibeck & Burke, 2006; Izquierdo et al., 2001; Kocak & Karli, 2003; Romer et al., 2001; Vandebuerie et al., 1998). However the aforementioned studies have contrasting findings with a quantity of studies finding a significant improvement in sprint performance through Cr supplementation (Izquierdo et al., 2001; Romer et al., 2001; Vandebuerie et al., 1998). On the contrary other studies have found no significant improvements in sprint performance through acute Cr ingestion (Ahmun et al., 2005; Cornish, Chilibeck & Burke, 2006; Kocak & Karli, 2003).
Ahmun et al., (2005) investigated the ergogenic effect of Cr on sprint performance in male rugby players. For this study a Wingate test protocol was utilised prior and post Cr supplementation. Findings of this study were that there was no significant improvement in maximal cycle sprints through Cr ingestion. However in contrast Izquierdo et al., (2001) found that acute Cr supplementation improved sprint times in male hand ball players. For this study subjects were either assigned Cr or placebo over a 5 day period. The protocol that was utilised consisted of repeated sprint runs that were consistent with sprint distances achieved during handball match play. One issue that could have had a determining factor of the non significant results found by Ahmun et al (2005) is the protocol that was utilised.
A Wingate test was utilised to test the sprint performance in rugby players, however the relevance of a Wingate test to measure rugby performance is not sports specific there scrutinising the validity of the results. In contrast Izquierdo et al (2001) utilised a protocol which successfully replicated distances found in handball match play therefore maintaining validity. Ahmun et al (2005) also failed to incorporate a dietary analysis into the experimental design of the protocol, therefore whether or not Cr stores within the subjects utilised were full cannot be determined, which gives rationale for results showing no significant improvement. In contrast Izquierdo et al (2001) implemented a dietary examination of subjects that were utilised; this was initiated to determine whether any subjects had ingested Cr or any ergogenic aids prior to baseline testing. This assisted with maintaining validity during research. This can be supported by Romer et al (2001) and Vandebuerie et al (1998) who utilised a protocol containing a dietary analysis and concluded a significant improvement in sprint times within subjects.
Cr supplementation and Soccer performance
Given the intermittent physical demands of soccer, which requires players to produce high power outputs and maintain or repeat them with only a few seconds of recovery, (Reilly and Williams, 2003) it seems feasible that soccer players would benefit from the supplementation of Cr as an ergogenic aid to improve their overall performance. However research that has investigated the effect on acute Cr supplementation on different variables of soccer performance and predominately sprint performance utilising a soccer simulation protocol is limited (Ostojic, 2004; Mujika et al 2000; Cox et al 2002).
The Aforementioned studies have primarily focused on the effects of Cr supplementation on highly trained athletes that are competing at a high standard of competition. However no previous research has looked into the effects of acute Cr supplementation on amateur soccer players. Being as though Cr monohydrate is an immensely popular ergogenic aid not only among professional athletes but also amateur and recreational athletes, the benefit to amateur athletes needs to recognised. Previous research that has looked into the effects of acute Cr supplementation on soccer players using a soccer simulation protocol is discussed below.
Ostojic (2004) examined the effects of acute Cr supplementation (3 x 10g doses for 7 days) on 20 young male soccer players (16.6 ± 1.9 years). For the testing procedure a double blind method was used and where subjects were either administered either Cr or placebo. Subjects completed two separate trials prior and post to Cr or placebo. The testing procedure consisted of a number of soccer specific skill tests which included a dribble test, sprint-power test, endurance test and a vertical jump test. Results found that there was a significant improvement in a number of the soccer specific tests; this includes superior improvements in sprint times, vertical jump scores and the dribble test.
However no significant improvements were made on endurance performance after the two trials. Although a significant improvement was found in vertical jump performance, it is of concern to future researchers to whether the vertical jump test that was utilised during the design is a soccer specific test. During the test subjects were instructed to keep their trunk as straight as possible whilst keeping their hands on their hips to avoid contribution from the arms which doesn't successfully replicate jumping movements in soccer therefore questioning the validity of the vertical jump test as to whether or not it is a measure of soccer specific performance.
The age of the subjects in this research can also be scrutinised. Eichner, King, Myhal, Prentice and Ziegenfuss (1999) confirmed that there was insufficient research to determine the acute and chronic side effects of Cr consumption in athletes under the age of 18 therefore places the subjects which were used in the mentioned study under possible risk. Eichner et al (1999) also highlighted that Cr supplementation in young athletes could have a possible degradation of ethics, by where a 'win at all costs' mentality is fostered and an attitude by where ergogenic aids are necessary to win, which is the wrong message to be installing in young athletes.
Likewise Mujika, Padilla, Ibanez, Izquerido and Gorostiaga (2000) concluded acute Cr supplementation (20g a day x 6 days) significantly improved sprint performance and found no significant improvement in endurance performance using a soccer simulation protocol. Mujika et al (2000) also documented no increase in vertical jump performance using a similar protocol to Ostojic (2004) which has minimal significance in a soccer simulation study. Mujika et al (2000) tested 19 elite male soccer players who at the time of investigation were highly trained, however only 17 fully completed the testing due to illness or injury.
The protocol for this investigation consisted of a circuit of different exercises which consisted of a repeated sprint test (5 and 15m), vertical jump test and an intermittent endurance test. Findings in this study concluded that mean sprint times improved significantly (p<0.05) at 5m and 15m sprints times within the Cr group and also the placebo group. However one issue which causes concern in the experimental design of this study is the time of season that the testing procedure was conducted. Experimental procedures took place 3 days after the final game of the season which resulted in a drastic reduction in training load during the intervention week for the highly trained soccer player. Costill, Fink, Hargreaves, King, Thomas and Fielding (1985) and Neufer, Costill, Fielding, Flynn and Kirwan (1987) found that 7 days without training can cause a 'de-training' effect which results in a reduced ability to generate power.
This 'de-training' effect is evident for the vertical jump test as no significant improvement between the two trials was found. However if there was a significant de training effect it would have had negative consequences on other testing variables such as sprint performance, this however is not the case as sprint performance significantly improved. Mujika et al (2000) should have took into consideration a possible detraining effect when devising the experimental design as this could have negatively affect the validity of the results.
Cox, Mujika, Tumilty and Burke (2002) devised a study which tested Cr supplementation (20g a day) or placebo (20g glucose a day) on 14 elite female soccer players from the Australian institute of sport (AIS) using a soccer simulated protocol. The experimental design consisted of two trials before and after Cr or placebo over a 6 day period. The protocol consisted of fifty five 20m sprints, ten agility runs and a precision ball kicking drill which are separated by recovery walks, jogs and runs. The main findings in this study were that the average 20m sprint time in the Cr group decreased from 3.75 ± 0.19 to 3.69 ± 0.18s however this decrease in sprint time failed to reach the statistical significance level (p<0.05). Like the sprint times the average times for the agility runs failed to reach the statistical level of significance. Average times for pre and post supplementation were, respectively 10.6 ± 0.4 and 10.5 ± 0.4s. This was also the case for the precision ball kicking drill which was unaffected by the supplementation period in both groups. For the experimental design of this study Cox et al (2002) tried to standardise as many procedures as possible to reduce the variability of performance outcomes therefore increasing reliability, so that if the design was repeated the same findings would be found. This included a familiarisation trial prior to testing which enabled the subjects to be familiar with the protocol that was utilised.
Cox et al (2002) also incorporated a standardised training regime and a controlled diet for the intervention week and also scheduled testing so that it would occur at the same time of day before and after supplementation. In contrast Mujika et al (2000) failed to utilise effective standardised procedures during their experimental design. As previously mentioned Mujika et al (2000) testing procedures took place 3 days after the subject's season had finished therefore training was not standardised due to the fact that subjects had no organised training sessions during the intervention week. Mujika et al (2000) also lacked a familiarisation trial, subjects were only familiarised with the testing procedures prior to arriving for the 1st trial which could substantially affect the results. However although Cox et al (2000) standardised procedures by included a controlled diet for the subjects, it is interesting to note that one of the subjects was a vegetarian, who's Cr content is virtually zero (Greenhaff, 1997). Research has found that vegetarians respond quicker and more effectively to Cr supplementation than those who follow a normal sedentary diet and have natural muscle creatine content (Burke, Chilibeck, Parise, Candow, Mahoney & Tamopolsky., 2003; Watt, Garnham & Snow, 2004) therefore scrutinising the validity of the results. It may be of future reference to eradicate vegetarians in a experimental design which utilises Cr supplementation due to the diet implications that vegetarians have.
Soccer Simulation performance tests
To date there has been a number of soccer simulation performance tests which have been utilised to assess and measure different physiological aspects of the game (Bangsbo and Lindquist, 1992; Cox, 2002; Drust, Reilly and Cable, 2000; Nicholas, Nuttall and Williams, 2000). These protocols have been implemented so that they take into consideration different aspects of soccer performance and try to replicate the exercise patterns that are observed during match play, however due to the spontaneity of the soccer it is difficult to assess every physical or metabolic demand (Drust, Reilly and Cable, 2000). Researchers have used different protocols when investigating the metabolic and physical demands of soccer, these can documented into laboratory based protocols (Drust, Reilly and Cable, 2000; Thatcher and Batterham, 2004) and field based protocols (Bangsbo and Lindquist, 1992; Cox, 2002; Nicholas et al 2000).
Laboratory based soccer performance protocols
Drust, Reilly and Cable (2000) devised a laboratory based protocol on a motorised treadmill what represented the work rates that are observed during soccer match play. For the experimental design 7 male university soccer players (24 ± 2 years) were used and the testing consisted of three separate testing blocks which were separated by 6 days. The protocol consisted of the different exercise intensities that are utilised during soccer match play; this consisted of walking, jogging, cruising and sprinting. The speeds at which these exercises were performed on the treadmill were consistent with speeds observed by Van Gool, Van Gervan and Boutmans (1988) during a match analysis. Each testing block consisted of two 22.5 minute cycles which consisted of 23 bouts which were followed by a recovery period of 71 seconds.
During each bout the duration of each activity was as follows: walking 35 seconds (s), jogging 50.3s, cruising 51.4s and sprinting 10.5s. However in relevance to this research project it should be noted that the duration covered during the sprint bouts of the protocol of Drust, Reilly and Cable (2000) which is 10.5s does not successfully coincide with match analysis from several soccer studies that have documented the duration of sprint bouts during soccer match play. Research has found that the average sprint time during soccer match play lasts between on average two to four seconds in duration (Bangsbo, Norregard & Thorso,1991; Mayhew and Wenger, 1985) therefore concluding in some instances Drust, Reilly and Cable's (2000) laboratory based soccer specific protocol can be deemed as in valid as it fails to accurately replicate different soccer performance variables that take place in match play.
Another lab based test that was utilised to measure specific variables in soccer performance was devised by Thatcher and Batterham (2004). For this protocol six male professional soccer players were used and the testing consisted of 2x9 minute exercise bouts on a non motorised treadmill that focused on replicating different speeds, durations, distances and heart rates that occur during soccer match play. Findings from this study suggest that the protocol that was utilised induced a similar physiological load to soccer match play and can be determined as a valid measure of soccer performance.
Although lab based soccer specific protocols have been found to replicate some instances of soccer performance it is of consideration of this research project that the limitations and positives of such protocols be noted. The aforementioned lab based failed to perform a re-test procedure to conclude whether their protocols maintained reliability therefore the amount of error in each protocol cannot be determined. Another limitation of lab based testing is that due to tests being performed on treadmills, this limits the subjects to straight-line running only, therefore does not take into consideration lateral movements and agility patterns, which have found to be major characteristics of soccer performance (Bangsbo and Lindquist, 1992). These unorthodox movement patterns need to be taken into consideration when assessing soccer performance as they increase energy expenditure significantly (Nicholas et al., 2000). One positive aspect of lab based protocols are that procedures such as air temperature, equipment utilised and humidity can be easily standardised to remain constant throughout performance testing.
Nicholas et al (2000) devised the Loughborough Intermittent Shuttle test (LIST) to simulate the activity patterns during a game of soccer. The LIST consisted of two separate stages which were known as part A and part B. Part A lasted 70 minutes and consisted of five 15 minute exercise periods which were each separated by 3 minutes of recovery. Each 15 minute period involved a set pattern of intermittent high intensity running, which replicated activity patterns of a soccer match as found by Reilly and Thomas (1976). This consisted of bouts of maximal sprinting, walking, and bouts of running at speeds that corresponded to subjects VO2max at 55% and 95%. Part B of the LIST consisted of an open-ended period of intermittent shuttle running, designed to exhaust the subjects within approximately ten minutes.
The shuttle running pattern was repeated continuously until the subjects were unable to maintain the required speed for two consecutive shuttles. Results of the LIST successfully replicated total distance (12.4km) covered during a professional soccer match (Reilly and Thomas, 1976; Tumilty, 1993) and also mean heart rate was found to be similar to those found during match play (Van Gool, Gerven and Boutmans, 1988). Although these instances were found to be similar to those in a soccer match, the LIST failed to incorporate any agility movements and solely consisted of straight-line running. It must also be noted that the participants for the LIST included rugby therefore affecting the validity of the test as the physical demands of rugby may differ to those of soccer consequently scrutinising results.
Another field based soccer simulation protocol was devised by Bangsbo and Lindquist (1992). The test lasted 16.5 minutes and consisted of 40 bouts of high intensity exercise which lasted fifteen seconds and 40 bouts of low intensity exercise each lasting 10 seconds. During the high intensity bouts subjects followed a course around the edge of a penalty area on a soccer pitch which included Bouts of forward, backwards and sideways running and a agility slalom course. For the low intensity bouts players jogged into the centre of the circuit and then returned to where they finished the last high intensity bout. Unlike the aforementioned lab and field tests, the devised soccer simulation protocol by Bangsbo and Lindquist (1992) incorporates soccer specific movements (High and low intensity running, backwards movements, agility, side stepping) which replicate soccer match play, therefore showing the highest relevance to soccer performance out of all the soccer simulation protocols investigated . Utilising a soccer simulation protocol for a nutritional intervention that successfully simulates a substantial amount of the demands of soccer match will help accurately determine whether that intervention has the potential to successfully enhance soccer performance.
Eight trained male Leicestershire District League amateur soccer players ( 21.1 ± 1.5) who recreationally compete for the same team participated, all of who were physically active, and completed on average one ninety minute full size soccer match and two 1 hour training sessions per week. Prior to the investigation subjects were informed of the potential risks and then completed a confidential medical questionnaire and a informed consent form in compliance with Loughborough College Sport and Exercise Science department. The physical characteristics of the participating subjects are shown in Table 2. During each individual trial only the researcher and a supervisor were present to eliminate a competition element amongst competitors. It is also of interest that none of the subjects had a vegetarian diet.
Table 2. Physical characteristics of participating subjects (n = 8).
Modified Soccer simulation protocol
20m Sprint (A)
5m decelerate/ 5m walk
30m sprint through agility course (B) (5m between each cone)
10m Running forwards
10 running backwards
10m running forwards
Fig. 1. Diagram of the Modified Soccer Simulation Protocol (MSSP) (Bangsbo and Lindquist, 1992)
Prior to the first base line testing session subjects were instructed to attend a pre-trial familiarisation session (Cox et al, 2002). This allowed subjects to familiarise themselves with the running order of events of the modified soccer simulation protocol (MSSP) (Bangsbo and Lindquist,1992) and to raise any issues of concern with the researcher. During the familiarisation session weight, height and age of the subjects was recorded. The familiarisation trial also allowed for the researcher to undertake any alterations of adjustments which were felt to impede reliability during the intervention period.
One adjustment that was utilised in preparation for the first base line testing session were the inclusion of signs stating instructions at each station, what exercise procedure was to be executed (i.e. sprinting, walking, running backwards). Reasoning for this alteration was evident as several subjects were unclear as to what exercise procedure needed to be performed at certain stations during the familiarisation session. During the agility course of the protocol all subjects were informed that they had to touch each cone with their leading hand to enhance reliability and to minimise variability in sprint times. For this trial no results were presented to the subjects.
Upon arrival at the first testing session, body mass of the subjects was recorded and was measured to the nearest 0.1 kg. It was highlighted to subjects 12 hours prior to testing sessions to refrain from heavy physical activity, caffeine-foodstuffs and alcohol as they have been found curtail the effect of Cr (Vandenberghe, Gillis, Van Leemputte, Van Heckle, Vanstapel & Hespel, 1996). Subjects performed the MSSP between 20.00hrs and 22.00hrs which was constant for testing sessions for each individual (Cox et al, 2002; Mujika, 2000) consisting over two trials seven days apart. Each subject was instructed to perform a standardised 10 minute warm up which was consistent with exercise procedures that took place during the MSSP.
The MSSP took place on an outdoor artificial 'rubber crumb' surface and consisted of subjects completing seven full laps of the circuit. This involved seven maximal high intensity 20m sprints at point A and seven sprints at point B through the 30m agility course which was incorporated to replicate the multi-dimensional component of soccer. Total sprint distance during the MSSP was found to be similar to sprint distances found during motion analysis of a soccer match (Bangsbo et al., 1991; Mohr et al., 2003). Sprints were interspersed by different activities which were utilised by the researcher to try and replicate all aspects of soccer performance this included walking, running backwards, running forwards and lateral stepping. Each lap was interspersed by 30s active recovery period, where subjects were encouraged to keep moving in the recovery zone. Verbal feedback was given to subjects regarding time elapsed during the recovery period which involved a countdown from 5s to initiate the start of the next lap.
Each sprint was initiated by the subjects passing through a set of speed gates, which automatically started a digital timer. Trial times for the 20m sprint began when subjects passed through speed gate 1 (SG1) and the trial was completed when subjects passed through speed gate 2 (SG2). This method was also utilised for the 30m agility course. Timing for the agility course was initiated when subjects passed through speed gate 3 (SG3) and completed when subjects passed through speed gate 4 (SG 4). Timing for the recovery period was initiated when subjects entered the recovery zone and this was monitored by the use of a hand held stopwatch. During the recovery period subjects were encouraged to keep active.
A random selection process then allocated subject pairing to a creatine (n = 4) or placebo (n = 4) treatment group. The supplementation 'loading' phase which was attributed by Hespel, Maughan and Greenhaff (2006) was utilised and commenced one day after the initial baseline trial and was terminated one day before the post intervention session. The creatine group members each ingested 5g of powdered creatine (Body Fortress, creatine monohydrate), four times daily, for seven days. The placebo group ingested a similar protocol of 20g of maltodextrins, 4 times daily for 6 days. The supplementation process that was utilised was conducted in a single blind manner to control for the placebo effect, it must also be noted that there was no researcher bias upon administering supplementation.
The supplement was mixed into approximately 200ml of flavoured water to disguise taste and texture differences (Mujika et al., 2000). Subjects were instructed to consume the supplement with morning, mid-day afternoon and evening meals. Each individual supply of supplement was carefully measured and individually packed into re-sealable sandwich bags and issued to the subjects for the duration of the trial. Subjects were also administered a sufficient supply of flavoured water to consume with the supplement for the intervention week. To ensure compliance of supplement consumption, subjects were instructed to return empty sandwich bags at the end of the intervention week.
Data was analysed using SPSS for Windows version 15.0 (SPSS, Inc., Chicago, IL). All data presented in the text, tables and figures are represented using mean values. Two, paired sample t-tests for mean were conducted to challenge the experimental hypothesis for the 20m sprints and agility sprints for all subjects. The paired samples t-tests will utilise mean sprint times for pre and post intervention scores, to conclude whether or not a significant difference in sprint times has been achieved between the two trials. The experimental significance level was set at P<0.05.
All subjects successfully completed the creatine (n = 4) or placebo (n = 4)supplementation protocol. None of the subjects that participated in the study reported any side effects throughout the intervention week.
Analysis of intervention – 20m sprint
Sprint performance of 20m sprint trials is demonstrated for both creatine and placebo groups and is illustrated in fig.3 and fig.4.
Fig.3. Subject mean pre-intervention and post-intervention 20m sprint trials in the creatine group (n = 4)
All subjects improved mean 20m sprint times within in the creatine group after supplementation. The overall mean 20m sprint time for all subjects within the creatine group decreased from 2.99s ± 0.12s to 2.84 ± 0.09s respectively, however this improvement failed to reach statistical significance (p < 0.44).
Fig.4. Subject mean pre intervention and post intervention sprint trials in the placebo group (n = 4).
The placebo group failed to demonstrate any significant difference between pre-supplementation and post supplementation 20m sprint times (p < 0.76) with only one subject recording a minor improvement (0.05s). The average mean sprint time for the placebo group showed no significant changes, with average sprint times only fluctuating within a 0.12s range pre and post intervention.
Analysis of intervention – agility sprint
Sprint performance of agility sprint trials is demonstrated for both creatine and placebo groups and is illustrated in fig.5 and fig.6.
Fig.5. Subject mean pre-intervention and post intervention agility sprint trials in the creatine group (n = 4)
Two subjects improved mean agility sprint times within the creatine group after supplementation with subject C7 demonstrating an improvement of 0.13 seconds respectively. The mean average sprint time for the entire creatine group decreased from 7.18s ± 0.53s to 7.15s ± 0.46s, however this slight improvement in agility sprint time failed to reach statistical significance (p = 0.50).
Fig.6. Subject mean pre-intervention and post-intervention agility sprint trials in the placebo group.
The placebo collection group failed to show any significant improvements in sprint times between pre and post supplementation testing sessions (p< 0.85). The average agility sprint time for the placebo group demonstrated a slight increase between pre and post intervention testing sessions. Mean sprint times increased from 7.18s ± 0.55s to 7.20s ± 0.48s, thus showing no significant value.
Findings from this research study signify that creatine supplementation demonstrates no significant improvement in performance during high intensity, repeated straight line sprints, and agility sprints of trained amateur soccer players. The acquired data demonstrates that no significant difference in sprint performance was evident in placebo and creatine condition groups, following an acute, 6 day supplementation period. Although an improvement in performance was apparent for all subjects in the creatine group during 20m sprint bouts, the required level of experimental significance was not reached ( p = 0.44). Similarly the placebo group did not significantly improve sprint performance post treatment on account of their being no significant difference between pre and post intervention trials ( p = 0.76). Acute creatine supplementation also failed to report any significant ergogenic effect on repeated agility sprints. It was demonstrated that no statistical significance could be identified in both creatine and placebo groups, with the creatine group only demonstrating a slight increase in agility sprint performance.
Findings from this study supports research demonstrating that Cr supplementation has no ergogenic effect on repetitive, high intensity running performance in soccer players (Redondo et al., 1996; Smart et al., 1996). Conversely recent research discard findings from this study declaring creatine supplementation can improve repetitive, high intensity sprinting bouts for soccer performance (Cox et al., 2002; Mujika et al 2000; Ostojic, 2004).
The Cr supplementation protocol of 20g/d for 6 days that was utilised for this study has been repeatedly demonstrated as a successful protocol to increase Cr and PCr muscle content (Ahmun, 2005; Hultman et al., 1996). A limitation of the study protocol was the inability to directly measure Cr muscle content within subjects. This would verify whether compliance of Cr ingestion was maintained throughout the intervention week as a higher Cr concentration would be evident. Compliance of Cr ingestion for this study was indirectly measured by ensuring subjects returned empty sandwich bags in which supplementation was distributed. However this method cannot verify that Cr ingestion within subjects did in fact occur. Mujika et al (2000) utilised a urine sample collection process, which enabled the researcher to identify whether Cr urinary content increased therefore compliance of Cr ingestion could be identified throughout the intervention week.
Acute Cr supplementation has been found to increase body mass by up to 2kg (Balsom et al., 1995; Becque et al., 1997). A limitation of this research study can be identified as post supplementation body mass failed to be measured. If an evident increase in post intervention body mass was measured within subjects, it could be therefore suggested that compliance of Cr supplementation was successful. However this can only be identified as a inconclusive assumption as increases in body mass post Cr supplementation could be identified from external factors such as dietary habits, general health and hydration status (Poortmans & Francaux, 2000). Although post intervention body mass was not recorded for subjects, an indirect assumption can be made that increases in body mass could be rationale for sprint times showing no significant improvement within the creatine group. This can be supported by Balsom et al (1994) who identified that increases in body mass from acute Cr supplementation to have a counter productive effect on activities that require fast and efficient movements such as sprinting.
The total time it took each subject to complete 7 laps of the MSSP lasted approximately 11-12 minutes. Despite using a soccer simulation protocol for this study it should be noted that total duration does not coincide with total duration of a soccer match (90 minutes). Therefore a true reflection of the influence of Cr, during a full length soccer match cannot be determined. However to gain full compliance from coaches for subjects to complete a 90 minute protocol, from a team that were currently in the competition phase of a season was simply not feasible due to the possibility of injury or overtraining. It should also be noted that the motivation levels of subjects needs to be considered.
The importance of moving backwards, sideways and having the ability to change direction are highlighted by Reilly, (1997), who states that approximately 16% of the distance covered during soccer match play involves such movements. This therefore is an advantageous aspect of the MSSP, which takes all the aforementioned components of soccer performance into consideration. However Ostojic (2004) and Mujika et al (2000) failed to utilise the multi-dimensional aspects recognised by Reilly (1997) when using a soccer simulation protocol, therefore an assumption can be made that such research fails to fully replicate many aspects of soccer performance, questioning findings found by such researchers. Another positive of the MSSP is that is successfully replicates total sprint distances covered during soccer match play.
Bangsbo et al (1991) and Mohr et al (2003) reported that the total average sprint distance found during soccer match play to be between 343m to 771m. Total sprint distance for the MSSP is 350m, determining the MSSP as valid measure of soccer sprint performance. Another additional strength of the MSSP was its suitability of being conducted on an outdoor surface. Bangsbo (1994) stated that intermittent field tests append important data to that which can be utilised from conducting physiological testing in laboratory conditions. However there are a number of limitations to utilising a field test. Although the MSSP successfully incorporates a vast amount of soccer components, a limitation is that it fails to integrate soccer ball-skill activities.
An additional limitation for this study can be contributed by Dawson et al (1991). The author proposed that athletes may 'pace' themselves to ensure completion of high intensity tests such as the MSSP. As to delay fatigue athletes control effort through pacing, to ensure that PCr and ATP are not prematurely exhausted. This leads to athletes avoiding fatigue early to ensure completion of such tests (Dawson et al., 1991). However if this pacing effect is apparent, a true reflection of an athletes sprint performance cannot be determined as maximal effort will not be reached for each sprint.
Prior to administration of creatine or placebo,subjects were informed of any potential side effects that could occur from Cr ingestion during the intervention week. This included side effects that have been established in research such as body mass, and anecdotal side effects such as muscle cramping, dehydration or gastro-intestinal problems. However disclosing this information to subjects may have had a negative effect. This concerns whether the subjects were in fact truly blind to their treatment group. Although post supplementation body mass was not recorded for subjects, if subjects realised any increases in body mass throughout the intervention week, it would lead them making an assumption to which treatment group they had been assigned.
Another possible assumption for the limited potential of Cr during this study is the trained status of the subjects. The experimental testing of this study took place during the competition phase of the season. Subjects were training twice a week and playing up to two 90 minute matches, which could lead to a possible assumption that subjects had high Cr concentrations prior to the study therefore limiting the ergogenic effect of Cr on sprint performance. This assumption can be supported by Cox et al (2002) who failed to find any significant difference in 20m sprint performance within trained subjects through acute Cr supplementation during the competition phase of the season.
One major criticism of this study is the small sample size that was utilised leading to low statistical power. This occurred due to constraints placed on the researcher by factors such as injuries of players and non attendance to the first testing session. Tarnpolsky & McLennan (2000) concluded that a sample size of at least 15 subjects is required to achieve statistical power within a study. This statement recognises that most studies that have tried to determine the ergogenic potential of Cr on sprint performance on soccer players demonstrated low statistical power. For future investigation demonstrating the effects of Cr, the work of Tarnpolsky & McLennan (2000) should be taken into consideration where a sample size of at least 20 subjects should be utilised to increase statistical power and significance.
In summary, taking into consideration the aforementioned limitations of this study, acute creatine supplementation does not possess any significant potential ergogenic enhancement of repeated high intensity sprints of trained male amateur soccer players. Constraints of the study included lack of controllability over external factors such as lifestyle constraints which include dietary and sleep patterns and also environmental factors. Areas for review for future directions include, utilising a larger sample size to enhance statistical power and also incorporating a method of directly measuring Cr muscle content pre and post intervention to ensure supplementation compliance is adhered to. Further areas to consider include utilisation of a protocol which successfully replicates and tests all components of soccer performance during a 90 minute match play scenario. This would incorporate not only sprinting but the replication of ball skill work, jumping, movement patterns and general soccer skills which are essential for soccer performance. This would therefore assist with the clarification of the ergogenic potential of Cr supplementation for elite, amateur and recreational soccer players alike.
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