Fitness, Conditioning May Reduce Leg Injuries - Menstrual Irregularities A Risk Factor In Stress Fractures

Physically active women with lower aerobic fitness and poorer overall fitness may be at greater risk for stress fractures and other lower-extremity overuse injuries. A new study released by the American College of Sports Medicine (ACSM) also found that many women who suffered lower extremity stress fractures had previously experienced a lower extremity non-stress fracture overuse injury. The research was published in the September issue of Medicine & Science in Sports & Exercise®, the official journal of ACSM.


Researchers led by Mitchell J. Rauh, Ph.D., P.T., M.P.H., also noted that menstrual irregularities (six or more consecutive missed menses during the past 12 months) quadrupled the likelihood of a lower-extremity stress fracture during training. "This underscores the importance of bone health for active women," said Rauh. He recommends early screening efforts to identify women with a history of menstrual irregularity, followed by proper medical management.


The study involved 824 female recruits at the Parris Island Marine Corps Recruit Depot in South Carolina. The women, whose average age was 18, completed a questionnaire that included demographic information as well as injury history, physical activity and fitness practices, and menstrual history. Measurements of height and weight allowed researchers to calculate the body mass index (BMI) for each participant. Researchers assessed each recruit's aerobic fitness through a 1.5-mile timed run conducted before the start of training.


During the 13 weeks of Marine Corps basic training, 399 of 824 women (48.4 percent) incurred 868 lower-extremity overuse injuries. Investigators calculated risk of injury per training day exposure (TDE), defined as any day in which the recruit was not held out of training activity because of an injury and was at risk of sustaining a lower-extremity stress fracture or non-stress fracture overuse injury. The 868 injuries over 68,686 TDE yielded a rate of 12.6 per 1,000 TDE. The rate for initial overuse injuries (399 over 46,061 TDE) was 8.7 per 1,000 TDE and the rate for subsequent overuse injuries (469 over 22,625 TDE) was 20.7 per 1,000 TDE. The most common injuries involved the shin, calf, knee, or hip.


"The overall rate of lower extremity subsequent overuse injury was more than double that for initial lower extremity overuse injury," said Rauh. "Further, once injured with a stress fracture, the female recruit was three-and-one-half times more likely to suffer a subsequent stress fracture." Although the study did not specifically examine possible causes for the greater likelihood of reinjury, Rauh said injured recruits:


- May alter their gait to compensate for an injury

- May fatigue more rapidly, predisposing them to subsequent injury

- May have a diminished ability to adapt to new or repeated stressors


After controlling for other potential risk factors, women in the slowest quartile in the timed run (taking more than 14.4 minutes to run 1.5 miles) were 3.3 times more likely to suffer a lower-extremity stress fracture than those in the fastest quartile (12.5 minutes or less). Women who had participated in weight-training activities on a consistent basis for seven or more months were less likely to incur a stress fracture. "Given the high injury rate among recruits who were less fit," said Rauh, "there may be benefit in having recruits participate in aerobic and strength-training programs on a consistent basis at least seven months prior to basic training."


Rauh said overall injury rates in this study were comparable to those noted in previous research. However, the opportunity to measure injuries against training day exposure allowed calculation of risk per TDE. "To our knowledge," he noted, "this is the first study to assess lower-extremity stress fracture and non-stress fracture overuse injury rates using this method of exposure in female recruits."


The American College of Sports Medicine is the largest sports medicine and exercise science organization in the world. More than 20,000 international, national, and regional members are dedicated to advancing and integrating scientific research to provide educational and practical applications of exercise science and sports medicine.


Medicine & Science in Sports & Exercise® is the official journal of the American College of Sports Medicine, and is available from Lippincott Williams & Wilkins.


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