F-12K Free Communication/Poster Athletic Performance
Female athletes have a 4 times greater incidence of injury to the Anterior Cruciate Ligament (ACL) than males. Research has shown plyometric training can decrease landing forces and increase activity of the hamstring muscles when jumping and landing. Closed kinetic chain strength exercises for the lower extremities recruit both the quadriceps and hamstrings to stabilize the knee joint. When the foot is in contact with the ground, the hamstring muscles act to reduce stress on the ACL. Thus, a strong contraction of the hamstrings and a decrease in landing forces could diminish the likelihood of ACL injuries.
The purpose of this study was to determine the effect of open kinetic chain (OKC) and closed kinetic chain (CKC) strength training on landing forces and corresponding electromyographical (EMG) activity of the quadriceps and hamstrings during a stabilization drop.
Thirty female college volleyball players participated in a 6-week periodized training program consisting of either OKC or CKC exercises. Pre- and post-training, the subjects performed a drop stabilization from a 20-inch box onto a forceplate measuring ground reaction forces (GRF) and corresponding times at 200 Hz. Prior to testing, subjects were fitted with surface EMG electrodes on the Rectus Femoris (RF), Vastus Lateralis Oblique (VLO), Biceps Femoris (BF), and Gastrocnemius (GA). EMG data were filtered, rectified and integrated. Paired t-tests were used to compare dependent variables pre- and post-training and alpha was set at p <.05.
All GRF's remained unchanged in both groups. The time of foot contact to time of Fzpeak was unchanged. Integrated EMG signals increased in RF (.4 + .1v), VLO (.4+.1v), BF (.2+.1), and GA (.8+.3v) for the OKC and in the RF (.3+.1v), VLO (.6+.1v), and GA (.5+.2v) for the CKC.
Six weeks of strength training alone may not reduce landing forces or change neuromuscular patterns to protect the ACL in female athletes.