Lengthening of the pectoralis minor muscle during passive shoulder motions and stretching techniques: a cadaveric biomechanical study.

Background and Purpose. Lengthening of the pectoralis minor muscle (PMi) during passive shoulder motions and the effect of stretching techniques for this muscle are unclear. The purposes of this study were: (1) to investigate the amount and pattern of the lengthening between passive shoulder motions and (2) to determine which stretching technique effected the greatest change ill PMi length. Methods. Nine fresh cadaveric transthoracic specimens were used. Lengthening in the lateral and medial fiber group of the PMi was directly measured during 3 passive shoulder motions (flexion, scaption, and external rotation at 90 degrees of abduction) and 3 stretching techniques (scapular retraction at 0 degrees and 30 degrees of flexion and horizontal abduction) for this muscle. The measurement was conducted by using a precise displacement sensor. Results. Although the length of the PMi linearly increased during all shoulder motions, lengthening during flexion and scaption was steeper and significantly larger than that during external rotation at 90 degrees of abduction. For the stretching techniques, scapular retraction at 30 degrees of flexion and horizontal abduction stretched the PMi more than scapular retraction at 0 degrees of flexion. In comparison with lengthening at 150 degrees of flexion, scapular retraction at 30 degrees of flexion significantly stretched the medial fiber group of the muscle. Discussion and Conclusion. The extensive lengthening of the PMi is necessary during shoulder motions, especially flexion and scaption. Scapular retraction at 30 degrees of flexion makes the greatest change in PMi length. This Study suggests the importance of the PMi ill Shoulder motion and provides anatomical and biomechanical evidence that might guide appropriate selection of stretching techniques.