Effects of Hamstring Training in Different Modes on Stabilizing Knee Joints With Anterior Drawer Laxity

INTRODUCTION Anterior cruciate ligament (ACL) injuries are commonly seen among athletes, which eventually makes more or less devastating impacts on their performances. Although ACL injuries may result from the knee collision, 70% of them are due to noncontact movements, including abrupt brakes, changing directions at high speed (i.e. sidestep cuttings and crossover cuttings). In doing so, one must at first have his or her axial foot fixed on the ground to absorb the momentum oriented from the original direction. Insufficient eccentric muscles or ligament strength are likely to trigger muscle and ligament injuries.

It is generally agreed that the risk of ligament injuries can be reduced by strengthening a specific muscle group by which the dynamic stability of the joint is able to be enhanced and the static stability provided by the ligament can also be compensated. Traditionally, the strengthening exercise of ACL rehabilitation has been putting an emphasis on the hamstring and quadriceps with an attempt to decrease the anterior drawer instability as well as the shearing force of ACL. Nonetheless, from the aforementioned pathomechanism of ACL injuries, the knee rotators should be valued as they are supposed to . The internal rotators of the knee joint (semitendinosus, semimembranosus and gracilis) are highly related to ACL injuries5. However, the knee rotator strength is often neglected and even sacrificed as an autograft for the ACL reconstruction .

Modifications can be made in progressive resistance exercise for strengthening knee internal rotators. In this current study, 20 subjects with anterior drawer laxity were randomly assigned to three groups adopting different training modes: plate-loaded squat press (SP), plate-loaded kneeling leg curl with internal rotation (KLCIR), and plate-loaded kneeling leg curl (KLC). Static stability, dynamic stability, and isokinetic strength were measured. The purpose of this paper was to find out an optimal solution to the enhancement of the static and dynamic knee stability to a great extent.

MATERIALS AND METHODS Subjects The research program was approved by the Human Subject Committee in Taipei Physical Education College. Knee joint laxity was surveyed by a KT-2000 test (MED Metric Co., San Diego, USA) in the Department of Physical Education and Health at Taipei Physical Education College. The anterior drawer laxity of the knee joint in this study was defined as anterior displacement over 3 mm discrepancy between bilateral knee joints by a KT-2000 test under 20-pound force. According to this criterion, Dale M. et al. demonstrated that 85% (33/39) of this population have complete ACL tears and 15% (6/39) have partial tear. One hundred and seventy-three students were tested and 30 met the criterion, including 22 males and 8 females, although no obvious trauma history was available in some of them. Two males were excluded due to other causes that might affect muscle strength or knee stability such as lower limbs fracture and arthritis. Besides, eight female students were eliminated to avoid possible gender difference. Twenty male students were included in the experimental group. Another 8 male students with stable knees without any medical history of knee injuries were included in the control group. The participants in both experimental and control groups lived a sedentary lifestyle. Stable knees were defined as a discrepancy less than 1.5mm between bilateral knees by a KT-2000 test under 20-pound force.

Flow Path Twenty subjects in the experimental group were randomly assigned into three groups: SP (n=7), KLCIR (n=7) and KLC (n=6). Eight control subjects neither received any training nor was engaged in body-building on their own during the training period. Every subject was asked to fill in basic information, including age, body height, and body weight. Before the experiments, the flow path was explained to each subject who had already signed an informed-consent form.