Injury is a fact of life for most athletes, but some professionals—and some weekend warriors, for that matter—just seem more injury-prone than others. But what is it about their bodies that makes the bones, tendons, and ligaments so much more likely to tear or strain—bad luck, or just poor preparation?

A growing body of research suggests another answer: that genetic makeup may play an important role in injury risk.

A review article recently published in the Clinical Journal of Sports Medicine emphasizes that research on the genetics of sports injuries “holds great potential for injury prevention for athletes at every level.” The authors, from Stanford University’s department of developmental biology and genetics, believe that genetic testing also gives athletes valuable information that might increase their competitive edge.

Stuart Kim, one of the study’s authors and a professor of genetics at Stanford, says his interest in sports injuries began almost by accident. “I initially intended to study the genes associated with the large size of NFL lineman, but the athletes weren’t really interested in finding out the genetic reasons why they were so big,” Kim says. “But they were extremely interested in figuring out what injuries they were more likely to sustain.”

Genetic information can be valuable for amateur athletes, too—regardless of skill level, someone about to join a recreational basketball league or a tennis club would be well-served to know if they’re at risk of blowing out an ACL or tearing an Achilles. Each year, around 2 million adults go to the emergency room for sports-related injuries, many of them acquired during pickup games or matches in recreational leagues.

Within the field of sports-injury genetics, some studies have focused on variations in the genes that control the production of collagen, the main component of tendons and ligaments. Collagen proteins also form the backbone of tissues and bones, but in some people, structural differences in these proteins may leave the body’s structures weaker or unable to repair themselves properly after injury. In a study published in the British Journal of Sports Medicine in 2009, South African researchers found that specific variations of a collagen gene named COL1A1 were under-represented in a group of recreational athletes who had suffered traumatic ACL injuries. Those who had torn their ACL were four times as likely as the uninjured study subjects to have a blood relative who had suffered the same injury, suggesting that genetics are at least partially responsible for the strength of the ligament.

The same COL1A1 gene has also been linked to other soft-tissue injuries, like Achilles-tendon ruptures and shoulder dislocations. In a review article that combined the results of multiple studies on the COL1A1 gene, published in the British Journal of Sports Medicine in 2010, researchers concluded that those with the TT genotype—one of three potential variants of the gene, found only in 5 percent of the population—are extremely unlikely to suffer a traumatic ligament or tendon injury.

However, because of the vast complexity of the human genome, it’s highly improbable that a single variant within a gene can determine a person’s genetic risk for a given soft-tissue injury. Researchers agree it’s much more likely that these injuries, like complex conditions such as obesity or type 2 diabetes, are influenced by multiple genes.  

The COL5A1 gene, another one associated with collagen production, has been linked to a higher risk of injury of the ACL and Achilles tendon, as well as greater susceptibility to exercise-induced muscle cramping. A 2013 study in the Clinical Journal of Sports Medicine found that specific variants of COL5A1 were strongly correlated with muscle cramping among runners in the Two Oceans Marathon in South Africa.

Researchers have also identified genetic markers associated with bone-mineral density, an important measure of bone strength that provides clinicians with information on a patient’s risk of fracture. One gene combination, investigated in a 2010 study in the journal BMC Genetics, was associated with a nearly four-fold increased risk of stress fractures among army recruits. A separate study, published in the Archives of Pediatric Adolescent Medicine in 2009, found that osteoporosis in older women and increased rates of stress fractures in young women also tend to run in a family.

Thus far, though, collegiate and professional sports have made only limited use of genetic testing. After a Rice University football player with sickle-cell anemia died in 2006 from complications related to exercise in the heat, the NCAA began screening players in 2010 to help those with the condition take the proper precautions. And Major League Baseball, after several high-profile instances of identity and age falsification among recruits from the Dominican Republic, began genetic testing in 2009 to verify the age of prospects in Latin America. (Some believe the MLB’s practice may violate the Genetic Information Nondiscrimination Act of 2008, which prevents insurers and employers from considering genetics in their hiring decisions; because the NCAA does not employ its student athletes, it hasn’t faced the same criticism.)

As with other types of genetics research, some are worried that the information discovered by these tests could be used unethically—in this case, that it could lead to discrimination against certain athletes. “Assessing genetic information on injury risk should be dedicated to the benefit of the athlete or individual, not the organization,” Kim says.

But the largest market for sports-injury genetic testing may be the general public. A growing number of companies like 23andMe, Pathway Genomics, DNAFit, and Stanford Sports Genetics offer genetic tests that can tell the average consumer about his or her risk for sports injuries, including ACL ruptures, stress fractures, osteoarthritis, and spinal-disc degeneration.

Knowledge of genetics alone won't keep athletes from getting hurt. But it may, at the very least, reveal those at higher risk and help minimize future problems.  “We are still in the dawning age of genetic testing,” Kim says. “But new research is being conducted on a much greater scale that we hope will help us identify where and how genetic information can be used to avoid injury.”