Cutting Edge Research: Age Effect At The U17 World Cup

Is there an advantage to being born in the early part of the year? The relative age effect means that if you are born close to the cut-off age for a competition; you are more likely to be selected for the team than if you are born later in the year. This phenomenon seems to occur at all levels of play from local travel teams to the most advanced youth competitions. A new study published in the Scandinavian Journal of Medicine and Science in Sports shows that in nearly all countries participating in the U17 World Cup, there is a strong relative age effect. In fact, nearly 40% of the players are born in the first three months of the year while only 16% are born in the last quarter.

In this study, the rosters of all teams participating in the last six U17 World Cup competitions were obtained from FIFA. The player birthdates were recorded and analyzed to determine of there was a trend for players to be born in one part of the year versus another.

The first figure shows the percent of players born each month. It’s easy to see that there are far more players born in the early part of the year than in the later. This trend holds for all six competitions, and for all of the FIFA regions except Africa (more on this later). Also, the most and least successful teams showed similarly strong age-effects.

Several previous studies into the relative age-effect show that in many youth sports, it is advantageous to be born near the cut-off date for a give competition. For international soccer competitions (e.g. U17 World Cup), that cut-off date is based on the calendar year. For American youth soccer, that date is associated with the American school year, July 31.

Studies show that the relative age-effect most often occurs because coaches who select players for advanced training or competition typically use physical and psychological maturity as a major indicator of performance. Thus, those players with early birthdates tend to be bigger and faster than those born later in the year. As discussed previously on the Science of Soccer Online, this may have dramatic consequences for player development (click here). Potential players with late birthdates are being overlooked at a young age simply because they are not as physically mature. They are then denied the developmental opportunities that their older counterparts are offered. As a result, the talent pool for national teams, especially at the U17 level, may be diminished.

Back to the African countries... The African region showed a much different patters of birth month distribution that the other regions. For the African teams, in particular, the western African countries of Ghana, Nigeria and Togo, showed a reverse age effect. That is, more players were born in the later part of the year than in the early months. 14% of the African players were born in December. Also of all underage players participating in the tournament, 41% were on African team rosters. The second figure clearly shows the spike in African birth dates in December of the competition year. Contrary to other regions, in Africa, it seems to be more advantageous of be born in the late in the year rather than early.

It’s not clear why the African teams show this trend. One explanation is that the African teams manipulate birth certificates in order to make older players eligible for competition. It is also possible that there are legitimate errors on African players’ birth certificates. According to UNICEF, many African births are not registered. That is, many African children are not issued a birth certificate when born. For many kids, birth certificates are issued years after birth. In these cases, parents often guess the actual birthdates. So, it’s not surprising that some player’s birthdates might be clustered in a single month.

The bottom line, even at the highest level of youth competition, the FIFA U17 World Cup, the relative age effect exists. Whether this is the result of long-term trends in the player selection process or the training environment provided for older players is not known. In either case, there are several negative outcomes for excluding potentially exceptional players based on their relative age and maturity.

Reference:

Williams JH (2009) Relative age effect in youth soccer: analysis of the FIFA U17 World Cup Competition. Scandinavian Journal of Medicine & Science in Sports. In press, DOI:10.1111/j.1600-0838.2009.00961.x
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Getting a Bigger Bang for Your Training Buck?

Coaches and athletes are constantly searching for ways to improve fitness. Endurance and interval training are the most often used. However, these programs usually require a time commitment of 30-00 minutes per day. This time commitment makes it difficult, if not impossible, to incorporate endurance training into a typical practice session. Researchers at McMaster University have found that a program brief, high intensity exercise might actually improve fitness more than a traditional endurance training program. This program requires only 2-3 minutes of exercise per session – a much bigger bang for the training buck. But, can this type of training be effectively used by soccer players?

In a series of studies headed by Dr. Kirsten Burgomaster, the researchers asked their subjects to perform a very small number of very high-intensity bouts of exercise. The high-intensity training groups used a stationary bicycle and performed 30 seconds of all-out, supra-maximal exercise - they pedaled as hard as they could for 30 seconds. They then rested for 4 minutes and repeated the bout 4 to 6 times. This was done 3 times per week for either 2 or 6 weeks. For comparison, an endurance training group cycled continuously for 40-60min per session, 5 times per week.

After only two weeks of training (only 6 sessions), the high-intensity group, doubled endurance time. That is, they exercise for nearly twice as long before reaching exhaustion. They also improved time-trial performance by 10%. The endurance group showed little to no improvement. After 6 weeks the high-intensity group showed several important biochemical changes within the muscle, such as glycogen, phosphocreatine levels and metabolic enzyme activities. Interestingly, laboratory measures of “fitness” such as VO2max and exercise heart rates were not improved.

A key difference in the two training groups was the amount of time spent training and the total amount of work performed. Training for high-intensity group required about 2-3 minutes of actual exercise compared to 60 minute for the endurance group. Including recovery, the high-intensity session lasted ~20 minutes. Also, the high-intensity group performed about half as much total work as the endurance group. The bottom line is that high-intensity training resulted in greater improvements with less time and work.

As a coach, it’s easy to see how this type of high-intensity training would be a tremendous benefit for improving fitness when practice time is limited. The big question is, should coaches consider using this type of training with their players? Instead of using an exercise bike, players could do repeated 30 second sprints (or 200-300 meter sprints) with a 4 minute recovery. However, there are a few things to consider before abandoning traditional training. First, the researchers are quick to point out that they don’t know for sure if high-intensity training provides all of the cardiovascular, metabolic and muscular benefits that traditional endurance training does. It’s also not known if the improvements are long lasting. Second, it’s not known if the improvements found in these studies will translate into improved fitness over the course of a 70-90 minute match. This is particularly important when one considers the stop-start, run-sprint nature of soccer. Third, and most importantly, cycling is much different than running when it comes to impact forces on the knee, ankle and hip. Using high-intensity running during training might increase the risk of orthopedic, over-use injuries, especially in young athletes. At the very least, players should be allowed a day or two to recover from each training session.

For now, this series of studies raises some very interesting ideas regarding training. They may ultimately cause us to re-think how we go about fitness development. However, much more work needs to be done to determine of high-intensity training is appropriate and effective for young footballers.

Note: Many thanks to Dr. Don Kirkendall of the FIFA Medical Assessment and Research Centre for suggesting this topic.

References:

Gibala MJ, McGee SL (2008) Metabolic adaptations to short-term high-intensity interval training: A little pain for a lot of gain? Exercise and Sports Sciences Reviews, 36:58-63.

Burgomaster KA, Howarth KR, Phillips SM, Rakobowchuk, MacDonald MJ, McGee SL, Gibala MJ (2008) Similar metabolic adaptation during exercise after low volume sprint interval and traditional endurance training in humans. Journal of Physiology, 586:151-160.

Gibala MJ, Little JP, van Essen M, Wilkin GP, Burgomaster KA, Safdar A, Raha S, Tarnopolsky MA (2006) Short-term spring interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. Journal of Physiology, 575:901-911.

Burgomaster KA, Heigenhauser GJF, Gibala MJ (2005) Effect of short-term sprint interval traiig on human skeletal muscle carbohydrate metabolism during exercise and time-trial performance. Journal of Applied Physiology, 100:2041-2047.

Burgomaster KS, Hughes SC, Heigenhauser GJF, Bradwell SN, Gibalb MJ (2004) Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans. Journal of Applied Physiology, 98:1985-1990.



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No Place for Alcohol

One of the time-honored, post-match traditions of adult league soccer leagues is to head to the pub and have a pint or two (or three). Many believe that beer and other alcohol-containing drinks actually aid recovery. The argument is that alcohol is a carbohydrate and carbohydrates help replenish energy stores. In fact, some athletes jokingly refer drinking beer as “carbohydrate loading”. Unfortunately, research clearly shows that drinking alcohol after exercise does not aid in recovery. In fact, beer and other adult beverage can dramatically impair the recovery process by affecting muscle damage, energy replenishment and re-hydration.

A new study published in the Journal of Science and Medicine in Sports emphasizes this point. The researchers examined the effect of post-exercise alcohol consumption on markers of muscle damage and soreness. They asked their subjects perform a strenuous bout of exercise which was followed by a meal. One group drank orange juice (control) while the alcohol group drank orange juice mixed with vodka. For this group the total amount of alcohol consumed was equal to 8-9 standard drinks.

At 36 and 60 hours after exercise, muscle force produced by the alcohol group was considerably lower than the control group, 15-20% lower. Those in the alcohol group also reported higher ratings of muscle soreness and the 36 and 60 hour measures. Diminished muscle performance and increased pain, clearly two strikes against alcohol.

The investigators explained that the alcohol consumption after exercise likely magnifies the amount of muscle damage that is typically associated with strenuous activity. The type of muscle damage that leads to muscle soreness typically occurs in several stages (see The Painful Truth About Muscle Soreness). The first occurs during exercise. The second occurs immediately after exercise and the process usually last for several hours. This is the process that seems to be increased by alcohol , possibly through its negative effects on the immune system and inflammation. Whatever the cause, it’s clear from this study that the effects of drinking after exercise can literally be felt for several days.

The conclusion that alcohol is not a good recovery drink is supported by several earlier studies. These studies show that consuming alcohol after exercise adversely affects energy replenishment. Drinking after a match can impair the metabolism of carbohydrates which leads to reduced blood glucose levels and diminished replacement of muscle glycogen. In addition, consuming alcohol-containing drinks typically reduces the intake of other carbohydrates that are essential to recovery. As discussed previously on the Science of Soccer Online (link), restoration of muscle glycogen is possibly one of the most important aspects of recovery. Thus, from metabolic point of view, drinking after a hard match can prevent the muscles from replenishing much needed energy stores. Despite it being a carbohydrate, it actually hinders recovery.

Alcohol is also a potent diuretic that causes fluid loss through urination. It makes sense that drinking after a match can lead to further dehydration. Much of the fluid that is being consumed through alcoholic beverages is also being excreted. Research has shown that anything containing 4% or more alcohol can lead to further dehydration after exercise. By way of comparison, anything other than light beer contains more than 4% alcohol.

So, despite the popular belief that beer and other adult beverages help recovery from exercise, the scientific evidence clearly shows otherwise. Alcohol consumption after strenuous exercise 1) intensifies delayed-onset muscle soreness, 2) impairs muscle glycogen replenishment and 3) hinders re-hydration. So, hoisting a few pints after a hard match can leave the player in poor condition of play the following day. The bottom line... there is no place for alcohol after exercise.

References:

Barnes MJ, Mundel T, Stannard SR (2009) Acute alcohol consumption aggravates the decline in muscle performance following strenuous eccentric exercise. Journal of Science and Medicine in Sports, in press (doi:10.1016/j.jsams.2008.12.627)

Burke LM, Collier GR, Broad EM, Davis PG, Martin DT, Sanigorski AJ, Hargreaves M (2003) Effect of alcohol intake on muscle glycogen storage after prolonged exercise. Journal of Applied Physiology, 95:983-990.

Heikkonen E, Yilkahri R, Roine R, Valmaki M, Harkonen M, Salaspuro M (1998) Effect of alcohol on exercise-induced changes in serum glucose and serum fatty acids. Alcohol Clinical and Experimental Research, 22:437-443.

Shirreffs SM, Maughan RJ (1997) Restoration of fluid balance after exercise-induced dehydration: effects of alcohol consumption. Journal of Applied Physiology, 83:1152-1158.

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Cutting Edge Research: A New Way to Drink Sports Drinks

For years, sports drink companies such as Gatorade® and Powerade® have extolled the benefits of their products. They argue that sports drinks can replenish energy, electrolytes and fluid lost during exercise. The scientific community has largely shown that this is in fact the case. Sports drinks can play a key role in the recovery from prolonged exercise. However, there may be an added benefit of sports drinks and athletes might consider a new way to drink them. A new study shows that these beverages may also have short-term effects on the central nervous system – but only if they are consumed correctly.
A group of researchers from Ghent University in Belgium examined whether or not simply rinsing the mouth with a sports drink affects endurance performance. Twelve trained cyclists participated in four exercise trials. For each trial they were asked to complete a certain amount of work in as short of time as possible. The trials were designed to last about 60min.

Before and during each trial, the athletes were given either a sports drink (Gatorade) or an artificially sweetened placebo. For two of the trials, they took in ~120ml (~4 ounces) of the beverage, rinse it in their mouth for 5 second then spit it out. For the other two trials, they drank an equal volume of Gatorade or placebo.

The time needed to complete the ride was significantly lower when the Gatorade was used as a rinse compared to when the drink was actually consumed. Under the sports drink rinse condition the cyclists completed the ride in 61:42 compared to a mean time of 63:16, an improvement of almost 4%. This occurred despite slightly lower blood glucose level and blood lactic acid concentration. It appears that simply rinsing the mouth with a sports drink for ~5 second causes a diminished perception of effort for a given exercise intensity. That is, the riders could exercise harder for the same degree of discomfort.

The researchers point out that actually drinking the Gatorade did not affect endurance performance while rinsing the mouth did. This is intriguing since most experts would have expected the opposite to be true. It also means that something must be happening in the mouth rather than that through digestion. It is possible that the carbohydrates in the sports drink interact with some sort of “receptors” in the mouth to stimulate the central nervous system. This effect might, in turn, improve the athlete’s effort and aid performance. While this is speculation on behalf of the researchers, there is some logic in their idea.

As for soccer players drinking sports drinks, it probably not advisable to rinse and spit as was done in this study. Ingesting both carbohydrates and fluids are critically important during recovery and for avoiding dehydration. However, athletes should consider that gulping their Gatorade may not be the best approach. The might try taking a drink, holding it in the mouth for 5 second before swallowing. This might maximize the short-term effects on the central nervous system as well as benefit from the long-term effects on energy storage and hydration. In the end, holding your drink in your mouth for a few seconds before swallowing might provide a small edge during the match.

References:

Pottier A, Bouckaert J, Gillis W, Roels T, Derave W (2008) Mouth rinse but not ingestion of a carbohydrate solution improves 1-h cycle time trial performance. Scandinavian Journal of Medicine and Science in Sports, DOI: 10.1111/j.1600-0838.2008.00868.x

Carter JM, Jeukendrup AE, Jones DA (2004) The effect of carbohydrate mouth rinse on 1-h cycle time trial performance, Medicine and Science in Sports and Exercise, 36:2107-2111.
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Penalty Kicks… By the Numbers

Penalty kicks are a critical time of decision making for both the goal keeper and the penalty taker. Given that, for most professional games, the average number of goals scored is around 2.5, a penalty kick can have a major influence on the outcome of a match. Penalty kicks may reach speeds near 125 mph and is usually over within a quarter of a second. Thus, the goal keeper must make a decision on how to stop the shot before the ball is struck. Statistics show that goal keepers will most often jump to the left or right, hoping to guess correctly and place him (or her) self in a position to block the kick. Is this action by the keeper the best strategy? Research headed by Michael Bar-Eli at the Ben-Gurion University of the Negev in Israel makes some interesting conclusions about how goal keepers should defend penalty kicks.

The researchers analyzed the video of 286 penalty kicks from professional leagues in Europe and South America as well as from the European Championships and World Cup competitions. They coded each PK into one of three vertical (high, middle or low) and horizontal (right, center or left) directions. Shots that missed the goal were not included in these analyses. They also coded goalkeeper movements (jump right, jump left or stay central) and whether or not they stopped the shot. Using simple statistics, they compared the success of goalkeepers in stopping shots based on their movements and where the ball was placed.

From the penalty kicker’s standpoint, 85% of the penalty shots placed on goal were successful. A bit more than half of the shots taken were placed in the lower one-third of the goal (57%). These low attempts were successful ~80% of the time. By comparison, only 13% of shots were placed in the upper third of the goal. However, all of these efforts resulted in a goal scored (100% success).

Slightly more shots were placed to the goal keeper’s right side compared to the center or left. Of these three directions, kickers were most successful when shooting at the center of the goal. Shots aimed at the center of the goal were successful 87% of the time compared to an 83% success rate for shots placed at the outer thirds of the goal.

Based on these numbers, professional penalty kick takers most often place the ball at the lower right corner of the goal (40% of attempts). However, they are far more successful when shooting at the upper portion. Thus, the most successful strategy for the penalty kick taker is to place the ball in the upper third of the goal area rather than the lower portion. Assuming that the shot doesn’t go over the crossbar, placing the shot in the upper region of the goal will almost insure a successful attempt.

Goal keeping behavior explains part of the goal scoring successes. In attempting to stop the penalty kick, goal keepers jump to the right or left 94% of the time. In doing this, they guess correctly only about 40% of the time (i.e. jump left, shot placed left). However, even when they guess correctly, they only stop 25-30% of the shots. The most intriguing part of the Dr. Bar-Eli’s analyses is that when goal keepers remain in the center of the goal and the shot is placed in the center, they make the save 60% of the time. Given that about 30% of penalty kicks are placed in the center third of the goal, remaining stationary in the center of the goal increases the keepers chances of stopping the shot from about 13% to more than 33%.

Thus, the best strategy for goal keepers is to remain in the center of the goal during the penalty kick. Thus the idea that goal keepers should jump left or right and hope they guess correctly is not supported by these numbers.

Why might there be more success when the goal keeper stays in the center of the net? When a keeper jumps in one direction, he/she is only able to cover about 1/9 of the goal area (usually the lower corner) plus a bit of the central area. Thus, if the ball is placed in the side or upper third, the keeper has very little chance of stopping the shot. The keeper is either out of position of in a poor position to stop the shot. However, if the keeper remains in the center of the goal area, he/she can cover closer to one third of the goal area (the upper-, middle- and lower-central areas).

If these numbers are correct, then why do goalies jump left or right in their effort to stop penalty kicks? Part of the decision may be based on experience, reading the shot taker’s body language and to opinion that diving is indeed the best strategy. Another reason probably lies in the concept of a “bias towards action”. This occurs with a decision is based on perceived need to “do something” rather than nothing. In sports, it is often said that mistakes are more forgivable if they are made at full speed. Diving to the left or right gives the appearance of effort and avoids the perception that he/or she didn’t attempt to make a save. In fact, a survey of goal keepers show that the vast majority feel worse if a goal is scored when they remain central versus diving to the left or right.

The take home message is that from a statistical standpoint, it may be more advantageous for a goal keeper to defend a penalty kick by remaining in the goal’s center rather than diving to one side. Despite the need to make a heroic effort, this situation may require doing less rather than more.

References:

Bar-Eli M, Azar OH (2009) Penalty kicks in soccer: an empirical analysis of shooting strategies and goalkeepers preferences. Soccer & Society, 10:183-191.

Bar-Eli M, Azar OH, Ritov I, Keidar-Levin Y, Schein G (2007) Action bias among elite soccer goal keepers: the case of penalty kicks. Journal of Economic Psychology, 28:606-621.
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The Role Soccer Clubs Can Play in Promoting Healthy Lifestyles

It is clear that a growing health concern in the US and many other countries is the increasing incidence of obesity and related diseases. Over the past few years, the number of children and adolescents who are classified as overweight and obese has increased dramatically. Unfortunately, statistics show that these children will very likely grow up to be obese adults with a whole host of associated health issues such as hypertension, diabetes and orthopedic problems. A large contributor to this problem is the lack of regular physical activity.

Soccer clubs are in a unique position to combat what is now considered a health crisis. Soccer offers individuals of all ages the opportunity to engage in regular exercise through structured programs and within a social network. Soccer can also help kids develop skills and habits that can lead to a healthier adulthood.

Most soccer programs offer youth players the opportunity to exercise anywhere from two to five days per week. Practice sessions usually involve components of fitness (running), strength training (stopping, starting and cutting maneuvers) and motor skill development (ball control). Soccer also provides a social network for those involved. Whether a competitive or recreational team, players exercise together. Indeed, soccer is one of the best activities for promoting fitness in children and adolescents. Also, organized leisure-time activates, including sports, is associated with improved health, academic achievement and better social adjustment (Mahoney et al, 2006).

This concept can bee seen on almost any soccer field. Young kids are exercising, laughing and playing with their friends. At the end of the session, many are sweating and out of breath, smiling from ear to ear and asking when they can practice again. It’s this love of the game and enjoyment for exercise that is the key to promoting fitness.

The immediate health benefits for young players are obvious. However, the real benefit of playing may not appear until adulthood. That is, kids who play youth sports are far more likely to engage in physical activity as adults. They are more likely to develop a life-style that will help avoid weight gain and all of its associated problems.

Here are a few findings from the research community:

Participation in sports clubs at young ages increases the odds of being physically active later in life by 5- to 6-fold (Aarnio et al., 2002).

Participation in sports twice or more per week at age 14 is associated with a high level of physical activity at age 31 (Tammelin et al., 2003).

The amount of time 35 year old spend exercising is correlated with the amount time spent in organized physical activity programs at ages 10-12 (Trudeau et al., 2004).

Children who continue with a sports program through their adolescent years are more likely to exercise as young adults than children who drop out at an earlier age (Kjonniksen et al, 2008).

The conclusion is that the longer children participate in organized sports programs, the more likely they are to develop a habit of exercising as an adult. Given this, soccer clubs are in a position to play a key role in improving the health of future adults. Based on this, the European Union has emphasized the important role that sports clubs can play in promoting life-long physical activity. They feel that the sport as a tool for promoting health and physical activity has a greater influence on children, teens and young adults that any other activity or program. They also feel that sports clubs are one of the more under-utilized pathways to a healthier lifestyle. At a time when physical education in the schools is being reduced or even eliminated, it is important for sports clubs to fill the exercise void.

A key age for developing life-long exercise habits seems to be around 15-16 years old. It is at this age that sports programs have the largest drop rate. During the mid-teen years, adolescents find more academic and social activities, many enter the part-time work force and some lose their enjoyment of the sport. If clubs can keep kids active through their teen years, the impact on their adult exercise habits is much greater.

So, what is needed to capitalize on the health promotion benefits of youth soccer?

First, clubs should offer programs for kids of all abilities from novice to expert, from young to old. There should be opportunities for completive athletes as well as those who “just want to get in some exercise”. Most importantly, players should develop an enjoyment for the game and an appreciation for being fit and healthy.

Second, all programs should stress and promote the role of physical activity in maintaining a healthy lifestyle. This includes emphasizing both exercise and diet in maintain one’s fitness level. Not only will these two aspects improve fitness of the recreational player but it will increase performance of the competitive athlete.

Third, clubs should offer multiple opportunities and varieties for participation. The objective is for kids to continue participation without the program growing stale. Many participants in youth sport programs drop out around age 15-16. Offering new and exciting programs at this age will help avoid boredom and burn out that often accompanies “doing the same thing over and over”.

It is clear that youth soccer clubs can play a key role in promoting a healthy lifestyle. By instilling a life-long enjoyment of exercise and proper diet, soccer clubs can improve fitness in youth and help instill habits for a healthy adulthood.

References:

Aarnio et al. (2002) Stability of leisure-time physical activity during adolescence – a longitudinal study among 16-, 17- and 18-year-old Finnish youth. Scandinavian Journal of Medicine, Science and Sports, 12:179-185.

Kjonniksen et al (2008) Organized youth sport as a predictor of physical activity in adulthood. Scandinavian Journal of Medicine, Science and Sports, 18: 1-9.

Mahoney et al. (2006) Organized activity participation, positive yoth development, and the over-scheduling hypothesis. Social Policy Report, 20:3-32 (by the Society for Research in Child Development, National Academy of Sciences).

Tammelin et al. (2003) Adolescent participation in sports and adult physical activity. American Journal of Preventative Medicine, 24: 22-28.

Trudeau et al., (2004) Tracking o f physical activity from childhood to adulthood. Medicine, Science and Sports in Exercise, 36:1937-1943.
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Science of Soccer Online Meets Facebook®

The Science of Soccer Online now has its own Facebook® page. Join in, become a fan and keep updated with the latest info on soccer training, nutrtion, injury prevention and psychology.

Click Here to become a fan.

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Cutting-Edge Research: Can Cold Baths Help Recovery?

Many club and college teams routinely use cold water immersion after matches or intense training days. Studies have shown that cryo- or cold-therapy can prevent or reduce exercise-induced muscle damage and muscle soreness. Rather than applying icepacks to different muscle, sitting in a cold bath will accomplish he same effect. But is this treatment really effective? Will cold water immersion prevent muscle damage? Will it improve performance the next day? These questions were addressed in a recent study conducted by a group of Australian researchers.

Several earlier studies indicate that cold-water immersion does help alleviate muscle soreness in the days following intense exercise. It also aids in restoring lost performance. When intense exercise is performed, it can cause micro-damage to the muscle fibers. This injury initiates a cascade of events leading to further damage and resulting in soreness, stiffness and loss of performance (see “The Painful Truth About Muscle Soreness”). By quickly cooling the muscle, immediately after exercise, this process can be arrested and much of the next-day soreness can be avoided.

Unfortunately, most of the earlier studies use a single bout of exercise followed by cold water immersion. They did not ask their subjects to repeat the exercise bout over the following days. This made it difficult to apply the results to a soccer season where players train or play matches on a daily basis. To address this, Dr. Greg Roswell and colleagues used a simulated soccer tournament where players played daily matches over a four-day period. The goal was to simulate a tournament situation.

Two groups of junior player (age 16 years) took part in the four-day study. They were divided into two groups, one that under went 10min of cold water immersion (10º C or 50º) immediately after each match and one that under went immersion in a bath near body temperature (34º C or 93º F). The players all played one match per day for four days. About 90min before each match, they performed several physical performance tests that included repeated sprint and vertical jump tests. Blood samples were also drawn and analyzed for markers of muscle damage.

The researchers found that the cold water immersion did not improve any of the sprint or vertical jump values. Nor did it affect any of the markers of muscle damage. However, the cold treatment did reduce the players’ perceptions of muscle soreness and fatigue. In fact, all of the players using the cold water immersion felt that it was beneficial and aided their recovery between matches. Only one of the players in the other group felt that way.

Based on there results, the investigators concluded that cold water immersion after matches played on successive days did not benefit performance or prevent muscle damage. It did, however, have positive effects on the player’s feelings of muscle soreness and fatigue.

While this is an excellent study, the main criticism is that there were no measures of match performance or fatigue experienced within the match. The performance tests were given before each day’s match was played. A lower perception o f pain and fatigue can improve a player’s confidence and play on the field. It may also reduce the perception of fatigue at the end of the match. Also, any positive effects of cold water immersion on the body might not be noticeable until late in a match when fatigue begins to affect play.

A quick (and very non-scientific) survey of the Virginia Tech men’s soccer team confirmed what the researchers found about perception. Nearly all of the players asked readily agreed that cold water immersion after a difficult training or match play made them feel more “refreshed”, less sore and less fatigued. Despite the discomfort of sitting in a cold-tub for 10min, all were more than willing to do it.

As far as a recommendation on cold water immersion, most studies show positive effects on performance, muscle damage and the perception of pain and fatigue and this study confirms that players “feel better” using the cold bath. Since players tend to perform better when they feel better, their perception might lead to improved performance during the match. Thus, trainers can confidently recommend this type of treatment for post-match or post-training recovery.

Reference:

Roswell GJ, Coutts AJ, Reaburn P, Hill-Hass S (2009) Effects of cold-water immersion on physical performance between successive matches inhigh-performance junior male soccer players. Journal of Sports Sciences. iFirst article.

Other Studies:

Halson SL, Quod MJ, Martin DT, Gardner AS, Ebert TR, Laursen PB. (2008) Physiological responses to cold water immersion following cycling in the heat. International Journal of Sports Physiology and Performance, 3: 331-346.

Bailey DM, Erith SJ, Griffin PJ, Dowson A, Brewer DS, Gant N, Williams C (2007) Influence of cold-water immersion on indices of muscle damage following prolonged intermittent shuttle running. Journal of Sports Sciences, 25:1163-1170.
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Cutting-Edge Research: Soccer is a Very Safe Youth Sport

With the rise in popularity of youth soccer, concerns have been raised regarding safety. Studies have suggested that elite soccer is associated with a high incidence and severity of injury. On the other hand, as discussed on the Science of Soccer Online, soccer is an ideal activity for young children to develop fitness and coordination. But, is there a risk of injury for these kids? Unfortunately most of the studies looking at injury rates in soccer have focused on adults and elite players and there is very little information about injuries in young children. A new study published by the American Journal of Sports Medicine finds that the risk of injury for players 6-16 years old may be much lower and argues that soccer is a very safe sport for children.

Researchers from the Oslo Sports Trauma Research Center analyzed injury reports from local soccer clubs. They focused on children 6 to 16 years of age playing organized 5- and 7-a-side soccer. A total of 121 teams and 1879 players were followed over the course of a season. Research physical therapists were assigned to the teams to record, monitor and evaluate all injuries.

The researchers found that the injury rate was very low. For players 6-12 years old, the rate was less than 2 injuries per 1000 hours of play. For older players, 13-16 years old, the rate was slightly higher but still very low. Most of the injuries were considered mild and there were very few injuries that required players to miss more than three weeks of play. Injuries usually involved contact with another player. Ankle and thigh injuries were the most often injured body part. Give the amount of play, team size and injury rate, coaches could anticipate about 1 mild injury per team per season.

Based on this information, the researchers conclude that soccer is a very safe sport for children. Children playing small sided games experience few injuries and rarely experience a serious injury. It seems that soccer is an ideal sport for young children. Soccer programs can enhance both fitness and motor skill development of children. We now know that that can be accomplished at very little risk of injury.

Reference:

Froholdt A, Olsen OE, Bahr R (2009) Low risk of injuries among children playing organized soccer. American Journal of Sports Medicine, in press (doi: 10.1177/0363546508330132)
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Cutting-Edge Research: Chocolate Milk for Tournaments?

After an intense match, muscle glycogen and blood glucose levels may be very low. That is, athletes may be very low on energy. The only way to refuel the system, so to speak, is through the diet or post-game meal. During a tournament, when two matches are played on the same day, players need to have a nutritional strategy to prepare themselves for the second match of the day - what to eat and drink between matches. In a study just released by the journal Applied Physiology, Nutrition and Metabolism, investigators from Northumbria University found that chocolate milk might be an ideal recovery drink.

The study examined the effects of three drinks on recovery and performance, chocolate milk (2%), Gatorade and Endurox. The subjects first exercised on a stationary bicycle for ~65 minutes, alternating 2 min intervals of pedaling at 75% and 50% of their max. This bout of exercise was designed to deplete the muscles of glycogen. They were allowed to recovery for four hours after which they rode at 70% of their max for as long as possible. During the recovery they drank one of the three beverages. Part was consumed immediately after exercise and the rest 2 hours later (~500ml or 1 pint total).

The investigators found that when the subjects drink chocolate milk during the 4 hour recovery period, they able to exercise longer considerably during the endurance trial (32 min versus 23 and 21 min). The difference was remarkable with chocolate milk resulting in increased endurance of 43-51%.

Compared to most sports drinks, 2% chocolate milk has slightly more carbohydrate and much more fat and protein. The benefit of chocolate milk may lie in these latter ingredients. Studies have shown that consuming a small amount of protein with carbohydrate during recovery enhances the muscles replenishment of glycogen. Also, a small amount of fat can raise blood levels of free fatty acids which can be used as energy during prolonged exercise.

There are a few problems with the study that might account for a portion of the difference in performance between the endurance trials. Also, the amount of beverage consumed, ~16 oz over a four hour period is probably less than the typical athlete might drink between matches. However, despite those concerns, the study has important implications for soccer, especially at tournament time. The initial exercise bout and the recovery time are similar to what takes place at many tournaments. Despite some of the soccer governing bodies wanting to limit teams to one match per day, most tournaments still require teams to play two matches per day. Usually these matches are separated by 3-4 hours. Thus, the time course of the study simulates tournament conditions, Also, the initial bout of exercise with alternating periods of high and moderate intensity exercise is similar to what is performed during a match.

On balance this study agrees with an earlier post on the Science of Soccer Online. Milk, particularly chocolate milk, seems to be a very effective recovery drink.

Reference:

Thomas K, Morris P, Stevenson E (2009) Improved endurance capacity following chocolate milk consumption compared with 2 commercially available sports drinks. Applied Physiology Nutrition and Metabolism, 34: 78-82.
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Cutting-Edge Research: Psychological and Emotional State Following a Concussion

Unfortunately, head injuries are all too common in sports. Concussions occur in a variety of sports including soccer. Typically head-to-head or head-to-ground contact can result in injury ranging from a mild to severe concussion. These injuries should be taken seriously and the return to play taken slowly. A new study from a group of Canadian researchers indicates that the psychological and emotional response to head injury is much different from the responses to other types of injuries. The sluggishness and lack of energy that follows a concussion need to be taken into account when injured athletes return to play.

The study appears in the January 2009 issue of Clinical Journal of Sports Medicine. It examined the mood state of three groups of athletes – those who had suffered a concussion, a musculoskeletal injury (sprains, fractures, etc) or no injury. Psychological and mood state analyses were performed over a two week period immediately after being injured. Players were given interviews to determined factors such as mental/emotional fatigue, vigor/energy, confusion, depression and anger.

The researchers found that after injury, athletes who suffered a concussion experienced a high degree of mental and emotional fatigue and a sizeable lack of vigor. These feelings of lethargy were greater than those experienced by athletes who had suffered a non-head injury and those who were not injured. They also persisted for at least two weeks after suffering the concussion. Interestingly, both groups of injured athletes experienced very mild depression after injury.

Following a concussion, there are a number of chemical and metabolic changes within the brain as it attempts to recover from injury. This often results in outward symptoms such as headache, nausea and lack of attention. The lethargy experienced by the concussed athletes is probably another, less obvious symptom of the injured brain.

The key finding of this study is that athletes suffering a concussion may experience lethargy, fatigue and suffer a lack of energy for several weeks after being injured. In some cases, athletes who received a concussion can be cleared from play after 7-10 days. Coaches should realize that even though they are cleared to play, these athletes may appear to be giving less that full effort. They should remember that this is a consequence of a neurolophysiological injury, one in which brain chemistry and metabolism may be altered from some time. Just a limping is an outward sign that an ankle injury is not fully healed, lethargy can be an indication that the athlete is still recovering from a concussion.

Reference:

Hutchison M, Mainwaring L, Comper P, Richards DW, Bisschop SM (2009) Differential emotional responses of varsity athletes to concussion and musculoskeletal injuries. Clinical Journal of Sports Medicine, 19: 13-19.
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Cutting-Edge Research: Sprint and Coordination Training in Preadolescent Players

During the pre-teen years, players undergo marked changes as their neuromuscular system develops. This is a time where tremendous gains are made in stature, strength, coordination and skill. However, the neuromuscular adaptations of young athletes are considerably different than older players. Thus, young players may require more specific training to improve performance. A study by researchers at the Universita degli Studi di Verona indicates that a program of coordination training is as effective as sprint training at increasing sprint speed. However, the coordination training program is far superior at improving sprinting with the ball.

The study which appears in the International Journal of Sports Physiology and Performance enrolled 18 youth players. All were members of the youth program at the AC Chievo Verona professional club in Italy (mean age was 11 years). The players were divided into two groups, a sprint training group (ST) and a coordination training group (CT). Twice each week for 12 weeks the ST group performed a series of 10, 10m and 20m maximal effort sprints. Each sprint was separated by a full recovery (60-90sec). The CT group performed a series of coordination drills that included speed ladder runs, high-knee skipping, lateral skipping and change of pace runs. After the 30min training sessions, they all participated in their regular soccer training session.

After training, both groups increased their sprint speed by ~2.3% and neither group improved their vertical jump height. However, the ST group failed to improve at sprinting with the ball. On the other hand, the CT group improved sprinting speed with the ball by 5.4%.

These results suggest that a program of coordination training that involves multiple types of rapid movements results in greater improvements of the neuromuscular system than a one-dimensional activity (e.g sprinting). The bottom line is that coordination training may improve motor skills in a way that also improves soccer specific speed such as running with the ball.

Coaches working with pre-teen players should consider coordination training as a part of their training routine. Not only might it improve soccer skill, but studies show that coordination training is an integral part of injury prevention programs. Thus, activities involving speed ladders, skipping and changes in direction may have a double benefit, improving performance and lowering the risk of injury.

Reference:

Venturelli M, Bishop D, Pettene L (2008) Sprint training in preadolescent soccer players. International Journal of Sports Physiology and Performance, 3:558-552.
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Cutting-Edge Research: Compression Shorts and Muscular Performance

Some manufacturers of compression shorts claim that their garments improve muscle circulation, enhance performance and reduce post-exercise muscle soreness. Indeed, many athletes feel that compression shorts are a necessity. Are these claims true? What does research say about the use of compression shorts? A recent study to be published in the Journal of Science and Medicine in Sport suggests that the effects of compression shorts on performance and recovery from exercise are minimal. However, a review of several research studies does hint at some potential benefit.

The study, conducted at Charles Stuart University in Australia, focused on sprint and plyometric performance and exercise recovery. A group of trained athletes performed a series of 10 repeated sprints and a series of 10 repeated bounds while wearing typical gym shorts and compression shorts. During these trials, there was no difference in sprint times or bounding distances between the two conditions. This despite that fatigue was apparent in both types of exercise. In the days following the exercise tests, the investigators found no differences in biomarkers of muscle soreness. Nor did they find any differences in electrically stimulated or involuntary muscle force (this is important as it diminishes any potential of a placebo effect – see below). These results lead the investigators to conclude that the use of compression garments probably does little to reduce fatigue or enhance the recovery of performance in the days following exercise.

A review of the scientific studies on the effects of compression garments on muscle performance shows that research results are very inconsistent. Most of the studies fail to find any improvement in speed or power but a few studies show small improvements. The studies which demonstrate positive effects on performance typically report very small improvements which may be due to factors other than the shorts. No study has shown any adverse effect. Based on the results of 4-5 well conducted studies studies, it is questionable as to whether or not compression shorts enhance performance.

These research studies do lead to two fairly firm conclusions. First, there seems to be a rather strong placebo effect of wearing the shorts. Nearly all of the studies report that the athletes felt they performed better and experienced less muscle soreness after wearing the shorts. Thus, the athletes perceive that compression shorts are beneficial. Unfortunately the unbiased physiological measurements do not support the athletes’ perceptions.

Second, the shorts do seem to reduce hip flexion during running and jumping and increase skin temperature. This raises the possibility that compression shorts might provide some protection against hamstring injuries. The emphasis here is “possibility” and “might”. None of the studies provided any data to support a firm claim of injury protection and more research is needed to address this question. Nevertheless, there is the possibility that compression shorts might aid in reducing the risk of hamstring injuries.

Based on the published research, it is clear that compression shorts do not hinder exercise performance and may offer some protection against hamstring injuries (although this protection may be minimal). However, they are not likely to offer any improvement in performance nor are the likely to reduce the development of muscle soreness (although athletes may perceive benefits). Therefore, there is no reason to discourage athletes from wearing compression shorts during training or matches but they should not expect to receive any measurable benefit on performance.

Reference:

Duffield R, Cannon J, King M (2009) the effects of compression garments on recovery of muscle performance following high-intensity spring and plyometric exercise. J Sci Med Sport, doi: 10:1016/j.jsams.2008.10.006.
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Cutting-Edge Research: Offsetting Fatigues Effects on Passing Accuracy

American football coaches often use the quote, “fatigue makes cowards of us all”. Fatigue can also have other negative effects on performance. An earlier post described what happens to passing accuracy as fatigue develops. Using the Loughborough Soccer Passing Test (LSPT), researchers showed that fatigue, whether caused by match-play or high-intensity running markedly reduced the accuracy of short passes. In a new study appearing in the journal Applied Physiology, Nutrition and Metabolism, researchers found that a four week program of interval training lessened the effects of fatigue on passing accuracy. They suggest that aerobic training might benefit players in terms of maintaining their technical skills at the end of a match.

Dr. Franco Impellizzeri and colleagues divided the 18 year old trained soccer players into two groups. One group served as a control group while the other participated in four weeks of an interval training program. For the LSPT, players were asked to complete 16 passes to different targets as fast as possible. Penalty time is assessed when the passes do not strike the target (see the earlier post for a detailed description of the LSPT). Players performed the LSPT before and after a bout of fatiguing exercise and repeated the testing before and after the four-week training period.

Prior to starting the training program, both groups LSPT performance declined as the result of fatigue. Both the total time needed to complete the test and the assessed penalty time was increased. This is consistent with what had been found previously – fatigue negatively impacts passing accuracy.

At the end of the four weeks, the training group had improved VO2max (aerobic fitness) and performed better on the Yo-Yo Intermittent Recovery Test. As expected, interval training increased fitness. More importantly, the increase in penalty time caused by fatigue was reduced following training. In the fatigued state, the trained players were able to accurately complete more passes than was the control group. In short, they suffered less deterioration of their technical skills.

The important outcome of this study is that aerobic training (in this case interval training) seems to offset the effects of fatigue on technical performance. It’s not clear if this results from improved muscle fitness or some neuro-cognative improvement. Whatever the explanation, this study emphasizes that aerobic training might improve the player’s ability to accurately execute short passes during the later stages of a match. This is yet another important reason to include a fitness component in the player’s regulalr training routine.

Reference:

Impellizzeri FM, Rampinini E, Maffiuletti NA, Castagna C, Bizzini M, Wisloff U (2008) Effects of aerobic training on the exercise-induced decline in short passing ability in junior soccer players. Applied Physiology, Nutrition and Metabolism, 33:1192-1198.
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Cutting Edge Research: A Modified Version of the FIFA 11 Reduces Injury Rate In Young Women.

The FIFA 11 training program focuses on core stability, balance, and neuromuscular control as part of a warm-up routine. The goal is to lower the risk of knee and ankle injury in female players. A previous post on the Science of Soccer Online reviewed two studies suggesting that the “FIFA 11” injury prevention program may not be as effective as advertised. The authors of these studies felt that the program’s effectiveness may be limited by the lack of progression (increasing intensity as players improved fitness). A new study used a modified version of the program that was more intense and includes different levels of progression. The researchers found that total injuries, overuse injuries and severe injuries were all reduced in teams using the program. The researcher also found that a key component of the effectiveness was compliance. Those teams with higher compliance, experienced lower injury rates. These findings are very encouraging – including a 20 minute training routine as part of the daily warm-up may markedly reduce the risk of injury in young, female athletes.

The study enrolled clubs in the 15-16 year old division of the Norwegian Football Association. These clubs trained 2-5 times per week and played 15-30 matches over the course of the eight month season. 52 clubs (1055 players) were placed in the intervention group where they utilized a modified version of the FIFA 11 training program. These clubs were asked to use the program at least twice per week as a part of their normal warm-up routine. 41 clubs (837 players) were placed in the control group where they followed their regular training routine.

A description of the program is shown in the figure (taken directly from the research report). An excellent description of the program along with instructional videos can be found using the links below. The focus is on development of strength, balance, core stability and technique. In particular, the athletes were instructed to emphasize hip control and knee alignment and to avoid excessive knee valgus when landing (a knock-kneed position). Once the players were familiar with the program, it took ~20 minutes to complete. The primary difference between this program and the original FIFA 11 is that it allows for progression of intensity. As the players developed strength and balance, they progressed through three different levels.

During the course of the season, all injuries were recorded. Medical personnel noted the site and type of injury as well as the severity.

Over the course of the eight month season, the researchers found that there were lower risks of overall injuries, overuse injuries and severe injuries (those requiring >25 days or recover) in the intervention group. The rate of acute injury to the lower extremity was reduced by 52% in this group. In particular the incidence on knee injuries was reduced by 46%. Interestingly, the incidence of chronic injuries such as tendon pain and low back pain were reduced by more than 60%.

Based on these results, the authors concluded that the “risk of injury can be reduced by about one-third and the risk of severe injury by as much a half” using the modified version of the FIFA 11 as a part of a comprehensive warm-up program.

The authors found that compliance was a key to the programs effectiveness. Those clubs that adhered to the program and utilized it as prescribed (at least twice per week), experienced the lowest injury risk. The reduction in injury incidence was somewhat lower in clubs with lower compliance.

Research shows that neuromuscular training that focuses on core stability, balance and neuromuscular control and emphasizes hip control and knee alignment (avoiding the valgus position) can reduce the risk of knee and ankle injury in female soccer players. This study shows that a relatively short program (~20 minutes) used a part of the regular warm-up routine can also lower injury risk. As for application by coaches, most teams spend 15-20 minutes warming up for the day’s training session. Thus, the program would not cut into the practice time devoted to technical and tactical training. Simply using a more focused approach to the warm-up and including strength, balance and plyometric training, teams may be able to lower the risk of injuries. Given the increased risk of knee injury in female players, any program that can be conveniently employed AND may cut the injury risk by 1/3-1/2 should be strongly considered.

Reference:

Soligard T, Myklebust G, Steffen K, Silvers H, Bizzini M, Junge A, Dvorak J, Bahr R, Andersen TE (2008) Compehensive warm-up programme to prevent injuries in young female footballers: cluster randomized controlled trial. British Medical Journal, 337:a2469 (doi:10.1136/bmj.a2469).

Additional Links:

Oslo Sports Trauma Research Center (program description and materials).

Instructional Videos (in Norwegian)

Footnote:

A word of thanks to Iain Milligan for bring this article to my attention.
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