Zazulak BT, Hewett TE, Reeves NP, Goldberg B, Cholewicki J. Deficits in Neuromuscular Control of the Trunk Predict Knee Injury Risk: A prospective Biomechanical-Epidemiologic Study. American Journal of Sports Medicine, 2007, 35: 1123-1130.
The purpose of this study was to “identify potential neuromuscular factors related to core stability” that could influence lower extremity motion and injury. They defined core stability as the ability to maintain or resume an equilibrium position of the trunk after perturbation.” Although the apparatus that restrained the lower extremity in a fixed position was far from functional, one of the very positive features of this study was the prospective approach where athletes were studied over a three-year period.
A total of 227 athletes were tested and then monitored for knee injuries. There were 140 female and 137 male volunteers. The subjects were positioned upright in the apparatus that constrained the lower extremity from the pelvis to the foot. The trunk was free to move. A force was applied to the trunk in three different directions that would pull the trunk into flexion, extension, or lateral flexion. Once the subjects were able to resist the external force, the force was released at a time that was not known to the subjects. Upon release of the force, the trunk would deviate from its original position and then return. The magnitude of the trunk reaction at 150 milliseconds, and the maximum deviation from initial position were measured. After following the subjects over the three-year period, they compared the trunk control data to the injury history to determine if trunk control measured in this study was related to risk of knee injury (general knee injury, ligament injury, ACL injury).
Over the three-year period, 25 athletes sustained a knee injury (11 female and 14 male). Eleven were ligament injuries (5 female) and six were ACL tears (4 female). Some of the important findings were that when data from the male and female subjects was combined, trunk displacement at 150 milliseconds and maximum trunk displacement were significantly different for the injured and non-injured subjects. When the female subjects were analyzed, the 11 that had ligament injuries had statistically greater maximum displacement compared with the non-injured. This was not true of the male subjects. Lateral displacement may be more important than other directions, but some of the data was not reported in the article. A logistic regression model was created that determined sensitivity and specificity of prediction.
Why is this study important to movement practitioners? Although the methodology for the measurements was “far” from functional, it does document the link between the trunk and the knee with regard to injury. This result is not surprising to practitioners of Applied Functional Science®. They would expect this result because the Principle of Chain Reaction® recognizes that the body is an integrated system. The relationship between the trunk and the knee is true not only for injuries, but for all function. Training the trunk will not only reduce injuries, but it will also enhance function. Dr. Gary Gray, for more than 30 years of Chain Reaction® seminars, has guided participants through a biomechanical movement assessment that clearly shows that the abdominal muscles are an essential “protector” of the ACL. Training the trunk, or the core, or the abdominals would not be performed lying supine asking the client to do sit-ups. Rather the training movements would be done upright, with the arms, legs, and pelvis creating movements that would displace the trunk and require the system to decelerate the movement and return under stable control. The focus is on motion (mobility) and control of that motion (stability) or what we call at Gray Institute® “Mostability.”