Thursday, March 6, 2014 Balance, Fatigue and Carbohydrates

Over the past few years, coaches and researchers have been asking how balance affects different athletes. For sports such as gymnastics, the need for balance is obvious. In other sports like soccer, research shows that the ability to maintain balance also influences performance during cutting and changing directions. We also know that balance plays an important role in injury risk. Balance results as a response to various sensory inputs – both visual and mechanical. The central nervous system (CNS) processes this information then activates the appropriate muscles to reposition the body and/or to stabilize a joint. When the CNS cannot respond appropriately, players may fall or they may sprain or tear ligaments. Thus, a loss of balance is a key to players playing well and staying healthy. Two recent studies examined the relationship between fatigue and balance in young athletes. The first shows the extent to which fatigue disrupts balance while the second suggests that carbohydrates may be a solution to maintaining balance during a match.

In the first study, the researchers asked the question, how much does fatigue affects balance in young soccer players? Earlier studies looked at older, adult players but this is the first to focus on youth. The players were 14-15 year olds selected from competitive teams. Balance was measured by having the players stand on a pressure platform using one and two-legged stances. The pressure platform then measured “postural sway” – the degree and speed in which the athlete’s center of gravity swayed forward, backward, left and right. The greater the sway, the less balance exhibited by the player. The players did this before and after undergoing intense exercise designed to induce fatigue. For the fatigue protocol, the players were asked to go through several minutes of a moderate-intensity warm-up, and then perform six, 2 x 15 meter shuttle runs, separated by 20 seconds.

After exercise, the players’ balance was markedly disrupted. Regardless of which leg they stood on, their body swayed much more after fatigue than before. This was true for the amount of sway and how quickly they swayed to the front, back and side. In fact, the loss of balance was directly related to the degree of fatigue experienced – greater fatigue, more sway and less balance.

Similar to older, adult players, fatigue greatly affects balance in young soccer players. The authors point out that 14-15 year olds are still developing their proprioception and balance control systems. In these players, “neuromuscular immaturity”, weakness, fitness and training may also influence fatigue’s ability to disrupt balance. They go on to emphasize the role training plays in developing balance and avoiding injury in this age group.

The second study looked at young gymnasts (11-14 years old) and balance beam performance. The objective here was to determine how fatigue and a carbohydrate supplement affected the number of falls. One group of athletes underwent a warm-up followed by five sets of beam exercises. A second group participated in the warm-up plus 20 minutes of intense gymnastics training (designed to induce fatigue) before performing the five-set beam exercise. Shortly the beam routines, both groups of gymnasts were given either flavored water or a carbohydrate beverage.

As in the soccer study, fatigue affected balance by increasing the number of balance beam falls from 3.3 to 5.4 (63%). Interestingly, the carbohydrate supplement reduced falls regardless of the athlete’s level of fatigue. After intense exercise, falls were reduced to an average of 2.3. Without exercise, they were reduced to 1.9. Thus, a carbohydrate beverage can improve balance and balance beam performance in both fatigued and non-fatigued gymnasts.

What is interesting about this study is that the gymnasts did not experience a decline in blood glucose (hypoglycemia) following the intense training bout. Hypoglycemia often accompanies fatigue and can have negative effects on performance where effort, motivation or motor skill is involved. In fact, we often attribute the positive effects of carbohydrates on either prevention or reversal of hypoglycemia. In this study, hypoglycemia did not occur. Nevertheless, the researchers attributed the reduction in falls with carbohydrates to improved focus and attention.

Previously on the SSO, we’ve discussed an interesting effect of carbohydrates on athletic performance. As it turns out, players may not need to actually ingest carbohydrate drinks to gain an advantage. A “rinse and spit” method can also improve performance. That is, swishing the beverage in mouth without actually ingesting it has a psychological effect on performance by improving effort and skill. It seems that there is a link between the mouth and the brain that is somehow stimulated by carbohydrates. In fact, brain imaging studies show that just the presence of carbohydrates in the mouth activates regions of the brain involved in reward and the regulation of motor activity. This may be what affected the gymnasts’ performances. Carbohydrates in the mouth stimulated the brain and improved focus, attention and/or motor skill leading to improved balance and fewer falls.

Back to the soccer players and their balance problems with fatigue. The authors of the first study point out that neuromuscular training programs that include balance, strengthening and plyometric exercises are the best option to increase balance and reduce injury risk (as well as improve performance). This is especially true in young athletes. However, if carbohydrate beverages can improve balance and reduce falls in fatigued gymnasts, one can assume that they would do the same in fatigued soccer players. Thus, carbohydrate drinks given before and during training or matches, may be an additional tool for preventing injuries. By affecting the brain, carbohydrates may restore balance, prevent unwanted joint movements and reduce the risk of sprains, ligament tears and falls.

We’ve known for years that carbohydrate beverages provide fuel and hydration, both of which affect performance. This added benefit, linking the mouth to the central nervous system may aid in maintaining balance. To be truthful, this idea hasn’t been studied in detail. However, it is food (or drink) for thought.

References

Massimilano P, Ibba G, Attene G (2014) Fatigue-induced balance impairment in young soccer players. Journal of Athletic Training, in press, doi: http://dx.doi.org/10.4085/1062-6050-49.2.12

Batatinha HAP, et al. (2013) Carbohydrate use and reduction in number of balance beam falls: implications for mental and physical fatigue. Journal of the International Society of Sports Nutrition, 10:32.

Chambers ES, Bridge MW, Jones DA (2009) Carbohydrate sensing in the human mouth: effects of exercise performance and brain activity. Journal of Physiology, 587: 1779-1994.
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Labels: Current Research, Injuries, Nutrition

Match Analysis and the Recovery Process

Match analysis has become an important tool in assessing team performance. Knowing team and opponent tendencies, individual player performance indicators, and markers of fatigue can help the coach or manager formulate match strategies and pinpoint team and individual weaknesses. Thus, it is not surprising that sport scientists are very interested in how match analysis can be used to improve their team and move them up the league table. In a new study, researchers at the Université Lille Nord de France and Lille Métropole Football Club took a different look at match analysis. They compared match analysis data to various performance indicators measured during three days of recovery. They found several interesting relationships between various player movements and prolonged decrements in physical performance. Their results have important implications for understanding the recovery process as well as preventing potential injury.

Match analysis was performed during four competitive matches to establish various playing actions completed by the players. At 1, 2 and 3 days following the matches, the players provided subjective ratings of fatigue and muscle soreness. They also underwent several physical tests of strength, sprint, and power performance. Data obtained at each recovery interval were compared to baseline measurements taken earlier in the season. During the post-match recovery period, players continued their regular training routine but were asked to avoid recovery treatments such as ice baths, compression garments and massages.

During the three-days after the match the players reported several perceptions. They felt a greater sense of fatigue at the 24-hour mark that subsided by 48 and 72 hours. They also reported increased muscle soreness across all three post-match days. This sensation of muscle pain and discomfort was associated with increased blood creatine kinase levels, a key indicator of muscle damage.

In terms of physical performance, power output was decreased by 5-6% over the course of the recovery period. Both peak sprint speed and vertical jump measures were depressed for up to 72 hours post-match. Also, hamstring strength in both the dominant and non-dominant legs were reduced for the duration of recovery. The researchers found between 6 and 8% reductions in dynamic strength of these muscles.

Match analyses showed that the changes in muscle soreness were most closely linked to the number of short sprints performed during the match. Fatigue and physical performance were linked to the number of hard directional changes and the number of tackles executed. This is not surprising. Sprinting and changing directions requires rapid acceleration and deceleration. Both of these actions require forceful concentric and eccentric muscle contractions. We’ve known for years that eccentric or lengthening contractions leads to both fatigue and delayed onset muscle soreness. However, this is the first study to link movement patterns and player actions during a match to the degree of soreness and physical performance decrements.

The finding that hamstring strength was depressed for up to 72 hours post-match has important implications for the recovery process as well as the risk of anterior cruciate ligament injury. As we’ve discussed previously on the SSO, ACL injuries is a growing problem. Recognizing, understanding and correcting risk factors can go a long way in preventing injuries. We’ve known for years that both weak hamstrings and muscle fatigue increase injury risk. When various movements stress the ACL, the hamstrings contract to help stabilize the knee. With fatigued or weakened hamstrings, this aspect of stability is reduced and the potential for sustaining and injury increases.

This study shows that hamstring muscle fatigue may persist for up to 72 hours after a match. Many college, high school and youth club schedules require multiple matches to be played with as little as 24 hours of recovery. The Atlantic Coast Conference has adopted a Thursday and Sunday schedule of women’s matches, leaving 72 hours of recovery from the first match to the second. Other teams and conferences used a more congested format, a Friday and Sunday schedule. Based on the current research article, it is quite possible that many players are not fully recovered by the start of the second match. That is, hamstring strength may remain depressed, raising the risk of ACL injury. This may be particularly true if the preceding match required players to execute an abnormally high number of short sprints and changes in direction.

Unfortunately, there is little information on injuries occurring during this schedule of matches. And, to be truthful, we don’t know if more injuries occur during the 72 hours after a difficult match. Despite this, coaches should take caution and consider this information when faced with a congested calendar. At the very least, coaches should be aware that player performance may suffer for up to 72 hours after a difficult match. Strategic use of player substitutions could reduce the number of key player movements (sprints, direction changes) and may be able limit fatigue in the initial match. Targeted exercise recovery regimes may also speed the recovery process between matches. In this study, players were not allowed to use treatments such as ice baths, compression garments or massage. While the research is not completely clear on how well these techniques actually aid the recovery of muscle force, some argue that they may offer some benefit. Finally, research is clear that a proper nutritional recovery strategy can enhance the recovery process. High carbohydrate foods and beverages containing some protein taken immediately after the match are critically important to recovery. Continuing the process with nigh carbohydrates meals and plenty of fluids is important as well.

Understanding how the physical demands of the match can impact subsequent performance is important over the course of a season. And, recognizing how a strategic recovery process can affect both performance and injury risk can go a long way in the team having a successful season.

Reference

Nedelec M, McCall A, Carling C, Legall F, Berthoin S, Dupont G (2013) The influence of soccer playing actions on the recovery kinetics after a soccer match, Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000293.

Can Strength Training Improve Kick Velocity or Distance?

Playing a quality long ball is an important piece of the soccer performance puzzle. Goalkeepers, defenders and midfielders routinely take free kicks and play direct balls where considerable distance on the kick is needed. Add to that, the need for attackers to strike high-speed shots and it is easy to see that kicking velocity and distance are critical to success. However, can this aspect of a player’s game be improved? Is it possible for a player to increase his or her kick distance through training? Leg strength and power are known to be important for many soccer skills such as sprinting, stopping, cutting and jumping. Can strength training, which improves leg strength and power, also benefit a player’s kick? Researchers at the University of Nevada Las Vegas found that players are able to improve kicking distance through a simple, low-intensity plyometric training program. They found that young girls, who engage in such a training program, can improve their kicking distance by more than 25%.

The players used in the study were 13-14 year old members of two local club teams. They all had a minimum of four years of competitive playing experience and the two teams were similar in terms of ability, experience and training. One team participated in regular soccer practices while the other also participated in a once-weekly plyometric training program.

The plyometric program was fairly low intensity. During weeks 1-6, training involved single- and double-leg hops over six- and ten-inch hurdles, lateral hops and shuffles over ten-inch hurdles and a 12-inch box. During weeks 8-14, training included 10-inch box and depth jumps and cutting drills.

All of the players were tested on their kicking distance and vertical jumping ability before the start of training and at weeks 7 and 14. For the kicking distance tests, a stationary ball was kicked and it was required to land within an 8-yard wide target lane. Distance was measured from the point where the ball was kicked to the first landing point.

The researchers found that kicking distance steadily improved in the polymeric training group. At 7 weeks, distance increased by 10% and at 14 weeks, it improved by more than 27%. In the group that did not undergo plyometric training, their kicking distance actually decreased over the course of the study.

Plyometric training also improved vertical jumping ability. In the trained group, vertical jump increased by 8% and 19% at 7 and 14 weeks. The control group’s vertical jump did not change.

The results of this study show that in teenage girls, a once-weekly program of low-intensity plyometric training can improve both kicking and vertical jumping ability. What is remarkable about this study is that the training program was fairly low-intensity and was performed just once per week. Yet, the gains in power and kick distance were quite impressive. This suggests that using plyometrics and adolescent female players can yield a considerable bang for the training buck.

Researchers at the University of Ballarat in Victoria, Australia reviewed the research on strength training and kicking. They found that a majority of studies report similar results – strength training in general and plyometric training specifically can improve lower body power as well as kicking velocity and distance. The key seems to be improving power of the hip flexors and, to a lesser extent, the knee extensors (quadriceps muscles).

Those studies that failed to find improvement in the player’s kick generally used elite players as subjects. At the elite level, it may be more difficult to achieve large improvements in performance with strength training. That is, they perform at such a high level that there may be very little room for improvement, especially over the course of a 12 to 14 week study. However, for the younger, less experience players, strength training does seem to be effective.

A word of caution about strength training focused on improving the kick. While knee extensors strength is important, focusing on developing the quadriceps muscles without increasing strength of the hamstrings (knee flexors) can raise the risk of knee injury. A key risk factor for anterior cruciate ligament injury is an imbalance of quadriceps and hamstring strength. Thus, during training, it is VERY important to train BOTH the quadriceps and hamstring muscle groups.

It is also important to point out that these studies focused on kick velocity and distance. They did not address accuracy. However, the Australian researchers note that there is a trade-off between velocity and accuracy. In general, as kick velocity increases, accuracy decreases. They argue that there is some sub-maximal kick velocity at which accuracy can be maintained. After which accuracy deteriorates. If strength training increases a player’s maximal kick velocity, it should also increase this sub-maximal velocity. Thus, training should increase the speed of the players most accurate shot. More research is needed, however to fully verify that idea.

The bottom line, when working with young players, a strength training program that includes plyometrics can benefit performance. Not only can it improve shot velocity, it can also improve other measures of soccer performance and reduce the risk of injury.

References:

Rubley MD, Haase AC, Holcomb WR, Girouard TJ, Tandy RD (2011) The effect of plyometric training on power and kicking distance in female adolescent soccer players. Journal of Strength and Conditioning Research, 25: 129-134.

Young WB, Rath DA (2011) Enhancing foot velocity in football kicking: the role of strength training. Journal of Strength and Conditioning Research, 25: 561-566.

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Labels: Current Research, Training
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