Comparison of the Angular Compartment of Hip Flexion Before and After Training in 11 to 12-Year-old Soccer Players

An anterior cruciate ligament (ACL) injury is an important cause of rest in athletes. In most cases, ACL injuries do not require external contact and they are associated with biomechanical risk factors that increase ACL tension. The increase of the hip flexion angle (HF) is included within these. The ACL requires cooperation of the periarticular musculature of the knee, muscle groups, hip stabilizers and CORE muscles; consequently, fatigue caused by exercise would alter the balance and put this ligament at risk.


Introduction
The anterior cruciate ligament injury (ACL) is an important cause of lost days for athletes and it is the most common reason for injuries that require more than eight weeks of recovery 1 . This injury usually occur while practicing sports and it is more common during competition than during training 2 . The predominant mechanism is a pivot shift type injury, which occurs without contact in the support leg. This mechanism is a combination of hip and knee flexion associated with internal rotation and initial valgus of the knee and, finally, an external rotation of the tibia 1,3,4 .
Biomechanical risk factors have been proposed for ACL tear such as an increase in knee valgus moment, increased hip flexion and lesser knee flexion, also greater ground reaction force during the fall would increase ACL tension, bringing it closer to its moment of failure 5,6,7,8,9,10,11 .
Bowerman et al demonstrated that fatigue is related to a decrease in motor balance, which in turn causes a decrease in neuromuscular response, thus increasing the risk of injury to the stabilizing structures 12 . A study examined non-athletic and healthy adult subjects before and after a workout, and they observed that both in men and women, fatigue produced an increase in the anterior translation of the tibia 13 . However, these findings have not been systematically reproduced. Increased tibial translation after conducting strenuous training only on the left knee are also a finding in Skinner studies 14 , but this not happen when isokinetic exercises were execcuted 15 .
On the other hand, epidemiological studies have shown that the majority of ACL injuries occur during the last 15 minutes of the first half and the last 30 minutes of the second half of a game, so, once again, fatigue could be an important risk factor.
These contradictions in the findings can be explained by the type of training applied to the subjects under study and by the manner in which the deficit produced by fatigue was measured 16 Nevertheless,there are no studies in the literature of the effects of everyday training on the biomechanics of hip flexion. This must be the initial approach for measuring the risk of suffering lower extremity injuries for each athlete. The objective of this work is to analyze the effect of soccer training on the biomechanics of hip flexion and to relate these findings to the risk of ACL tear.

Our
Ethics Committee approved our

Results
Fifty male individuals were included. The demographic data of the participants is summarized in  (Figures 1 to 3).

Discussion
In the present study, 11 to 12 year old male subjects belonging to four children's soccer schools in the city of Santiago were evaluated. Within the strengths of the research, we identified the use of inertial sensors, which are highly reliable for measuring the biomechanical variables under study 19,20 .
Standardized training is similar to the training that the subjects perform week by week; therefore, its use is valid for establishing the degree of fatigue that they reach and identifying the risk that they are exposed to.
In addition, they wore the usual clothing (shoes) and   for which the psychological state and stress were favored with the control of these variables.

Conclusion
Sports training in our study group showed that hip flexion is modified by the fatigue achieved after normal training. Hip flexion could be the biomechanical factor that is first altered by fatigue, which should be handled by the technical team in order to prevent ligament injuries.

Funding
This study was supported by the Universidad Metropolitana de Ciencias de la Educación (UMCE).