Sunday, August 9, 2009

Injury Risks for the Female Athlete - Part 1 (the most running-related post yet!)

I've been working on an article for the ACSM Health & Fitness Journal about injury risk to the female athlete. The first submission got sent back with a bunch of comments, so I figured as I'm revising I'll post it in a few installments. To the runners/active women out there, it'll hopefully be of some use.

Injury Risks for the Female Athlete

While there are more and more studies showing differences between men and women’s physiology and specifically their response to exercise, historically nearly all studies have been done on men. Thus, most of the data available to the public (in scientific journals, textbooks, and encyclopedias), while providing a great deal of insight into the physiology of exercise, disregards large portions of the population and is severely limited in scope. Because of women’s unique set of physiological responses and health concerns, it is important to consider women as a specific sub-population in the study of exercise and athletics. This article will focus on the topic of injury risk for women, reviewing the current literature on this subject to better understand the special concerns of the female athlete.

The increasing number of women participating in sports also means that more women are likely to sustain injury. While the timing, location, and nature of an injury may vary from person to person, there are specific injury risks for the female athlete. In particular, women are more likely than men to sustain musculoskeletal injuries during physical activity [10], as well as lower-extremity injuries in general [21]. By far the most documented injury in female athletes is the anterior cruciate ligament (ACL) tear. Studies have reported the occurrence of ACL tears in women as up to nine times greater than in men [15]. In soccer and basketball in particular, women are three times more likely to tear their ACL than males [15]. Suggested reasons for greater injury incidence in women have ranged from biomechanics to coordination and fatigue to ligament and tendon properties. To further understand the sex differences associated with injuries and take steps to prevent them, it is crucial to examine these risk factors.

Biomechanical differences are perhaps the most noticeable factor that can predispose a woman to injury. Gait studies have identified particular differences in the up and down motion of the pelvis (or pelvic obliquity) and vertical motion of the whole body. Women generally have greater pelvic obliquity, which translates into less vertical motion [20]. This is a more biomechanically efficient gait, because less energy is expended lifting the body up and down with each stride. However, the greater pelvic motion also causes movement of the lower spine, which has been associated with acute and chronic back pain as well as disc damage. Thus there may be tradeoff between gait efficiency and injury risk – what serves as an advantage for women in conserving energy may promote the development of low back pain.

Studies on the biomechanics of landing from a jump have demonstrated several differences in men and women. Women land with their knees less flexed and turned slightly more inwards than men [14]. The inward turning of the knee is called knee valgus. Both knee flexion and valgus angle have been associated with knee injury and ligament damage. While landing with knees less flexed (and legs more extended) helps decelerate the body from a fall and can absorb more impact from the landing, it puts much more strain on the ACL. Even slight increases in valgus angle (as little as 2 degrees) can increase the force on the ACL by threefold and potentially cause injury. Women have an average of 4.5 degrees greater knee valgus than men during jump landings [14]. This biomechanical difference has important implications for females participating in sports that require jump landings, such as volleyball, basketball, and track and field. Awareness of women’s higher susceptibility to ligament injury may encourage injury prevention and emphasis on correct landing techniques.

Another explanation for increased injury risk in women is neuromuscular fatigue. There is a significant link between fatigue and injury, for example game-related injuries occur much more often at the beginning or end of a season [9]. Injury may occur due to vigorous pre-season training or the accumulated strain of many competitions at the peak of the season. Other studies have reported a higher incidence of knee injuries during the last 15-30 minutes of soccer or rugby matches, which corresponds to the time at which athletes are physically exhausted from the game. Neuromuscular control of the legs is important during maneuvers like landing from a jump or moving from side-to-side, and lack of control is likely to cause injury [9]. High intensity sports that incorporate quick movements and place a high load on the joints (like basketball, soccer, and football) require sustained effort that can fatigue an athlete. The accumulation of fatigue lowers the force-generating capacity of the muscle, affects motor control, and slows reaction times [6]. These deficiencies may change how an athlete performs landing and side-to-side movements, which may lead to injury. Several studies have indicated that women show a greater performance change with fatigue than men, such as a reduced capacity to control the knee and hip joints [6]. These abnormal movements may increase female athlete’s risk for injury, especially of the ACL.

6. Kernozek TW, Torry MR, Iwasaki M. Gender Differences in Lower Extremity Landing Mechanics Caused by Neuromuscular Fatigue. Am J Sports Med. 2008;36(3):554-65.

9. McLean SG, Felin RE, Suedekum N, Calabrese G, Passerallo A, Joy S. Impact of fatigue on gender-based high-risk landing strategies. Med Sci Sports Exerc. 2007;39(3):502-14.

10. Miller BF, Hansen M, Olesen JL, Schwarz P, Babraj JA, Smith K, Rennie MJ, Kjaer M. Tendon collagen synthesis at rest and after exercise in women. J Appl Physiol. 2007; 102(2):541-6.

14. Pappas E, Hagins M, Sheikhzadeh A, Nordin M, Rose D. Biomechanical differences between unilateral and bilateral landings from a jump: gender differences. Clin J Sport Med. 2007;17(4):263-8.

15. Prodromos CC, Han Y, Rogowski J, Joyce B, Shi K. A meta-analysis of the incidence of anterior cruciate ligament tears as a function of gender, sport, and a knee injury-reduction regimen. Arthroscopy. 2007;23(12):1320-1325.

20. Smith LK, Lelas JL, Kerrigan DC. Gender differences in pelvic motions and center of mass displacement during walking: stereotypes quantified. J Womens Health Gend Based Med. 2002;11(5):453-8.21.

21. van Gent RN, Siem D, van Middelkoop M, van Os AG, Bierma-Zeinstra SM, Koes BW. Incidence and determinants of lower extremity running injuries in long distance runners: a systematic review. Br J Sports Med. 2007;41(8):469-80.

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