• Soccer, or football, is the world’s most popular sport. Although its origins trace back over 3000 years, the current organized form of soccer originated in 1863 in Britain.

  • Federation Internationale de Football Association (FIFA) is the governing body for soccer in the world, and it includes 211 affiliated national associations. There are six different confederations within FIFA, and the United States is a member of the Football Confederation in North and Central America and the Caribbean (CONCACAF).

  • The laws of the game are formed by the International Football Association Board (IFAB), which was formed in 1886 for this purpose. According to FIFA, there are 265 million registered soccer players in the world, including 26 million females and 22 million youth participants. Between 2000 and 2006 there was a 21% and 254% increase worldwide in the number of male and female participants, respectively, that registered.

  • The popularity of soccer has steadily risen in the United States, with over 25 million Americans playing at all levels.

  • Professional soccer in the United States includes Major League Soccer (MLS), United Soccer League (USL), and the National Women’s Soccer League (NWSL). In 2021 the MLS will have 28 teams, USL has more than 100, and the NWSL has 9 teams. MLS has more diversity than any other professional male sport league in North America, with players from more than 70 countries.

General Principles

Rules of the Game

  • Objective of the game: To win the game by outscoring your opponent, which is achieved by hitting the ball into the opponent’s goal

  • Game lasts for 90 minutes; divided into two 45-minute halves

  • Eleven players on the field—10 field players and one goalkeeper

  • The ball cannot be played by the hands (except goalkeeper), but all other surfaces of the body can be used.

  • Rules protect against rough play—there are direct and indirect fouls.

    • Direct fouls include kicking the opponent, tackling from behind, using hands, and pushing.

    • Indirect fouls include offside, obstruction, and certain unintentional fouls.

    • Offside rule: must have two players between an offensive player and the goal; this often includes the goalkeeper

  • Required equipment: Ball, uniforms, and goalposts; most leagues require shin guards

  • There are different methods of putting the ball back in play when it goes out of touch (out of bounds):

    • Throw in: when the ball goes out over the sideline

    • 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

    • 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

Sport-Specific Demands and Skills

  • Physical demands: Players engage in discontinuous, high-output activity that involves aerobic and anaerobic metabolism.

    • At the elite level, players typically cover 8–10 km during a game, making soccer an endurance sport. Two-thirds of this distance is spent in low-intensity activity such as walking and jogging.

    • The aerobic system is heavily involved, with heart rates around 85% of the maximum rate and oxygen demand about 70% of maximum oxygen uptake (
      V ˙
      O 2 max).

  • 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.

    • 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, which may be associated with traumatic injury such as a sprain of the medial collateral ligament (MCL).

      Figure 67.1, Soccer-specific demands and skills. (Photographs © 2008 Beverly Schaefer.)

    • Outside of foot pass/shot: Internal rotation of the leg, foot in inversion, plantarflexion. Results in increased risk of forceful inversion plantarflexion injuries, mid/forefoot injuries, ligament sprains, and peroneal tendon problems (see Fig. 67.1 ). In younger athletes, this may lead to apophysitis or avulsion fractures.

    • Instep of foot: Extreme plantarflexion in “locked” foot, hip flexors, quadriceps, rectus, and hamstrings (see Fig. 67.1 ); ball velocity at release is between 17 and 28 meters/second.

    • 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.

    • 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.

    • 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 )

    • Appropriate technique is important in all skills to avoid and decrease injuries.

Factors Affecting Performance and Recovery


  • 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.


  • Occurs when sweat losses exceed fluid intake, which is particularly a concern in warm weather

  • 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.

Heat Illness

  • Risk factors for development of heat illness include preexisting medical disease, age, poor conditioning, inadequate acclimatization, dehydration, obesity, fatigue, prior heat injury, febrile illness, and medications.

  • Modifications should be made to decrease the risk of heat injury: more water breaks, change game times, and shorten the length of play.

  • Studies have investigated the effect of hyperhydration on improving thermoregulation.


Carbohydrate Intake

  • Glycogen constitutes the major energy source for muscles.

  • Muscle glycogen is depleted within 90–180 minutes of exercise at 60%–80%
    V ˙
    O 2 max or 15–30 minutes of exercise at 90%–130%
    V ˙
    O 2 max. Glycogen stores take approximately 2–3 days to fully recover.

  • Athletes need 10–12 g of carbohydrate per kg/day to maximize glycogen stores (see Chapter 5: “Sports Nutrition”).

  • Numerous studies have looked at the difference between a low- vs. high-carbohydrate diet and have consistently shown an increase in total distance covered in addition to an increase in high intensity and intermittent running with a high-carbohydrate diet.


  • Refers to physical and mental restoration to maximize performance and minimize potential for injury

  • Active recovery

    • Active recovery, often referred to as cool-down or warm-down, after the conclusion of intense exercises is widely used despite the lack of clear evidence supporting its benefits.

    • Whereas numerous studies have found that active recovery enhances removal of blood lactate, other studies have reported decreased glycogen stores with this strategy.

Cold-Water Immersion

  • Cold-water immersion (CWI) has gained tremendous popularity among athletes to minimize fatigue and enhance postexercise recovery.

  • CWI protocols typically involve immersion into 48.2°F–50°F (9°C–10°C) water for 5–20 minutes immediately after exercise.

  • Studies have suggested an effect on short- and long-term recovery by:

    • Ameliorating hyperthermia and rapidly reducing the body temperature, which, in turn, decreases central nervous system (CNS) fatigue and possibly decreases cardiovascular strain

    • Facilitating the removal of muscle metabolites, which may lead to delayed-onset muscle soreness

    • Enhancing parasympathetic reactivation, which leads to a decrease in heart rate and is associated with improved long-term recovery

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