In response to the letter to the editor regarding: Resting pectoralis minor muscle length: An accurate way to determine if the muscle is shortened?

We appreciate the comments and constructive criticism of our recently published manuscript in Journal of Hand Therapy by Ebaugh, Finley and Goodstadt. The authors offer a valuable and thought-provoking perspective on muscle length and extensibility and how those properties affect movement. We think it is important to first define extensibility and shortening as these are different yet related properties of the muscle. Extensibility is described as the muscles' ability to extend or lengthen, whereas shortening is a decrease in muscle resting length. The amount of extensibility depends on the ability of both active and passive structures to lengthen, is related to tissue stiffness, and may also be influenced by an individual's tolerance to end-range stretch discomfort. Muscle resting length results from a combination of anatomy, posture, and habitual use and likely reflects some adaptations in active and passive tissue structures that may also affect the amount of excursion possible. Based on these descriptions of excursion and length, we believe that different instruments and/or methods are needed to measure each property. Although Finley et al have suggested a method to measure extensibility of the pectoralis minor (PM), we propose that this measurement may simply be measuring PM length change rather than extensibility. Measuring extensibility should include reaching the end range of a muscles' length through positioning and some quantification of resistance to lengthening. For PM, the positioning required to reach end range of the muscle is some combination of scapula upward rotation, elevation, retraction, and posterior tilting, but the individual quantities and sequence of this combination is unknown. In addition, the influence of other muscles' extensibility on positioning for PM may also limit the ability to reach end range. We attempted to simplify this problem by using only scapula retraction as an estimate of end range but admit that the validity of this positioning is lacking.