This is an excerpt from Soccer Anatomy-2nd Edition by Donald T. Kirkendall & Adam L. Sayers.
One of the purposes of a preparticipation physical examination is to identify factors that might predispose a player to an injury. Many issues need to be considered when acting on what is identified in this examination. In general, injury risks can be categorized as intrinsic (for example, age, prior injury, strength, neuromuscular skill, and more) or extrinsic (such as equipment, environment, playing surface, officiating, opponents, etc.); many injuries aren't an either/or consideration because, as you'll see, intrinsic and extrinsic risks interact with each other. Finally, some injuries are simply an accident that no one can predict.
A torn ACL is one of the most feared injuries and can happen with or without any direct contact to the knee. The noncontact tear of an ACL requires many little things to come together at just the right time, mostly during cutting or landing. During the numerous training hours and matches, players will cut and land thousands of times. In the presence or absence of identifiable risk factors, why did the ACL fail this specific time? A question without a good answer.
There are two simple ways to prevent injury: improve fitness and improve skill. The skilled, fit player is injured far less often than the unskilled, unfit player. And if poor fitness is related to injury, the onset of fatigue must also be a factor. Overall injury rates increase with time during a match. In most studies, around 25 percent of all injuries happen in the last third of the second half. Additionally, most injuries happen during preseason training when the players are less fit and working hard to improve their fitness. Once the competitive season begins, the days of hard training are less frequent, and the injury rate declines. Another fatigue-related factor is the training-to-match load ratio. The smaller this ratio (meaning a congested schedule of fewer training days in preparation for each match), the greater the injury rate. A final fatigue-related issue is one that applies to teams with longer seasons than typically seen in the United States. Ekstrand, Spreco, and Davison (2018) show that leagues without a winter (midseason) break have more injuries in the second half of the season than leagues with that break.
Age is a factor in certain injuries. For example, hamstring strains are more common in older players, while ACL tears are more frequent in younger (middle or high school) players. As with many injuries, however, the susceptible age for a hamstring strain seems to be dropping.
If age is an issue, so is gender. Females have a greater risk for ACL tears and head injuries than their male counterparts. Another age-related concern is the growth spurt of adolescence. Growth (especially in boys) is linear (up) first followed by circumferential (muscle mass). That tall gangly boy who has quickly grown tall but has not yet filled out is at a greater risk for injury than other same-age teammates who have yet to hit their growth spurt (the late maturers) or those who have already gone through their growth spurt (the early maturers).
Strength, flexibility, and balance are issues in most every injury. Preseason evaluations usually test each leg separately for these factors, and test results are rarely symmetric; one leg is often “better” than the other. For example, most players will have a preferred leg (limb dominance) that will usually test better than the other leg. (How is the dominant leg determined? Is it the preferred kicking leg or the preferred leg to do a long jump? It's not always the same.) It is interesting that more injuries happen to the dominant leg. When imbalances are evident, corrective training can minimize limb differences and prevent some injuries.
One of the main aspects of the preparticipation exam is to identify each player's injury history. A prior injury is one of the strongest predictors of a future injury. If an athlete has previously suffered from a sprained ankle, chances are good that another ankle sprain will happen. The risk of a reinjury can be as low as 1.5 times for an ankle sprain or as much as 5 times for an ACL tear. When the next injury might happen is unknown.
With 11 field positions, injuries vary according to player position. Defenders have the most injuries followed by strikers. Midfielders and goalkeepers are the least injured. Previously injured players often enter back into the lineup by playing a position with a lower chance of injury.
Once a player is injured, a rehabilitation period begins. We will not be discussing how injuries are rehabilitated nor will we outline the criteria necessary to return to activity, training, or competition, although returning to activity, then to training, then to competing, then back to full preinjury level of competition is currently a very hot research topic.
Before most international matches will be a display of FIFA's Fair Play banner. Players and coaches make a pledge to play according to the Laws of the Game. This is not an idle slogan. At the professional and international level, roughly 40 percent of all injuries occur during foul play, so adherence to these laws prevents injury. Coaches need to continually instruct players to stay on their feet (despite what they see on TV). Tackles during which the defender leaves his feet (and generally has his studs up) puts both players at risk for an injury and the tackler at risk for a red card.
Most of the injury research (and chapters like this one) addresses acute injuries, injuries with a specific identifiable event. Another class of injury is the so-called overuse injury, injuries without a specific identifiable event. A minor tweak may become an annoyance that is not treated, and training continues. At some point, the pain becomes sufficient enough that the player seeks medical attention. These training-induced injuries slowly become more limiting; if the constant progression of the training load makes things worse, the best treatment is reducing the training load through rest. Rapid progression of training loads increases the risk of an overuse injury, but this is a topic for another book!
For both preinjury prevention and postinjury rehabilitation, compliance to the prescribed programs is critical. Prevention activities are effective only when done regularly and should never be considered a novelty to break up the monotony of training. After an injury, every player wants to get back as soon as possible. We can't possibly detail the complete list of training exercises and regimens that have been tested and proven to be effective. Most certified athletic trainers and physical therapists can provide those details. Athletes return to play sooner when the therapist's instructions are followed exactly. Don't try to return too quickly; returning too early from a seemingly minor injury puts the player at a high risk for another, usually more severe, injury.
Finally, plenty of injuries are simply accidents—a purely random occurrence. A player may miskick the ball that then strikes the side of an unsuspecting player's head. The resulting angular acceleration can cause a concussion. A player may jump and land on another player's foot, resulting in a sprained ankle for the jumping player. Neither situation can be predicted.