Sports Medicine for Youth Soccer

Training for Optimal Performance

Soccer is a major sport for young athletes in the United States, and is also rapidly becoming a major sport for males and females for all ages. Because young athletes go through puberty at different times, they vary a great deal among each other in size and maturity. These differences pose a challenge to the athletes and their coaches. The primary characteristics of a young athlete are: motivation; physical fitness (i.e. muscle strength, power, endurance, flexibility, proper body composition, and cardiac respiratory endurance); discipline, coachability; skills; ability to be a part of a team; ability to think under stress; and good spatial orientation.

The practice sessions for soccer should seek to achieve: physical conditioning, repetitive training, proper intensity of training, flexibility, and awareness that the achievement of proper endurance for the soccer athlete requires 4-6 months of training. Also, the coach should be aware that extreme and severe high intensity and high frequency training causes damage to muscle tissues and is counterproductive to the goals of the athlete. The pre-game meals should primarily be composed of carbohydrates, and balanced meals should be eaten prior to game days. Water consumption (hydration and rehydration) should be strongly encouraged with water breaks built into the training schedule and water available upon demand.(2)

Physiological and Chronological Age

Any middle school teacher can tell you that adolescent teenagers are difficult to handle and that they vary a great deal in size, height and maturity. This is because teenagers, in addition to possessing the normal genetic inheritance of size from their parents, are also in a very fast growth period (puberty). The growth spurt on the average is around 12 years of age for girls and 14 years of age for boys. Young athletes are experiencing a turmoil period which affects them both physiologically and hormonally. Therefore, young athletes come to soccer with these inherent and at times large differences in size, shape, height, and skill level. Because of these differences, it is very difficult to mold a team at this age group into a skilled unit.

Characteristics of a Soccer Player

All of the following player characteristics need not be present before the individual plays soccer. However, the individual should either show aptitude or at least a willingness to acquire these characteristics.

 

1. Motivation

The soccer player should be interested and motivated to play the game of soccer (i.e. kicking a ball, running, passing a ball, etc.). In other words, the player is receiving an enjoyment out of performing these tasks especially when it is performed spontaneously and without adults forcing them to do so.

2. Physical Fitness

The term physical fitness connotes different meaning for different activities. In the

context of soccer, it is the ability to play soccer for 60-90 minutes without fatigue, exhaustion, or other malsymptoms of a sedentary person. The player should have the following physical fitness characteristics to play soccer:

a. muscle strength and power
b. endurance
c. flexibility
d. proper body composition
e. cardiac respiratory endurance

3. Discipline

The ability to practice and play the game in a repeated fashion several times a week.

4. Coachability

The ability to take instructions and to try to comply with these instructions.

5. Skills or ability to learn skills

The ability to conduct or learn individual soccer skills with the ball such as kicking, receiving, passing, shooting, control, etc.

6. Ability to play in a team sport

The ability to cooperate with other team members to achieve a difficult task. Also, the player should have the ability to accept less personal recognition for the sake of the team. The player also should be able to associate with others for a long time and sometimes under stressful conditions. Finally, the player should have the ability to enjoy himself with others.

7. Ability to think under stress

Most people are not as logical under stressful conditions as they are normally. However, the well trained soccer player learns what to do under the various game conditions, and also learns to think quickly under stressful conditions.

8. Good Spatial Orientation

The ability to think and visualize in three dimensions and to be relevant to the soccer field is difficult for very young players. The player should be able to learn to adapt to the spatial orientation within the field and re-position himself/herself relevant to the ball, teammates and the opposing team members.

 

Practice Sessions

The purpose of this article is not to suggest specific exercises. There are other sources for the numerous soccer practice sessions. However, we will give a general outline that all soccer practice sessions should fall within. In this manner, each coach can use their creativity to make soccer practices more enjoyable and more beneficial to the different needs of the varied groups.

The practice sessions should be designed to make the individual a better soccer player. The best practice for any sport is to play that sport repeatedly in order to develop those muscles, skills, endurance, etc….., for that sport. It is a common occurrence for those who play one sport and then suddenly play another sport to have muscle aches after the first few times of the new sport. This is because they have used a different new set of muscles than they used before. This is called specificity of training. So, the more the soccer player plays soccer, the better he/she will become. This is not to say that the soccer game should not be broken down to small segments so that it can be taught and repeatedly reinforced.

In order to prepare the individual to play soccer, players and coaches should observe the following factors:

 

1. Physical conditioning

Increased ability to sustain both aerobic and anaerobic exercises.

2. Frequency of training

This should be 2-3 times a week for youngsters and 3-4 times a week for adults.

3. Warm-up

Static stretching should last 10-30 seconds and be repeated 3-5 times. Each stretching exercise should include a larger range of motion than the previous one. In addition, after each rigorous practice session, there should be 10 minutes of low to moderate cool-down exercises. Examples of cool-down exercises in soccer are individual skill exercises; jogging lightly, and best of all just walking or dribbling the ball lightly.

4. Time to peak endurance

Quick and severe training for 2-3 weeks prior to a season as is the case in some high schools after sedentary summer, cannot achieve endurance and may be detrimental to the athlete. This is because adaptation of the cardiorespiratory system and muscle enzymes require about six months of training to reach peak endurance capacity. Moreover, it takes 2-4 weeks without training (as may be the case during the summer for high schoolers) to lose most of endurance parameters (see section on endurance for details). Therefore, a well-planned long training period is an essential part of preparing players for the season.

5. Muscle Strength and Power

The use of moderate weight lifting for young athletes to increase strength and power in moderation is an acceptable form of exercise. Weight bearing exercises for children below 13 years of age is not recommended in the standing position where there is a great deal of compression force on the legs. In order to increase muscle strength, the muscle should be challenged by at least 60% of the maximal weight lifted the first time. Furthermore, in subsequent days and weeks, the muscle must be challenged by increasing weights, with high frequency repetition. Remember, an increase in muscle strength is not necessarily associated with a large increase in size of the muscle. Low frequency repetition increases the size of the muscle (body building) rather than increasing the muscle strength. While defenders may be able to use a greater muscle mass and strength, other soccer players need to increase strength more than muscle size in order to keep their agility and speed.

Soccer is a mixture of aerobic and anaerobic sport. Therefore, the training session should combine both modes. Aerobic (like marathon running, jogging, etc…) sessions are usually composed of slow rhythmic exercises. These exercises allow the body to utilize oxygen to burn foodstuff to produce the energy needed. Therefore, the best soccer training sessions should resemble match-like conditions which involve both anaerobic and aerobic exercises. These conditions consist of the player performing, for example, the following tasks:

 

(a) Aerobic exercises such as continuous jogging to re-position to a new ball position lasting 1-5 minutes. Repetition of this action 10-50 times per game.

(b) Anaerobic exercises such as sprinting — lasting from a second to 1 min. Repetition of this action 10-50 times per game.

(c) Midfielders do most of the jogging and sprinting throughout the game since they must perform offensive and defensive tasks.

(d) Defenders tend to do mostly jogging and less sprinting.

(e) Offensive players do more sprinting than jogging.

 

The details of the sessions should be left to the creativity of the coach to combine multiple game-drills that benefit the most for a given player and team.

Usually young players play more than one position (i.e. offensive versus defensive position). However, as the young players pass puberty, they become more specialized in a given general position. Therefore, each position may require slightly different emphasis. For example:

 

(a) Offensive players do mostly sprinting than jogging and therefore would require more anaerobic process adaptation.

(b) Defensive players tend to do mostly jogging and less sprinting and therefore would require more aerobic process adaptation.

(c) Midfielders tend to do both sprinting and jogging throughout the game since they must perform both offensive and defensive tasks. Therefore, midfielders would require an intensive training to adapt to both aerobic and anaerobic processes.(1)

 

Interval Training

The soccer player can benefit from interval training. Interval training consist of work bouts with rest intervals of ratio varying from 1:3 to 1:1 (work/rest) depending on the need and the physical fitness of the individual. The work period can lasts a few seconds up to several minutes. The whole cycle can be repeated 5-20 times. A short high intensity (sprinting) work bout lasting greater than 15 seconds can improve the anaerobic system with rest period of 30 seconds. Interval training to improve the aerobic system could consist of ratio’s of 1:1 or 1:1:5. The exercise period could last 60-90 seconds in order to force oxygen consumption followed with a recovery period varying from 60 seconds up to 135 seconds.(2)

Circuit Training

Circuit training attempts to use economically time of exercise to improve strength, power and cardiorespiratory system. Work sessions should combine resistance, speed and rest. For example, working periods can vary from 30-60 seconds with similar rest periods. The number of different stations could be as high as 15 stations of differing exercises.(2)

Preparations for the Soccer Season

Physical Fitness Assessment

1. Physical Exams and Screening

2. Physical Fitness Tests

 

a. Cardiorespiratory endurance

 

1. Heart rate recovery test
2. Step test
3. Running
4. Walking

 

b. Body Composition

 

1. Anthropometric test
2. Skinfold test

 

c. Muscle Power and Strength

d. Flexibility

 

Prevention of Injuries

 

a. Proper Preparation of teens and players
b. Equal Competition
c. Proper rules and refereeing
d. Proper sequence of warm-ups, stretching, and exercises

 

Protective Gear in Soccer

 

1. Cleats
2. Shin Guards
3. Mouth protector (for persons with orthodontics)
4. Goalies outfit (elbows, knees, and hip cushion)
5. Taping (when necessary)

 

Water and Electrolyte Balance

Water is the most important and critical nutrient to the survival and well being of a person. One can survive without intake of other nutrients for days, weeks, and even months but one cannot survive without water for more than a few days. In a 70 Kg person, the water content is about 40 liters (i.e. 60% of body weight). Most of the water (25 liters) is inside cells of the body and about 15 liters lie outside the cells. The blood volume is about 5 liters and the maintenance of this volume is critical to the survival of the person. For example, daily fluid intake can vary from 1-7 liters, while the blood volume must remain constant. Excess fluid intake can easily be regulated; however, a problem. arises when fluid intake is below one liter per day and blood volume starts to become lower than 5 liters (for example about volume of 4 liters and below can cause death). Under sedentary conditions skin and kidney (i.e. urine output) are the most important regulators of body water. Under the conditions of hot weather and exercises (despite fluid intake in many cases, the skin (sweating) becomes the only important regulator of body water as well as the body temperature. The daily loss of water in a heavy, prolonged exercise (3 hours marathon) can increase from 0.1 to 5 liters.(6)

Sweating is absolutely necessary in order to maintain constant body temperature. The sweat rate usually corresponds to increases in energy expenditure by the athlete. Trained athletes have a more sensitive sweating system than non-athletes due to adaptation by the repetitive exercises. Of the 5 liters of H2O, a marathon runner’s losses (despite fluid intake in many cases) represent 12% of body water and 8% of body weight. Anything above 2% weight loss due to exercise induces severe demands on the thermoregulatory and cardiovascular systems.

All of the energy expenditure during exercise ends up as heat. Therefore, body temperature will rise rapidly during exercise if cooling due to sweating is not functioning. The prolonged increase in body temperature will eventually cause serious damage to the thermoregulatory system, which can result in serious damage to the brain — the most sensitive organ. Thirst, unfortunately, is not a reliable indicator during exercise (i.e. under any stressful conditions). Therefore, athletes should drink water not just to quench their thirst, but as part of their exercise regime. Figures 3 and 4 represent a hypothetical daily water output and water intake for persons who are: sedentary, a marathon running for 3 hours, or soccer players (90-100 minutes). The numbers are rough estimates, and for illustration purpose only. The most scientific way to determine how much water intake ought to be is to weigh the player before and during the game. The loss of weight due to water loss should be adjusted by drinking the same amount of water. Remember, it is better to drink more than less water.

Children utilize a greater metabolic energy and thus produce more heat than adults to perform the same task. Fortunately, children dissipate heat better than adults due to a larger surface area to mass ratio than adults. However, when ambient temperature is hot and humid, the dissipation of heat is inhibited and thus children maybe at a greater risk than adults during exercise.

Electrolytes such as Na+, K+, Cl-, Ca2 and Mg2+ are the most important ions and their amount in the cell and the blood is critical in maintaining normal body function. As we sweat more during exercise, the amount of these ions in the sweat is less than that of the blood. In other words, the body is losing more water than ions. Under heavy exercise conditions, the body loses about 5-7 grams sodium chloride. However, there is a minimal loss of K+ and Mg2+. Under conditions of continued exercise (up to 80-90 minutes) there is a need to replenish water continuously, but not salt. If there is heavy exercise beyond the 80-90 minutes, salt replenishment is appropriate. The use of salt tablets during the early phase of exercise (in most cases of soccer) is detrimental to the body. The body fluid has a higher salt concentration after exercise than before; therefore, the body needs pure water to bring the blood composition back to normal levels.(6)(2)

Heat Related Illnesses

Heat Cramps

They are similar to other muscle cramps, which may be due to: sudden blows; over exercise; lack of blood supply, etc.

 

Cause: Reduced blood flow to the muscle due to: loss of water, prolonged loss of minerals, etc.

Symptoms: Spasmodic tonic contraction of a given muscle.

Onset: Gradual or sudden.

Danger: None if treated. Heat cramps could lead to termination of that particular exercise for a few days.

Prevention: Proper physical fitness, proper warm-ups and stretching exercises prior to the activity and temporary termination of activity.

Treatment: Termination of activity. Stretching, rest and ice treatment necessary.

 

Heat Exhaustion

 

Cause: Loss of water.

Symptoms: Tiredness, weakness, malaise, and progressively weaker.

Onset: Gradual and over several days.

Danger: The player may go into shock because of reduced blood volume This rarely happens, however, as it is not an emergency condition.

Prevention: Proper physical fitness and proper hydration before and during the exercise and termination of activity.

Treatment: Cooling, drink water, and later drinking large amounts of mineral rich fluid such as fruit and vegetable juices.

 

Heat Stroke

Brain cells in the hypothalamus maintain body temperature close to 98.6oF. These cells respond to the blood temperature that passes through them. The cells regulate the skin by sending signals to release skin vasodilator in order to increase sweating. When rectal temperatures reach 41oC – 43oC, unconsciousness may develop; if that happens, the mortality rate ranges from 50-70%. Heat stroke is the second cause of death among athletes.

 

Cause: Loss of water and sudden uncontrolled rise in body temperature due to the failure of the thermoregulatory center in the brain.

Symptoms: It is a Medical Emergency. May lead to death or irreversible damage. Person shows behavioral or mental status changes during heat stress. These symptoms include: sense of impending doom, headache, dizziness, confusion and weakness. Symptoms that could lead to heat stroke are:

 

a. high temperature and high humidity
b. high rectal temperature
c. hot dry skin
d. cardiorespiratory and central nervous system disturbances
e. clouded consciousness and finally collapse

 

Onset: Sudden

Danger: Brain damage and death is imminent if not treated quickly.

Prevention: Proper physical fitness and proper hydration before and during the exercise and termination of activity.

Treatment

 

1. Call for an ambulance.
2. Remove clothes and cool with ice and cold water on the body.
3. Monitor vital signs. (i.e. breathing, heart beat, pupil size).
4. Massage extremities to promote cooling.
5. Once the body temperature cools and the person is quite alert, remove from cold environment to prevent hypothermia.(3)

 

In the hospital they may perform the following:

 

1. Administer I.V. fluid (1400 ml for first hour).
2. Monitor urinary output – Mannitol may be given to promote urination.
3. Digitalis may be considered for heart failure.
4. Isoproterenol administration to increase cardia output (if needed).
5. Oxygen may be given.
6. Other procedures as necessary may be used.
7. Continue to monitor kidney and brain functions.

 

Adaptation of Endurance Training

Endurance training connotes a process of adaptive changes to achieve the strength, power and cardiorespiratory capacity to complete the specific physical task. Endurance training requires several months of rhythmic and continued exercise that results in an increase in the body’s number of capillaries, maximal oxygen uptake, stroke volume, and enzymes. Moreover, endurance training increases the sectional size of slow type fibers and there is an actual conversion of fast type fibers (Type 11B.) to slow (Type 11A.). The Type 11B. fibers are the fast fibers, and are capable of lasting longer than the type 11A. fibers. Therefore, there are major underlying biochemical changes in the various organs and cells involved in the physical activity that provides the needed energy, strength and power to carry out the task. Soccer requires a combination of slow and fast fibers because soccer playing is a combination of quick actions lasting less than 1-2 minutes and a prolonged activities which can last 5-10 minutes.

Athletic physical conditioning has become a very serious and scientific endeavor. In the past 20 years, there has been an increase in our understanding of the physiology and biochemistry of exercise. There has also been an increase in interest in the mechanism of how exercise induces physiological and biochemical adaptation at the cellular and organismic level and how this accounts for the improved performance of athletes in a given sport.(1)

Endurance in sports means the ability of the person to perform a specific prolonged exercise or work to achieve a reasonable task without adverse reactions such as fatigue, exhaustion, and injury. Endurance can mean different things for different tasks (i.e. sport activity), as each task may involved unique muscle groups and skill levels. Therefore, there are several components of endurance that develop differentially during endurance repetitive training for the specific sport. The components of endurance are: muscle strength and power, the cardiovasculatory system, and the respiratory system. The cardio-respiratory endurance is needed with varying intensities in all sports. However, strength and power can vary in magnitude from muscle to muscle. Therefore, local endurance is quite important for a given sport. During endurance training of repetitive exercise for several months, the muscles adapt to generate force and to maintain a supply of energy. The key factor in endurance training is the exertion of physical stress with certain frequency and for lengths of time. This chronic muscular activity stimulates growth of the muscle as well as the development of endurance in terms of oxygen delivery, energy production, and permanent metabolic and structural changes. Therefore, endurance training in this context is a low-level, prolonged-intensity aerobic training exercise where the system can utilize oxygen as the initial trigger of energy source. The first general aspect of endurance adaptation is the adaptation of the cardiovascular/respiratory system to accommodate the increased frequent demand for oxygen uptake and delivery.

Cardiovascular – Respiratory Adaptation

Rhythmic and continued exercise requires a greater use of oxygen at the muscle site. Therefore, the routes of uptake and transport of oxygen from the air to muscle tissues must adapt to the increased rate of delivery and extraction. A measurement of cardiorespiratory endurance is the VO2 max. VO2 max is the maximal oxygen uptake during the maximal exercise, and it differs from person to person. In order to compare exercise-related data from person to person, the data is expressed relative to a specific level of intensity of exercise and represented as expressed as a percent of VO2 max. To illustrate its importance, endurance training can change the VO2 max by as much as 20%. This is the first indication that true structural and biochemical changes must occur in order to metabolize the increased oxygen uptake. The first apparent result of an exercise is the immediate increase in heart rate. The resting rate is 80 beats per minute; however, during exercise the heart rate can go as high as 190 beats per minutes. After several months of endurance training, heart rates can go as low as 40 beats per min. This reflects several factors of adaptation to exercise among them being the autonomic nervous system. However, the one aspect related directly to the heart rate is the fact that despite the lowered heart rate, the heart provides a greater cardiac output because the stroke column increases by as much as 80%. In a highly trained athlete, the refilling is more complete. More importantly, the left ventricle strength and power is dramatically increased. The left ventricle undergoes hypertrophy with endurance training, which means the actual heart muscle mass and volume are increased. Heart size is greater in endurance trained athletes by as much as 25%, as compared to a sedentary person. Moreover, the contraction of contractile proteins are increased and the composition of the protein changed. Also, oxygen delivery of the blood supply to the heart is improved because the number and size of capillaries per cross-sensational areas of muscle increases by as much 50% due to endurance training. Endurance training also improves (by as much as 80%) the muscle content of myoglobin. Myoglobin carries oxygen within the muscle tissue. These dramatic biochemical adaptations in the oxygen delivery system parallels those of the heart and thus complements the entire scope of the biochemical adaptation for a better performance by the trained athlete.(2)

Blood Volume and Composition

There are three major changes in the blood due to endurance training: (1) increased blood volume; (2) increased hematocrit (i.e. increase in the total number of red blood cells (RBC); and (3) decrease in viscosity. The increased blood volume is as high as 20%. However, the increase in RBC is less pronounced and as a consequence the viscosity of the blood decreases. The increase in blood volume is the key important factor for an endurance trained athlete. The increased blood volume enhances O2 delivery as well as enhancing microcirculation. The increase in microcirculation is even more pronounced due to the blood’s reduced viscosity. A trained athlete also has another advantage in greater capacity to clear lactate from the muscle and utilizing lactate as an energy substrate. Thus, the level of blood lactate in a trained athlete is lower than in a sedentary person. This phenomenon is referred to as a lactate shift. A trained athlete therefore has a greater endurance with less fatigue and cramps due to decreased levels of blood lactate.

Common Injuries Encountered in the Sport of Soccer

The physiological principles of tissue damage and tissue healing are essentially the same for all sports. What makes each sport somewhat unique in terms of the injuries encountered is the specific sport activities which lead to specific mechanisms of injury. The soccer skills involved with passing and dribbling, kicking, ball control, heading, tackling and goal keeping all, when combined with the principles of force, gravity, ground contact, and torque, can lead to injuries.

Unfortunately and wrongly, our youngest athletes (such as youth soccer players) receive the least sports medicine coverage. Therefore, injury recognition and evaluation becomes the premise of the coach or parent who may have little or no preparation for the task.

In an attempt to simplify the evaluation procedures, the most basic acronym, HOPS, should be employed. HOPS stands for history, observation, palpation and strength/sensation. This primitive evaluation system may be utilized with any type of injury.

A good preparticipation physical examination is mandatory. This provides the benchmark from which deviations from the norm may be measured. A good preparticipation physical should minimally include a medical history, height and weight check, visual acuity check or screen, orthopedic or joint evaluation and visceral examination. Physicians specializing in sports medicine are the best sources for these physical exams.

Observation begins the first time one sees the injured athlete. Is he/she conscious, does the athlete walk with an antalgic gait, does the athlete hold any body part as a protective manner, and is the athlete visibly exhibiting pain? These are all important observational factors. Also, if one is dealing with an extremity injury, the evaluator should visibly compare that limb to the contralateral or uninjured limb.

Palpation involves touching and moving the injured body part. If pain is diffuse, palpation may be of limited value. However, if the pain is specific or point tender, then active, passive and resitive motion will assist the evaluator in localizing the injury site or injured structure.

Strength/sensation is the final aspect of the field evaluation. Again, if dealing with an extremity injury, one has the luxury of being able to compare strength and sensation of the injured limb to that of the uninjured.

Common injuries encountered in the sport of soccer include:

  •  

    Sprains: A sprain represents damage to a ligament. Common sprain sites include the ankle, knee and wrist.

  •  

    Strains: A strain represents damage to a musculotendinous unit. Common strain sites encountered in soccer include the gastrocnemius, quadriceps, hamstring, low back and shoulder.

  •  

    Fractures: Common fracture sites include the fingers, tibia, fibula, radius and ulna. These fractures are usually resultant from falls. The only method of positive fracture diagnosis is X-ray.

  •  

    Dislocations: Dislocation sites commonly encountered may include fingers, should and elbow. The most common mechanism of injury resulting in a dislocation is the fall on the outstretched hand or arm.

  •  

    Contusions: Contusions are resultant from contact with the ball, with other players, or with the ground.

  •  

    Concussions

 

When does an injury need to be referred to a physician? Although this is a difficult question to answer, the following guidelines will assist the layman in making the decision:

 

1. Suspicions of a fracture
2. Suspicions of a concussion
3. An injury in which the pain cannot be controlled with conservative measures
4. A laceration that may require sutures
5. Any suspicion of internal injury

 

Additionally, any time the layman is unsure of his/her evaluation, the athlete should be referred to a physician.

Conservative Care of Acute Injuries

The acronym PRICE represents a form of conservation care for acute injuries.

“P” stands for protection. An ankle injury can be protected by placing the athlete on crutches non-weight bearing.

“R” stands for rest. Rest means not using the injury body part and allowing it to heal properly.

“I” stands for ice. Ice or cold is utilized in cryotherapy. The use of ice results in a greater chance of tissue survival, reduces degradation of healthy tissue, induces vasoconstriction which prevents further swelling and loss of range of motion and enhances early mobilization. Ice also acts as a topical anesthetic.

“C” stands for compression. Specific compression when applied to an extremity injury may prevent swelling and the accompanying loss of range of motion.

“E” stands for elevation. By elevating an extremity injury, once reduces effusion and dependent bleeding. Again, this reduces swelling and loss of range of motion, both of which tend to protract injury recovery time.

Remember, the whole idea behind the science of sports medicine is to provide the best possible environment for healing to occur.

Summary

Youth and age group soccer can be an extremely positive experiences for the young athlete. Skill development, coordination, socialization skills, and cooperation are all positive results of a healthy youth and age group soccer program.

In order to assure a healthy program, one must insist that sports medicine considerations such as preparticipation physical exams, proper conditioning, conservative injury care and warm- up and cool down periods are observed as well as adequate hydration and rehydration.


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