Eccentric contractions require unique activation strategies by the nervous system.
Eccentric contractions occur when activated muscles are forcibly lengthened. This mode of muscle function occurs frequently in the activities of daily living and in athletic competition. This review examines the experimental evidence that provides the foundation for our current understanding of the benefits, consequences, and control of eccentric contractions. Over the past several decades, numerous studies have established that eccentric contractions can maximize the force exerted and the work performed by muscle; that they are associated with a greater mechanical efficiency; that they can attenuate the mechanical effects of impact forces; and that they enhance the tissue damage associated with exercise. More recent evidence adds a new feature to this repertoire by suggesting a new hypothesis: that the neural commands controlling eccentric contractions are unique. Examination of this hypothesis is critical because the existence of such a control scheme would increase substantially the complexity of the strategies that the nervous system must use to control movement.