January 04, 2023

Studies suggest there are significant differences in hip and knee alignment and activation in men and women when kicking a soccer ball. Data reveals that males activate certain hip and leg muscles more than females during the motion of the instep and side-foot kicks – the most common soccer kicks – which may help explain why female players are more than twice as likely as males to sustain an Anterior Cruciate Ligament (ACL) injury.

Hips Don't Lie

Prior research shows that females are more prone to non-contact ACL injuries than males, and though many theories exist, a direct cause for the difference is unknown. “By analyzing the detailed motion of a soccer kick in progress, our goal was to home in on some of the differences between the sexes and how they may relate to injury risk,” said orthopedic surgeon Robert Brophy, MD, study author and St. Louis CITY Soccer Club Medical Director. “This study offers more information to help us better understand the differences between male and female athletes, particularly soccer players.” They found that male players activate the hip flexors (inside of the hip) in their kicking leg and the hip abductors (outside of the hip) in their supporting leg more than females.

“Activation of the hip abductors may help protect players against ACL injury,” said Dr. Brophy, Washington University Orthopedics sports medicine division chief. “Since females have less activation of the hip abductors, their hips tend to collapse into adduction during the kick, which can increase the load on the knee joint in the supporting leg, and potentially put it at greater risk for injury.”

Brophy said that although the study does not establish a direct cause-and-effect relationship between muscle activation and knee alignment and ACL injuries, the data “moves us toward better understanding of what may contribute to differences in injury risk between the sexes and what steps we might take to offset this increased risk in females.”

"Focusing on strengthening muscles around the hip may be an important part of programs designed to reduce a female athletes’ risk of ACL injury,” said Dr. Brophy. “Coaches and trainers at all levels, from grade school through professional, should consider using strategies that demonstrate potential to prevent these injuries.”

A Leg to Stand On

Dr. Brophy authored a second study which examined the role of leg dominance in ACL injuries among soccer players. The research suggests that limb dominance does serve as an etiological factor with regard to ACL injuries sustained while playing soccer. For non-contact injuries, roughly half of the injuries occurred in the preferred kicking leg and the contralateral leg. However, by gender, there was a significant difference in the distribution of non-contact injury, as 74.1% of males were injured on the dominant kicking leg compared with 32% of females. 

As the team physician for the former St. Louis Athletica professional women's soccer club and medical director for the newest soccer addition to St. Louis, CITY SC, Dr. Brophy concludes, “EMG and motion analysis demonstrate decreased activation of the hip abductor of the support lower extremity, which may be associated with the higher risk of non-contact ACL injury in this limb for female soccer players compared to male soccer players."

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