We conducted a cross-sectional study of female youth soccer players to determine whether lower extremity strength and jump biomechanics differed between elite and recreational players, because researchers have shown these variables are risk factors for injury in other populations. We found a trend for greater hip strength in elite than recreational athletes, but all other measures of hip and knee strength were similar. Athletes were similar in terms of jump biomechanics, years of soccer experience, and history of previous injury.
Hip-abductor strength was not different between groups, which is interesting since hip-abductor strength is thought to play a role in chronic knee injury, such as patellofemoral pain syndrome.34,35
In addition to affecting chronic knee injury, researchers have suggested that hip-abductor strength may affect jump biomechanics,36
and jump biomechanics have been associated with risk for ACL injury.14
Most investigators comparing strength between recreational and elite athletes have focused on quadriceps and hamstrings rather than hip abductors,8,9,12,13
but Thorborg et al32
found greater hip-abductor strength in elite soccer players than in a control group of recreational athletes. They hypothesized that hip abductors were important for kicking, accelerating, and sudden changes of direction, which are necessary skills for soccer.
One notable finding was that strength measurements were similar for all measures of hip strength in this study population (flexion, extension, abduction, adduction). In older participants, hip flexors and extensors are generally stronger than hip abductors and adductors,37
but we could not find any normative data on hip strength in female youth for comparison. Differentiations between muscle groups possibly are not yet prominent in this younger age group.
In contrast to the findings reported by researchers studying adult players,8,9
we did not find any differences in hamstrings or quadriceps strength by soccer level in our youth sample. However, our results are in agreement with those reported in studies of male youth athletes.12,13
In their study of soccer players aged 10 to 14 years, Hansen et al12
found differences between elite and subelite athletes in back and hand-grip strength, but they did not find differences in quadriceps strength after adjusting for age and mass. They did not evaluate hamstrings strength or hip strength. Le Gall et al13
found no differences in hamstrings or quadriceps strength by soccer level in their study of male soccer players aged 14 to 17 years.
We undertook this study to understand more about elite and recreational athletes in the youth population. We had observed that despite the barrier of tryouts and the differing time commitments, girls from elite and recreational teams in the SYSA seemed quite similar, and our data supported this observation. Playing elite soccer in the SYSA requires extensive financial and time commitments from both parents and athletes, and girls who play at this level likely are more motivated to become better soccer players. However, our data did not suggest that they differ in ways that affect their risks of injury. This finding is important because it suggests that clinicians could apply recommendations from research with elite youth athletes to their recreational-athlete patients. The data also suggest that hip-abductor strength might differentiate more-skilled athletes from their less-skilled counterparts, but future studies are needed to determine whether this difference in strength translates into true differences in injury risk.
One of the limitations of our study was the difference in mean age between elite and recreational players. Although the age difference was small (0.7 years), small differences can be correlated with increases in strength due to the proximity to puberty.38,39
We controlled for the age discrepancy using regression analysis; however, residual confounding might exist, and an ideal sample would have been age matched. Another limitation was the potential for measurement error in the strength and jump biomechanics measures. Researchers have reported good reliability using these measures,25,26,27–32
but any measurement error could obscure differences between the groups. We also had a relatively small sample of elite and recreational players, and more subtle differences possibly would be detected with a larger sample size. However, subtle differences in strength or jump biomechanics are unlikely to be relevant to injury risk. Finally, we studied youth soccer players in Seattle, and we cannot speculate about how these athletes compare with youth soccer players in other geographic locations.