General Principles
Rules of the Game
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Objective of the game: To win the game by outscoring your opponent, which is achieved by hitting the ball into the opponent’s goal
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A game lasts for 90 minutes; divided into two 45-minute halves
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11 players on the field—10 field players and one goalkeeper
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The ball cannot be played by the hands (except goalkeeper), but all other surfaces of the body can be used.
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Rules protect against rough play—there are direct and indirect fouls.
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Direct fouls include kicking the opponent, tackling from behind, using hands, and pushing.
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Indirect fouls include offside, obstruction, and certain unintentional fouls.
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Offside rule: must have two players between an offensive player and the goal; this often includes the goalkeeper
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Required equipment: Ball, uniforms, and goalposts; most leagues require shin guards
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There are different methods of putting the ball back in play when it goes out of touch (out of bounds):
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Throw in: when the ball goes out over the sideline
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Goal kick: when the ball goes out over the endline, last touched by an offensive player; kicked in from the goal box by the defensive team
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Corner kick: when the ball goes out over the endline, last touched by a defensive player; kicked in from the field corner by the offensive team
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Sport-Specific Demands and Skills
Physical demands: Players engage in discontinuous, high-output activity that involves aerobic and anaerobic metabolism; activity further divided into sprinting, cruising, running, and walking
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Energy expenditure requires approximately 75% V̇O 2 max; differs with position (midfielders expend more energy than those in other positions); average heart rate: 165 beats per minute. Players typically cover 8–12 km during a game.
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Ratio of time spent in low-intensity versus high-intensity efforts is 7:1.
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Sprints occur once every 90 seconds; high-intensity efforts (cruise and sprint) once every 30 seconds; only 2% of the total distance covered involves time spent with the ball
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Physiologic demands: Implications for thermoregulation and nutritional needs; energy needs increased by sport-specific skills
Strength demands: High demand on trunk and lower extremities; most skills require balancing on one leg, which emphasizes lower extremity strength and proprioception.
Soccer specific skills: Various surfaces of the lower extremity are used to strike or control the ball and tackle, thus putting various structures at risk.
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Inside of foot pass/block tackle: Foot and hip externally rotated, knee flexed, foot “locked” in dorsiflexion ( Fig. 67.1 ); results in significant valgus stress at the knee and may be associated with traumatic injury (sprain of medial collateral ligament [MCL], fracture) or muscle strain
Figure 67.1
Soccer-specific demands and skills.
(Photographs © 2008 Beverly Schaefer.)
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Outside of foot pass/shot: Internal rotation of the leg, foot in inversion, plantarflexion; may place an athlete at a risk of forceful inversion plantar flexion injuries, mid/forefoot injuries, ligament sprains, and peroneal tendon problems (see Fig. 67.1 ); in young athletes, this may lead to apophysitis or avulsion fracture.
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Instep of foot: Extreme plantar flexion in “locked” foot, hip flexors, quadriceps, rectus, and hamstrings (see Fig. 67.1 ); ball velocity at release is between 17 and 28 meters/second.
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In the approach and ball strike phase of an instep kick, a varus torque of >200 Newton meters (Nm) and extension torque of >280 Nm is generated on the proximal tibia.
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A total of 2000 Nm is generated during a soccer kick. Only 15% is transferred to the ball; the remainder is absorbed by the eccentric contraction of the hamstrings.
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Kicking the ball on the ground can injure the forefoot, ankle, and toes (particularly the great toe).
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Heading: Purposeful, forceful striking of the ball with a player’s head to control, clear, or redirect on goal; increases the risk of head and neck injuries because of player contact (head to head or other body part, or head to goal post or ground) that occurs while fighting for possession in the air (see Fig. 67.1 )
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Appropriate technique is important in all skills to avoid and decrease injuries.
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Factors Affecting Performance and Recovery
Fatigue
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Fatigue or decreased performance in soccer players is multifactorial—can be related to environmental or nutritional factors including dehydration, glycogen depletion, aerobic fitness, and mental fatigue.
Dehydration
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Occurs when sweat losses exceed fluid intake, which is particularly a concern in warm weather
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A decrease in performance is noted when there is fluid loss of >2% of an athlete’s body weight. At >3% loss, more serious consequences can arise such as exertional heat illness.
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A study following soccer players over a 2-week training period showed that on average, athletes drank approximately 2.7 L of fluid on their own. V oluntary intake resulted in a deficit of 1.1 L, which is not enough to meet needs.
Heat Illness
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Risk factors for development of heat illness include pre-existing medical disease, age, poor conditioning, inadequate acclimatization, dehydration, obesity, fatigue, prior heat injury, febrile illness, and medications.
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Modifications should be made to decrease the risk of heat injury: more water breaks, change game times, and shorten the length of play.
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Studies have investigated the effect of hyperhydration on improving thermoregulation.
Nutrition
Carbohydrate Intake
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Level of muscle glycogen stores before exercise important
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Muscle glycogen is depleted with 90–180 minutes of exercise at 60%–80% V̇O 2 max or 15–30 minutes of exercise at 90%–130% V̇O 2 max, performed in intervals of 1–5 minutes.
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Athletes need 10–12 g of carbohydrate per kg/day to maximize glucogen stores ( Chapter 5 , Sports Nutrition).
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Comparison of soccer players with high versus low prematch muscle glycogen content:
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Low glycogen group covered 24% less total distance (most at high speeds).
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Players with low pregame values had no glycogen stores at end of game compared with 10% of remaining glycogen stores in players with high pregame values.
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One study looked at the effects of a high-carbohydrate diet (65% of calories) versus low-carbohydrate diet (35% of calories) on technical and physiologic variables.
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Technical variables included number of successful/unsuccessful “green” (low-risk, nonpenetrating) and “red” (high-risk, penetrating) passes and total number of touches per possession.
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After a high-carbohydrate diet, higher pregame muscle glycogen content was observed along with 33% more high-intensity work. No difference noted in any technical variables.
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Recovery
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Often refers to physical and mental restoration that leads to performance readiness; it employs multiple tools to enhance performance
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Active Recovery
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A study evaluated the use of a “cool down” period, performed by 81% of French professional soccer teams and involved a strategy of either running, biking, or swimming for 15–30 minutes after a match and found that this enhanced blood lactate removal compared with passive recovery.
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However, other studies identified decreased glycogen stores after this strategy. No effect was noted on oxidative stress markers.
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Unclear at this point if active recovery is beneficial or detrimental.
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Cold-Water Immersion (CWI)
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Cold-water immersion (CWI) has gained tremendous popularity among athletes to minimize fatigue and enhance postexercise recovery.
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There are various CWI protocols; typically involves immersion in 9°C–10°C water for 5–20 minutes immediately after exercise.
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Studies have suggested an effect on short- and long-term recovery by:
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Ameliorating hyperthermia and rapidly reducing the body temperature, which, in turn, decreases CNS fatigue and possibly decreases cardiovascular strain
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Facilitating the removal muscle metabolites, which may lead to delayed-onset muscle soreness
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Enhancing parasympathetic reactivation, which leads to a decrease in heart rate and is associated with improved long-term recovery
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General Injury Patterns
Overall Injury Incidence
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Overall injury incidence in soccer is favorable (much lower than in American football).
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Number of injuries increases as skill and age increase—low levels of injuries are seen in children aged <10 years, with the rate increasing 10-fold at the high school level.
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At younger age levels, girls are noted to have a higher incidence of injury than boys ( Table 67.1 ).
TABLE 67.1
INJURIES IN SOCCER PER 1000 PLAYER HOURS: BOYS VERSUS GIRLS
Study
Girls
Boys
Engstrom et al., 1991 *
12
5
Nilsson and Roaas, 1978
32
14
Maehlum et al., 1986
17.6
8.9
Schmidt-Olsen et al., 1991
17.6
7.4
Powell 1999 (injuries/1000 AEs)
5.3
4.6
* Denotes studies using time loss from practice/play as definition of injury.
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At the collegiate level, gender differences are less striking, with the exception of anterior cruciate ligament (ACL) injuries.
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National Collegiate Athletic Association (NCAA) data from 2004/05 to 2008/09 seasons showed an overall injury rate of 7.7/1000 athlete exposures (AEs) in men’s soccer and 7.3/1000 AEs in women’s soccer.
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Lower limb injuries (ankle, knee, and upper limb) were most common and accounted for 65.6% of men’s injuries and 65.3% of women’s injuries ( Table 67.2 ).
TABLE 67.2
NCAA DATA OF INJURY PERCENTAGE BREAKDOWN FROM THE 2004/05 TO 2008/09 SEASON
Men’s Soccer
Women’s Soccer
Concussion
5.5%
Concussion
9.2%
Head, face, neck
4.3%
Head, face, neck
4.1%
Upper limb
6.2%
Upper limb
5.6%
Torso and pelvis
14.7%
Torso and pelvis
12.3%
Lower limb
65.6%
Lower limb
65.3%
Other
3.7%
Other
3.5%
Adapted from NCAA Data, 2004–2005 through 2008–2009; National Collegiate Athletic Association.
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Soccer players are three times more likely to be injured in a game compared to practice ( Table 67.3 ).
TABLE 67.3
INJURY DATA FROM NCAA INJURY SURVEILLANCE SYSTEM 2009–2010 THROUGH 2013–2014
Sport
Event
Avg Annual Estimate of Injuries
Avg Annual Estimates of No. of Athlete-Exposures
Estimated Injury Rate Per 1,000 Athlete-Exposures
Men’s Soccer
Competition
6,458
360,880
8.0
Practice
6,977
1,323,974
Overall
13,435
1,684,854
Women’s Soccer
Competition
7,434
432,347
8.4
Practice
7,679
1,367,650
Overall
15,113
1,799,997
Adapted from Kerr ZY, Marshall SW, Dompier TP, Corlette J, Klossner DA, Gilchrist J. College Sports-Related Injuries—United States, 2009-10 Through 2013-14 Academic Years. MMWR Morb Mortal Wkly Rep. 2015;64(48):1330-1336.
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Female soccer players noted to have a higher incidence of ACL injuries compare to their male counterparts.
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A 2005 study by Angel et al. reviewed ACL injuries in NCAA male and female basketball and soccer athletes from 1990 to 2002 and found that females sustained 67% of all noncontact ACL injures compared with 58% in males.
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Injury patterns are similar for indoor and outdoor soccer.
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Goalpost injuries can be fatal; should be preventable.
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In the US during 1980–1994, 27 injuries were caused by falling goalposts, with 18 fatal cases (14 involved head trauma).
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Injury Surveillance System (ISS)
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NCAA has used the Injury Surveillance System (ISS) to collect injury and exposure data from intercollegiate athletes since 1982. Injury is defined as time loss.
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Advantages : Data are shared with NCAA sport and policy committees as well individual institutions to make evidence-based decisions regarding health and safety issues.
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Disadvantages of ISS : Injuries without time loss are missed, certain injuries may not be “time loss injury” (i.e., no time loss if in season, but time loss if off season).
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Despite these limitations, ISS data provide a denominator (number of AEs) and are thus useful for comparing sports, genders, and injury types.
Indoor Soccer
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Patterns may differ slightly, but in general, type, location, and severity of injury appear similar in outdoor and indoor soccer.
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Injury data sparse; only two studies provide a denominator and include women.
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A 1996 study looked at the Lake Placid Dawn to Dark Festival (3-day indoor tournament)—injury incidence for men was 5.79 per 100 player hours and for women was 4.74. No significant difference in incidence of injury between men and women; no difference in knee injuries. Severe injuries were more likely to be noncontact; 71.4% injuries were in lower extremities.
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Data evaluating injury incidence, severity of injury, and mechanisms of injury on natural grass versus third generation artificial turf by male and female players demonstrated no significant differences between these surfaces.
Prevention of Injuries
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In recent years, the Fédération Internationale de Football Association (FIFA) and its Medical Assessment and Research Center (F-MARC) have developed injury prevention programs such as the FIFA 11 and FIFA 11+ programs.
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FIFA 11+ is a restructured program that addressed the compliance issues and inadequate therapeutic exercises of the original FIFA 11 program.
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FIFA 11+ consists of a 20-minute warm-up program that should be performed twice a week before each training session. Before a match, only running exercises should be performed.
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Studies evaluating the efficacy of this program in varied settings (high school, collegiate, and professional levels) have showed lower extremity injury prevention by up to 30%–50%.
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Extensive research has been performed specifically targeted toward ACL injuries in women and incorporates the use of neuromuscular (NM) training.
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Hewett et al. (1999): 60- to 90-minute training sessions 3 times per week for 6 weeks in soccer, volleyball, and basketball resulted in a 72% decrease in noncontact ACL injuries.
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Mandelbaum et al. (2005): Studied the Prevent Injury and Enhance Performance Program (PEP), which emphasized proprioception and NM training. The program included 20 minutes of soccer-specific agility drills, plyometrics, lower extremity and trunk stretching, and strengthening exercises. A 74% reduction in ACL tears was seen over 2 years (see Recommended Readings ).
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