Effect of CR Supplementation on Athletic Performance
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Published: Tue, 20 Feb 2018
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 2×9 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 pe
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