Soccer: Leg injury risk factors (pt 1)

In the grand scheme of things, sports injuries do not have the public health impact of heart disease, arthritis or any number of chronic conditions. But the estimated worldwide cost of sports injuries is in excess of $1 billion for the 3 million to 5 million injuries that happen each year.

Just from an economic standpoint, prevention of injuries would have a substantial impact. The athletes themselves would like to prevent injuries so they can keep playing. The doctors and coaches also want to see fewer injuries.

It is hard to believe that anyone would speak out against prevention studies and programs. FIFA's research arm, F-MARC, is initiating a nationwide injury prevention study in Switzerland, "for the good of the game."

When research on injury prevention is performed, a primary focus is on pre-injury risk factors. This kind of work began in earnest with research on heart attacks, and certain risk factors were identified. The implication was that if people modified their risk factors, then the risk of heart disease would be reduced. The same concept applies to sports injuries.

The research identifies two basic sports-injury risk factors: extrinsic and intrinsic. Extrinsic factors are those that exist in the setting where the athlete competes -- field, temperature, environment, etc. Intrinsic factors are those that exist within the athlete.

Intrinsic factors can be divided into two classes: modifiable and non-modifiable. Modifiable intrinsic factors include fitness and flexibility. Non-modifiable factors are things the athlete was born with, things like limb length inequality, sex, Q angle, etc. This article will examine extrinsic factors affecting spots injury, and the next will be about intrinsic factors.

Extrinsic factors

Some of these factors may be under the control of the athlete and some aren't. And much of the data was collected on military recruits, where experimental control and medical care is well-maintained.

Level of competition

Nearly every study on sports injury shows that the higher the level of competition, the greater the injury rate. Recreational soccer has a low injury rate, while the traveling leagues have a higher rate of injury and the pros have a still higher rate.

In England, the injury rate of the pros is over one injury per player per season. A high school team might see one concussion every four or five seasons, while top-level college teams may see one per season.

Also, games are far more dangerous than practice; a fairly obvious observation. These patterns are seen for both males and females in most sports, soccer included. The time of season is also a factor. Many injuries occur in the very early weeks of the season and also later in the season.

Skill level

This one can be confusing. Two studies show that athletes with lower skill were at a twofold risk of injury when compared with higher-skilled athletes. But then, two other studies show that the higher-skilled players were at an increased risk of injury. Research methodology may be an explanation.

Anyway, one could argue that the higher-skilled players play at a higher intensity. One could also argue that the lesser-skilled players don't play as often but have the same number of injuries, leading to an increased rate of injury due to reduced exposure.

I might throw in one other factor: I have no data on this, but I have noticed that when highly skilled players play with lesser-skilled players, the one who usually gets hurt is the highly skilled player, mostly from the rookie carelessly running into the veteran or making a poor tackle.

Shoe type

Over 30 years ago, it was shown that football players wearing the traditional 14-studded molded sole soccer shoe had far fewer knee injuries than players wearing the traditional 7-stud football shoe. About five years ago this was again demonstrated: Players wearing a hybrid shoe of round studs in the center and rectangular studs around the edge of the sole sustained more knee injuries than those in molded-sole soccer shoes.

There also are anecdotal reports of fewer ankle sprains in athletes wearing a 3/4 or high-top shoe.

Ankle braces

A well-controlled clinical trial showed that the use of an ankle brace led to a threefold reduction in ankle injuries. Another project showed that ankle braces were not effective at reducing an athlete's first ankle sprain, but were highly effective at preventing a re-injury in those with a history of ankle sprain.

Still another project added some preventive training to the mix and showed that the training was as effective as the brace, and both were far better than nothing. The use of tape as a preventive is well-known, but it appears that the tape improves the awareness of the athlete rather than actually doing anything to the ankle. The role of taping or bracing on knee injury is unknown.

Playing surface

Two studies have compared injury rates on artificial turf vs. grass and have shown that there are more ankle and knee injuries on artificial turf, attributable to the increased friction and traction.

By the same token, the condition of a grass field can influence injuries. A poorly cared-for field will have players stepping in divots, potholes, cuts, holes etc. This can lead to foot and ankle injuries because they are stepping into an unknown. They expect to hit smooth grass, but hit a hole instead. Ever been caught not paying attention while walking downstairs and thought there were four steps but there really were five? You thought you were going to hit the floor, but instead you end up nearly falling, as the floor wasn't where you thought it would be. The same thing can happen on a poorly maintained field.

It is well-known that ACL injuries are not very common when playing on wet fields, while muscle strains are more frequent.

Based on this extrinsic list, how does one prevent injuries? For one, play with and against people of your own skill level. Improve your skill. Wear a multi-studded molded sole shoe (for youth, like age 5 to maybe age 10, I wouldn't even put studded shoes on them, but the player might not go for that if the rest of the team wears studs).

Ankle braces are effective at reducing ankle injuries, especially in those with a history of ankle injury. And ankle braces have not been shown to diminish performance. Finally, as most players play on grass, make sure the fields are well-maintained.

Next: Intrinsic causes of injuries

Copyright (c) 2003 Donald T. Kirkendall

Donald Kirkendall has a Ph.D. in Exercise Physiology, and is on the faculty in the Department of Orthopaedics at the University of North Carolina. He is a Fellow in the American College of Sports Medicine. He has coached soccer for ages U10 through college, and is on the USSF Medical Advisory Committee. He's edited seven books in exercise science and sports medicine, and has published numerous articles on soccer and sports sciences.

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