Letter to the Editor and Response

We welcome the opportunity to respond to the informative letter regarding the terminology of concentric and eccentric. We certainly agree that it is exceedingly important to be as precise and accurate as possible when using these and any scientific terminology. The authors of the letter astutely point out the difference in terminology between movement of a single muscle compared with movement of a limb or body, with which we absolutely agree. However, we believe that we (as well as several other authors) have used the terms concentric and eccentric correctly as defined by the authors of the letter. In our article concerning eccentric strengthening for chronic lateral epicondylosis, the specific single muscle-tendon unit targeted by the eccentric exercise is the extensor carpi radialis brevis (ECRB). Perhaps we are guilty of not being precise enough in pointing out the difference between the eccentric contraction of the ECRB compared with the “extension” motion of the wrist along with the antagonist shortening of the wrist flexor muscle group. Instead, we expected the reader to assume that it should be understood without specifying that the term eccentric refers specifically to the ECRB, rather than the entire wrist or upper extremity. We suspect that many other authors have similarly been imprecise about specifying whether the terms concentric or eccentric refer to specific muscles or entire limb or body motions, even though their implicit meaning was for the terms to apply to single muscles. We agree that nonspecific use of these terms is perhaps more obvious when referring to landing from a jump or run unless a specific muscle is being studied in isolation, and hence, the terms are referring to that specific muscle. There seems to be a slight discordance between the precise theoretical scientific meanings of concentric and eccentric and the more practical clinical meanings. Perhaps, as the letter points out, the practical clinical use of the terms should more carefully specify a particular muscle if that is indeed the intent of the terms.