By: 1 June 2010



Acute ACL injuries are common knee injuries in sports participants.12,25,29 An ACL injury has a devastating effect on the individual, resulting in high levels of short-term disability and increasing the likelihood of secondary knee disorders, such as osteoarthritis, in later life.19,26,29,30,32 In sports, women have an ACL injury rate 3 to 10 times higher than the rate in men.2,8,20,22 The primary mechanism of the injury is non-contact in nature; that is, there is no physical contact between the patient and other people at the time of injury.4,24,26 The non-contact nature of the majority of ACL injuries suggests that the intrinsic forces generated by patients themselves are likely to be an important cause.10,15,16,30 Previous studies have shown that non-contact ACL injuries mainly occur in the performance of certain athletic tasks, such as stop-jump, landing, and cutting.1,2,4,11,14

Previous studies have also shown that female recreational athletes have lower extremity motor controls that may increase the load on their ACLs in specific athletic tasks, in comparison with their male counterparts.7,21 For our long-term studies on the prevention of non-contact ACL injuries, we therefore hypothesised that women tend to have altered lower extremity motor controls that, in specific athletic tasks, frequently bring them close to positions in which non-contact ACL injuries may occur, thereby increasing their risk for non-contact ACL injuries.

One of the characteristics of female recreational athletes’ movement is their small knee flexion angle in landing tasks that are preceded with horizontal movements, such as stop-jump tasks.7,21 Regarding biomechanics, decreasing the knee flexion angle at landing increases the loading on the ACL5,13,23,28,31 and thereby increases the risk for ACL injuries. As a natural continuation of our preliminary studies, the purpose of this study was to address the effects of constraining knee extension on lower extremity kinematics and kinetics by having recreational athletes wear a specially designed knee brace during a stop-jump task. It was hypothesized for this study that the specially designed knee brace would significantly increase the knee flexion angle at the landing of the stop-jump task and that the maximum ground reaction forces would be reduced as the knee flexion angle at landing increased.

Materials and Methods


Twelve male and 12 female healthy recreational athletes between 18 and 28 years of age without known histories of knee disorders were recruited as the subjects for this study (Table 1). A recreational athlete was defined as a person who plays sports 2 to 3 times per week regularly without following a professionally designed training scheme. All subjects were recruited through advertising from the general student population on a university campus. The use of human subjects was approved by the institution’s internal review board.

Table 1

Subject Mean Age, Height, and Weight

Gender Age, Y Body Weight, kg Standing Hegiht, m
Male 26.0