What is Eccentric Strengthening?
Eccentric contraction exercises are an important and often overlooked component of strength training.
By: Dr. Ashley O’Rourke PT, DPT, ATC, LAT
Eccentric strength refers to tension being applied to a muscle as it lengthens. This is also when the muscle’s force-producing capacity is most optimal. Studies show that eccentric exercise results in less oxygen consumption, greater force production, and less energy expenditure than concentric strengthening- or the active shortening of the muscle. The force produced by a concentric contraction is always less than the muscles maximum force. During a voluntary muscle contraction, the speed of the contraction and the ability to exert tension are inversely related. Therefore, the faster a muscle contract concentrically, the lower the tension it is able to generate. An example of concentric strengthening would be a classic bicep curl, whereas the eccentric component would occur as a person lowers the arm into a straightened position (as the bicep muscle lengthens).
Eccentric Strengthening in Post-Op Knee Rehab:
Eccentric quadricep and gastrocnemius (calf) strength, in particular, are important following knee surgeries such as ACL reconstruction because of their importance in absorbing the weight of your body as they lengthen in order to control your descent- this includes going downstairs, sitting down in a chair or decelerating from a sprint. Without sufficient eccentric control, it would be difficult and, in some cases, unsafe to perform these activities. In regards to running, the primary muscles involved in acceleration and deceleration are quadriceps and gastrocnemius. However, acceleration involves the concentric contraction of these muscles, while deceleration involves the eccentric use of these muscles. Therefore, eccentric strength is important to safely slow down following a sprint or before initiating a rapid change of direction. Research suggests that eccentric strengthening on the non-involved lower extremity is also beneficial for improving both the quadriceps muscle strength and the quadriceps accelerated reaction time in the surgical lower extremity.
Concerns with Eccentric Strengthening in Post-Op ACL:
Though the idea of early post-operative eccentric resistance exercise to the surgical limb has traditionally been contraindicated, due to the potential for injury to the graft, articular cartilage, or surrounding soft tissue structure, recent evidence has shown that the application of early eccentrics to the ACL limb can be used to safely increase quadriceps muscle volume and strength. While eccentric quadriceps strength is important to regain following ACL reconstruction, it does not come without caveats. As with any eccentric training program, careful progression of training volume and intensity in the post ACL reconstruction patient is a necessity and should be performed under the direction of a licensed physical therapist as too much eccentric quadriceps strength could increase the chances of anterior tibial translation if not accompanied by sufficient hamstring strength. Therefore, a comprehensive approach, including both concentric and eccentric training to both the anterior and posterior chains surrounding the knee joint should be considered.
Take-Home Message:
Eccentric exercise has the ability to be an effective means to manage many common orthopedic conditions such as tendinopathies, post-op recovery, and muscle strain prevention. This potential is based on muscle/tendon physiology as it relates to performance. Eccentric exercise, or when the muscle is lengthened and an external force exceeds the force produced by the muscle, has been shown to be more effective than traditional concentric strengthening at minimizing muscle atrophy and improving muscle force production. It results in less oxygen consumption, greater force production, and less energy expenditure and should be incorporated into both a preventative strength training program, as well as, an effective post-op rehabilitation protocol.
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