This article originally appeared in the German web site medicalsportsnetwork.de in August, 2011.
Scientiﬁc evidence for core stability in sport injury prevention
By Ajit M.W. Chaudhari, PhD
Anecdotal data throughout the scientific literature and popular press advocate for improved core stability for injury treatment and preventionof conditions involving the lower extremity as well as low back and upper extremity. However, these interventions are generally assembled using the conservative approach of including every exercise that might provide some benefit. Rigorous scientific studies have not yet been performed to establish evidence-based criteria for the inclusion or exclusion of core stability exercises.
What is “Core”?
The “core” is a vague term that nevertheless has been widely used to describe some portion of the body extending approximately from mid-thigh to mid-chest, including the joints of the lower thoracic and lumbar spine and the hip joints as well as the muscles that induce movements about these joints. Some researchers have focused on the muscles crossing the hip because of their role in pelvic stabilization. These muscles also act as prime movers of the lower extremity. Other researchers have focused on the trunk muscles, those that cross the lumbar spine to generate movement of the upper torso, because of their role in the etiology of low back pain. These muscles may also influence the forces acting on the lower extremity by stabilizing the torso over the pelvis.
What is “Stability”?
“Stability” can be defined as the ability of a system to return to its original position or state in response to an internal or external perturbation. A stable athlete can hold his/her position or continue on the same path towards a goal even when bumped by an opposing player, while an unstable athlete may be thrown off course or knocked into a position where injury can occur. It is extremely important when considering the role of stability that it is not the same as stiffness or strength. Just as a tightrope walker needs to make rapid adjustments to maintain her position on the tightrope, the ability to make these rapid adjustments is as important as being strong for an athlete to maintain stability.
How could core stability prevent sport injury?
Most musculoskeletal sport injuries occur due to excessive forces being applied to at-risk structures. These excessive forces can occur acutely to cause frank rupture, such as in an anterior cruciate ligament (ACL) injury, or they can occur chronically at a level that is just high enough to cause micro-damage that accumulates over time, such as in a tibial stress fracture. For the lower extremity in particular, much of the force experienced is a consequence of the relatively large mass and momentum of the torso. A lack of core stability could therefore potentially lead to situations where the torso leans outside the base of support, increasing forces on the lower extremity. In throwing motions, energy is generated first in the legs, then transmitted across the core to the throwing arm. In this case, a lack of core stability might prevent this energy transmission, potentially leading the thrower to compensate by excessively using his shoulder muscles to generate the desired velocity of the ball. While these theories have not been rigorously proven, they have served as the impetus for the panoply of proposed exercises and equipment to build the strength of the core muscles.
What evidence exists for core stability in sport injury prevention?
Very few rigorous scientific studies have established the role of improved core stability in sport injury prevention. Two recent studies performed at Yale University on intercollegiate athletes investigated deficits in trunk proprioception and trunk neuromuscular control following sudden perturbations, and found that each of these deficits were associated with two to three times greater likelihood of developing a subsequent knee injury across all sports. Other research studies performed in the United States, Canada, Germany and Norway have identified several successful ACL injury prevention programs that include core stability exercises, but it remains unknown whether the core stability component of these programs provides any benefit. In a recently completed study by our group at The Ohio State University, commonly prescribed trunk stabilization exercises including prone and side plank, supine bridge, lunge, and abdominal curl exercises had no effect on core stability or lower extremity joint forces, although they did improve core strength and endurance. These exercises were not as dynamic nor did they include external perturbations to the athlete like the successful ACL injury prevention programs do, which suggests that dynamic movement and perturbation may be necessary elements to improve core stability.
In spite of the wide array of exercise regimens proposed and equipment available for improving core stability in the scientific literature, popular press, and marketplace, the evidence does not exist to make a recommendation to include or exclude core stability exercises in sport injury prevention. Future rigorous evaluation of the efficacy of these existing programs and equipment, including tracking injury rates, will be necessary to determine whether improving core stability provides protection against sport injury.